diff --git a/bin/doctest b/bin/doctest
index 4e1a7ba..59e0475 100755
--- a/bin/doctest
+++ b/bin/doctest
@@ -13,6 +13,7 @@ require ('child_process')
   process.execPath,
   ['--experimental-import-meta-resolve',
    '--experimental-vm-modules',
+   '--no-warnings',
    ...(flags ? args[idx + 1].split (/\s+/) : []),
    '--',
    path.resolve (__dirname, '..', 'lib', 'command.js'),
diff --git a/lib/Effect.js b/lib/Effect.js
index 86c8fa9..616c96d 100644
--- a/lib/Effect.js
+++ b/lib/Effect.js
@@ -1,27 +1,30 @@
+import {Result} from './Output.js';
+
+
 //    Failure :: Any -> Effect
 const Failure = exception => ({
   tag: 'Failure',
   exception,
 });
 
-//    Success :: Any -> Effect
-const Success = value => ({
+//    Success :: Output -> Effect
+const Success = output => ({
   tag: 'Success',
-  value,
+  output,
 });
 
-//    effect :: (Any -> a) -> (Any -> a) -> Effect -> a
+//    effect :: (Any -> a) -> (Output -> a) -> Effect -> a
 const effect = failure => success => effect => {
   switch (effect.tag) {
     case 'Failure': return failure (effect.exception);
-    case 'Success': return success (effect.value);
+    case 'Success': return success (effect.output);
   }
 };
 
 //    encase :: AnyFunction -> ...Any -> Effect
 const encase = f => (...args) => {
   try {
-    return Success (f (...args));
+    return Success (Result (f (...args)));
   } catch (exception) {
     return Failure (exception);
   }
diff --git a/lib/Output.js b/lib/Output.js
new file mode 100644
index 0000000..1b91c2a
--- /dev/null
+++ b/lib/Output.js
@@ -0,0 +1,8 @@
+//    Channel :: String -> Any -> Output
+const Channel = channel => value => ({channel, value});
+
+//    Result :: Any -> Output
+const Result = Channel (null);
+
+
+export {Channel, Result};
diff --git a/lib/command.js b/lib/command.js
index 608525b..29d47ee 100644
--- a/lib/command.js
+++ b/lib/command.js
@@ -6,10 +6,25 @@ import doctest from './doctest.js';
 import program from './program.js';
 
 
+const bold   = text => '\u001B[1m'  + text + '\u001B[22m';
+const invert = text => '\u001B[7m'  + text + '\u001B[0m';
+const blue   = text => '\u001B[34m' + text + '\u001B[0m';
+const purple = text => '\u001B[35m' + text + '\u001B[0m';
+
+//    formatLine :: (String -> String) -> Array Line -> String
+const formatLine = colour => line => `${
+  invert (` ${`${line.number}`.padStart (4)} `)
+} ${
+  colour (line.text)
+}`;
+
 //    formatEffect :: Effect -> String
 const formatEffect = (
-  effect (x => `! ${x}`)
-         (show)
+  effect (e => `${bold ('throw')} ${show (e)}`)
+         (output =>
+            output.channel == null
+            ? show (output.value)
+            : `${bold (output.channel)} (${show (output.value)})`)
 );
 
 (async () => {
@@ -27,25 +42,27 @@ const formatEffect = (
       process.exit (0);
     }
 
-    const messages = output.map (test =>
+    const failures = output.flatMap (test =>
       comparison (actual => expected => [
-                    `FAIL: expected ${
-                      formatEffect (expected)
-                    } on line ${
-                      test.lines.output[0].number
-                    } (got ${
-                      formatEffect (actual)
-                    })\n`,
+                    [[''],
+                     test.lines.input.map (formatLine (blue)),
+                     test.lines.output.map (formatLine (purple)),
+                     [''],
+                     actual.map (a => blue (formatEffect (a))),
+                     expected.map (e => purple (formatEffect (e))),
+                     ['']]
+                    .flat ()
+                    .join ('\n'),
                   ])
                  (_ => [])
                  (test.comparison)
     );
-    const failures = messages.flat ();
 
     if (!program.silent) {
-      process.stdout.write (`running doctests in ${path}...
-${(messages.map (m => m.length === 0 ? '.' : 'x')).join ('')}
-${failures.join ('')}`);
+      process.stdout.write (`
+Running doctests in ${bold (path)}...
+${failures.join ('')}
+`);
     }
 
     process.exit (failures.length > 0 ? 1 : 0);
diff --git a/lib/doctest.js b/lib/doctest.js
index 6431c7b..26ae981 100644
--- a/lib/doctest.js
+++ b/lib/doctest.js
@@ -19,91 +19,125 @@ import show from 'sanctuary-show';
 import Z from 'sanctuary-type-classes';
 
 import {Incorrect, Correct} from './Comparison.js';
-import {Failure, Success, effect, encase} from './Effect.js';
+import {Success, effect, encase} from './Effect.js';
 import {Line} from './Line.js';
+import {Channel} from './Output.js';
 import require from './require.js';
 
 
-//    indentN :: Integer -> String -> String
-const indentN = n => s => s.replace (/^(?!$)/gm, ' '.repeat (n));
-
-//    formatLines :: Integer -> NonEmpty (Array Line) -> String
-const formatLines = indent => lines => (
-  lines
-  .map (line => `{number: ${show (line.number)}, text: ${show (line.text)}},`)
-  .join ('\n' + ' '.repeat (indent))
-);
-
-//    formatInput :: Integer -> NonEmpty (Array Line) -> String
-const formatInput = indent => lines => (
-  lines
-  .map (line => line.text.replace (/^\s*([>]|[.]+)[ ]?/, ''))
-  .join ('\n' + ' '.repeat (indent))
-);
-
-//    formatOutput :: Integer -> NonEmpty (Array Line) -> String
-const formatOutput = indent => lines => {
-  const [head, ...tail] = lines.map (line => line.text.replace (/^\s*/, ''));
-  const match = /^![ ]?([^:]*)(?::[ ]?(.*))?$/.exec (head);
-  return [
-    `${head.startsWith ('!') ? 'throw' : 'return'} (`,
-    `  ${match == null ? head : `new ${match[1]}(${show (match[2] ?? '')})`}`,
-    ...(tail.map (text => '  ' + text.replace (/^[.]+[ ]?/, ''))),
-    ')',
-  ].join ('\n' + ' '.repeat (indent));
-};
+const wrapJs = sourceType => logFunctions => ({input, outputs}) => {
+  let source = '';
+  for (const {text} of input.lines) {
+    source += text.replace (/^\s*([>]|[.]+)[ ]?/, '') + '\n';
+  }
 
-const wrapJs = sourceType => test => {
-  const source = formatInput (0) (test.input.lines);
-  const ast = acorn.parse (
-    source.startsWith ('{') && source.endsWith ('}') ? `(${source})` : source,
-    {ecmaVersion: 2023, sourceType}
-  );
-  const {type} = ast.body[0];
-  if (type !== 'ExpressionStatement') return source;
+  if (
+    acorn.parse (
+      source.replace (/^[{].*[}]\n$/s, '($&)'),
+      {ecmaVersion: 2023, sourceType}
+    )
+    .body[0].type !== 'ExpressionStatement'
+  ) return source;
 
-  return `
-__doctest.enqueue({
-  input: {
-    lines: [
-      ${formatLines (6) (test.input.lines)}
-    ],
-    thunk: () => {
-      return (
-        ${formatInput (8) (test.input.lines)}
+  source = '';
+  source     += '\n';
+  source     += '__doctest.enqueue({\n';
+  source     += '  input: {\n';
+  source     += '    lines: [\n';
+  for (const {number, text} of input.lines) {
+    source   += `      {number: ${show (number)}, text: ${show (text)}},\n`;
+  }
+  source     += '    ],\n';
+  source     += `    thunk: ([${logFunctions.join (', ')}]) => {\n`;
+  source     += '      return (\n';
+  for (const {text} of input.lines) {
+    source   += `        ${text.replace (/^\s*([>]|[.]+)[ ]?/, '')}\n`;
+  }
+  source     += '      );\n';
+  source     += '    },\n';
+  source     += '  },\n';
+  source     += '  outputs: [\n';
+  for (const {lines, channel} of outputs) {
+    source   += '    {\n';
+    source   += '      lines: [\n';
+    for (const {number, text} of lines) {
+      source += `        {number: ${show (number)}, text: ${show (text)}},\n`;
+    }
+    source   += '      ],\n';
+    source   += `      channel: ${show (channel)},\n`;
+    source   += `      thunk: ([${logFunctions.join (', ')}]) => {\n`;
+    {
+      const parts = lines.map (line =>
+        line.text.replace (/^\s*([.]+[ ]?)?/, '')
       );
-    },
-  },
-  output: ${test.output && `{
-    lines: [
-      ${formatLines (6) (test.output.lines)}
-    ],
-    thunk: () => {
-      ${formatOutput (6) (test.output.lines)};
-    },
-  }`},
-});
-`;
+      const options = {
+        ecmaVersion: 2023,
+        allowReturnOutsideFunction: true,
+      };
+      let isExpression = false;
+      try {
+        isExpression = (
+          (acorn.parse (parts.join ('\n'), options)).body[0].type
+          !== 'ExpressionStatement'
+        );
+      } catch {}
+      if (isExpression) {
+        for (const part of parts) {
+          source += `        ${part}\n`;
+        }
+      } else {
+        source   += '        return (\n';
+        for (const part of parts) {
+          source += `          ${part}\n`;
+        }
+        source   += '        );\n';
+      }
+    }
+    source   += '      },\n';
+    source   += '    },\n';
+  }
+  source     += '  ],\n';
+  source     += '});\n';
+  return source;
 };
 
-const wrapCoffee = test => `
-__doctest.enqueue {
-  input: {
-    lines: [
-      ${formatLines (6) (test.input.lines)}
-    ]
-    thunk: ->
-      ${formatInput (6) (test.input.lines)}
+const wrapCoffee = logFunctions => ({input, outputs, indent}) => {
+  let source = '';
+  source     += `${indent}__doctest.enqueue {\n`;
+  source     += `${indent}  input: {\n`;
+  source     += `${indent}    lines: [\n`;
+  for (let {number, text} of input.lines) {
+    number = show (number);
+    text = show (text);
+    source   += `${indent}      {number: ${number}, text: ${text}}\n`;
+  }
+  source     += `${indent}    ]\n`;
+  source     += `${indent}    thunk: ([${logFunctions.join (', ')}]) ->\n`;
+  for (const {text} of input.lines) {
+    source   += `${indent}      ${text.replace (/^\s*([>]|[.]+)[ ]?/, '')}\n`;
   }
-  output: ${test.output && `{
-    lines: [
-      ${formatLines (6) (test.output.lines)}
-    ]
-    thunk: ->
-      ${formatOutput (6) (test.output.lines)}
-  }`}
-}
-`;
+  source     += `${indent}  }\n`;
+  source     += `${indent}  outputs: [\n`;
+  for (const {lines, channel} of outputs) {
+    source   += `${indent}    {\n`;
+    source   += `${indent}      lines: [\n`;
+    for (let {number, text} of lines) {
+      number = show (number);
+      text = show (text);
+      source += `${indent}        {number: ${number}, text: ${text}}\n`;
+    }
+    source   += `${indent}      ]\n`;
+    source   += `${indent}      channel: ${show (channel)}\n`;
+    source   += `${indent}      thunk: ([${logFunctions.join (', ')}]) ->\n`;
+    for (const {text} of lines) {
+      source += `${indent}        ${text.replace (/^\s*([.]+[ ]?)?/, '')}\n`;
+    }
+    source   += `${indent}    }\n`;
+  }
+  source     += `${indent}  ]\n`;
+  source     += `${indent}}\n`;
+  return source;
+};
 
 //    contiguous :: Line -> NonEmpty (Array Line) -> Boolean
 const contiguous = line => lines => (
@@ -114,6 +148,7 @@ const rewriteJs = sourceType => ({
   prefix,
   openingDelimiter,
   closingDelimiter,
+  logFunctions,
 }) => input => {
   const comments = [];
   acorn.parse (input, {
@@ -166,7 +201,7 @@ const rewriteJs = sourceType => ({
         .lines
   )
   .reduce (
-    (accum, {value, start, end, number}) => {
+    (accum, {value, start, number}) => {
       if (value.startsWith (prefix)) {
         const text = value
                      .slice (prefix.length)
@@ -177,16 +212,29 @@ const rewriteJs = sourceType => ({
         } else if (text === closingDelimiter) {
           accum.state = 'closed';
         } else if (text.startsWith ('>')) {
-          accum.tests.push ({[accum.state = 'input']: {lines: [line], start}});
+          accum.state = 'input';
+          accum.tests.push ({
+            input: {channel: null, lines: [line], start},
+            outputs: [],
+          });
         } else if (text.startsWith ('.')) {
-          accum.tests[accum.tests.length - 1][accum.state].lines.push (line);
-        } else if (accum.state === 'input') {
-          //  A comment immediately following an input line is an output
-          //  line if and only if it contains non-whitespace characters.
-          const {lines} = accum.tests[accum.tests.length - 1].input;
-          if (contiguous (line) (lines) && text !== '') {
-            accum.tests[accum.tests.length - 1][accum.state = 'output'] =
-              {lines: [line], start};
+          const {input, outputs} = accum.tests[accum.tests.length - 1];
+          if (accum.state === 'input') {
+            input.lines.push (line);
+          } else {
+            outputs[outputs.length - 1].lines.push (line);
+          }
+        } else if (accum.state === 'input' || accum.state === 'outputs') {
+          const {input, outputs} = accum.tests[accum.tests.length - 1];
+          if (
+            //  A comment immediately following an input line is an output
+            //  line if and only if it contains non-whitespace characters.
+            contiguous (line)
+                       (input.lines.concat (outputs.flatMap (o => o.lines))) &&
+            text !== ''
+          ) {
+            accum.state = 'outputs';
+            outputs.push ({channel: null, lines: [line], start});
           } else {
             accum.state = 'open';
           }
@@ -197,7 +245,7 @@ const rewriteJs = sourceType => ({
     {tests: [], state: openingDelimiter == null ? 'open' : 'closed'}
   )
   .tests
-  .map (test => [test.input.start, wrapJs (sourceType) (test)]);
+  .map (test => [test.input.start, wrapJs (sourceType) (logFunctions) (test)]);
 
   return Z.sort (Z.concat (literalChunks, commentChunks))
          .map (([, text]) => text)
@@ -208,6 +256,7 @@ const rewriteCoffee = ({
   prefix,
   openingDelimiter,
   closingDelimiter,
+  logFunctions,
 }) => input => {
   const lines = input.match (/^.*(?=\n)/gm);
   const chunks = lines.reduce ((accum, text, idx) => {
@@ -227,8 +276,8 @@ const rewriteCoffee = ({
     isComment: false,
   });
 
-  const testChunks = chunks.commentChunks.map (commentChunk => {
-    const result = commentChunk.reduce ((accum, {number, text}) => {
+  const testChunks = chunks.commentChunks.map (commentChunk =>
+    commentChunk.reduce ((accum, {number, text}) => {
       const [, indent, uncommented] = text.match (/^([ \t]*)#(.*)$/);
       if (uncommented.startsWith (prefix)) {
         const unprefixed = uncommented
@@ -240,36 +289,43 @@ const rewriteCoffee = ({
         } else if (unprefixed === closingDelimiter) {
           accum.state = 'closed';
         } else if (unprefixed.startsWith ('>')) {
+          accum.state = 'input';
           accum.tests.push ({
             indent,
-            [accum.state = 'input']: {
+            input: {
               lines: [line],
             },
+            outputs: [],
           });
         } else if (unprefixed.startsWith ('.')) {
-          accum.tests[accum.tests.length - 1][accum.state].lines.push (
-            line
-          );
-        } else if (accum.state === 'input') {
-          //  A comment immediately following an input line is an output
-          //  line if and only if it contains non-whitespace characters.
-          const {lines} = accum.tests[accum.tests.length - 1].input;
-          if (contiguous (line) (lines) && unprefixed !== '') {
-            accum.tests[accum.tests.length - 1][accum.state = 'output'] = {
-              lines: [line],
-            };
+          const {input, outputs} = accum.tests[accum.tests.length - 1];
+          if (accum.state === 'input') {
+            input.lines.push (line);
+          } else {
+            outputs[outputs.length - 1].lines.push (line);
+          }
+        } else if (accum.state === 'input' || accum.state === 'outputs') {
+          const {input, outputs} = accum.tests[accum.tests.length - 1];
+          if (
+            //  A comment immediately following an input line is an output
+            //  line if and only if it contains non-whitespace characters.
+            contiguous (line)
+                       (input.lines
+                        .concat (outputs.flatMap (o => o.lines))) &&
+            unprefixed !== ''
+          ) {
+            accum.state = 'outputs';
+            outputs.push ({channel: null, lines: [line]});
           } else {
             accum.state = 'open';
           }
         }
       }
       return accum;
-    }, {state: openingDelimiter == null ? 'open' : 'closed', tests: []});
-
-    return result.tests.map (
-      test => indentN (test.indent.length) (wrapCoffee (test))
-    );
-  });
+    }, {state: openingDelimiter == null ? 'open' : 'closed', tests: []})
+    .tests
+    .map (wrapCoffee (logFunctions))
+  );
 
   return CoffeeScript.compile (
     chunks.literalChunks.reduce (
@@ -283,26 +339,7 @@ const rewriteCoffee = ({
   );
 };
 
-const run = queue =>
-  queue.flatMap (({input, output}) => {
-    const i = encase (input.thunk) ();
-    if (output == null) return [];
-    const o = encase (output.thunk) ();
-    const comparison = (
-      effect (o => effect (i => i.name === o.name &&
-                                i.message === (o.message || i.message) ?
-                                Correct (Failure (i)) :
-                                Incorrect (Failure (i)) (Failure (o)))
-                          (i => Incorrect (Success (i)) (Failure (o))))
-             (o => effect (i => Incorrect (Failure (i)) (Success (o)))
-                          (i => Z.equals (i, o) ?
-                                Correct (Success (i)) :
-                                Incorrect (Success (i)) (Success (o))))
-             (o)
-             (i)
-    );
-    return [{lines: {input: input.lines, output: output.lines}, comparison}];
-  });
+const sentinel = {};
 
 const readSourceFile = async path => (
   (await fs.readFile (path, 'utf8'))
@@ -332,7 +369,7 @@ const evaluateModule = moduleUrl => async source => {
     return module;
   });
   await module.evaluate ();
-  return run (queue);
+  return queue;
 };
 
 const evaluateScript = context => async source => {
@@ -340,7 +377,77 @@ const evaluateScript = context => async source => {
   const enqueue = io => { queue.push (io); };
   const __doctest = {enqueue, require};
   vm.runInNewContext (source, {...global, ...context, __doctest});
-  return run (queue);
+  return queue;
+};
+
+const run = channels => timeout => async queue => {
+  const tests = [];
+  for (const {input, outputs} of queue) {
+    const actuals = await new Promise (res => {
+      const actuals = [];
+      let open = true;
+      let job;
+
+      const done = () => {
+        open = false;
+        clearTimeout (job);
+        res (actuals);
+      };
+
+      const logFunctions = channels.map (channel => value => {
+        if (open) {
+          actuals.push (Success (Channel (channel) (value)));
+          clearTimeout (job);
+          job = setTimeout (done, timeout);
+        }
+      });
+
+      actuals.push (encase (input.thunk) (logFunctions));
+
+      job = setTimeout (done, timeout);
+    });
+
+    if (outputs.length === 0) continue;
+
+    const expecteds = [];
+    const logFunctions = channels.map (channel => value => ((
+      expecteds.push (Success (Channel (channel) (value))),
+      sentinel
+    )));
+    for (const output of outputs) {
+      const expected = encase (output.thunk) (logFunctions);
+      if (effect (_ => true) (({value}) => value !== sentinel) (expected)) {
+        expecteds.push (expected);
+      }
+    }
+    const isError = x => (
+      Object.prototype.toString.call (x) === '[object Error]'
+    );
+    const test = {
+      lines: {
+        input: input.lines,
+        output: outputs.flatMap (output => output.lines),
+      },
+      comparison: (
+        actuals.length === expecteds.length &&
+        actuals.every ((a, idx) =>
+          effect (a => effect (e => isError (a) && isError (e)
+                                    ? a.name === e.name &&
+                                      a.message === (e.message || a.message)
+                                    : Z.equals (a, e))
+                              (_ => false))
+                 (a => effect (_ => false)
+                              (e => Z.equals (a, e)))
+                 (a)
+                 (expecteds[idx])
+        )
+        ? Correct (actuals)
+        : Incorrect (actuals) (expecteds)
+      ),
+    };
+    tests.push (test);
+  }
+  return tests;
 };
 
 export default ({
@@ -349,17 +456,21 @@ export default ({
   prefix = '',
   openingDelimiter,
   closingDelimiter,
+  logFunctions = [],
+  timeout = logFunctions.length > 0 ? 100 : 0,
   print = false,
 }) => async path => {
   const __filename = resolve (process.cwd (), path);
   let context = {};
-  const options = {prefix, openingDelimiter, closingDelimiter};
+  const options = {prefix, openingDelimiter, closingDelimiter, logFunctions};
   switch (module) {
     case 'esm': {
       const rewrite = rewriteJs ('module');
       const source = rewrite (options) (await readSourceFile (path));
       if (print) return source;
-      return evaluateModule (url.pathToFileURL (__filename)) (source);
+      const moduleUrl = url.pathToFileURL (__filename);
+      const queue = await evaluateModule (moduleUrl) (source);
+      return run (logFunctions) (timeout) (queue);
     }
     case 'commonjs': {
       const exports = {};
@@ -371,7 +482,8 @@ export default ({
       const rewrite = coffee ? rewriteCoffee : rewriteJs ('script');
       const source = rewrite (options) (await readSourceFile (path));
       if (print) return source;
-      return evaluateScript (context) (source);
+      const queue = await evaluateScript (context) (source);
+      return run (logFunctions) (timeout) (queue);
     }
     default: {
       throw new Error (`Invalid module ${show (module)}`);
diff --git a/lib/program.js b/lib/program.js
index 42ae7b4..5d0ba74 100644
--- a/lib/program.js
+++ b/lib/program.js
@@ -1,4 +1,5 @@
 import program from 'commander';
+import Z from 'sanctuary-type-classes';
 
 import require from './require.js';
 
@@ -20,10 +21,20 @@ program
          'specify line preceding doctest block (e.g. "```javascript")')
 .option ('    --closing-delimiter <delimiter>',
          'specify line following doctest block (e.g. "```")')
+.option ('    --log-function <name>',
+         'expose a log function with the given name to your doctests' +
+         ' (can be specified multiple times)',
+         Z.append,
+         [])
+.option ('    --timeout <milliseconds>',
+         'specify an alternative log timeout time (defaults to 100)')
 .option ('-p, --print',
          'output the rewritten source without running tests')
 .option ('-s, --silent',
          'suppress output')
 .parse (process.argv);
 
+program.logFunctions = program.logFunction;
+delete program.logFunction;
+
 export default program;
diff --git a/test/bin/results.js b/test/bin/results.js
index 59b5892..5f54bdc 100644
--- a/test/bin/results.js
+++ b/test/bin/results.js
@@ -1,8 +1,8 @@
-export default ({Test, Line, Correct, Success}) => [
+export default ({Test, Line, Correct, Success, Result}) => [
 
   Test ('executable without file extension')
        ([Line (3) ('> identity(42)')])
        ([Line (4) ('42')])
-       (Correct (Success (42))),
+       (Correct ([Success (Result (42))])),
 
 ];
diff --git a/test/commonjs/__dirname/results.coffee.js b/test/commonjs/__dirname/results.coffee.js
index 7fc2e57..02f2558 100644
--- a/test/commonjs/__dirname/results.coffee.js
+++ b/test/commonjs/__dirname/results.coffee.js
@@ -1,18 +1,18 @@
-export default ({Test, Line, Correct, Success}) => [
+export default ({Test, Line, Correct, Success, Result}) => [
 
   Test ('__dirname is defined')
        ([Line (3) ('> typeof __dirname')])
        ([Line (4) ("'string'")])
-       (Correct (Success ('string'))),
+       (Correct ([Success (Result ('string'))])),
 
   Test ('__dirname is absolute')
        ([Line (8) ('> path.isAbsolute __dirname')])
        ([Line (9) ('true')])
-       (Correct (Success (true))),
+       (Correct ([Success (Result (true))])),
 
   Test ('__dirname is correct')
        ([Line (11) ('> path.relative process.cwd(), __dirname')])
        ([Line (12) ("'test/commonjs/__dirname'")])
-       (Correct (Success ('test/commonjs/__dirname'))),
+       (Correct ([Success (Result ('test/commonjs/__dirname'))])),
 
 ];
diff --git a/test/commonjs/__dirname/results.js b/test/commonjs/__dirname/results.js
index 1c10de9..90a1790 100644
--- a/test/commonjs/__dirname/results.js
+++ b/test/commonjs/__dirname/results.js
@@ -1,18 +1,18 @@
-export default ({Test, Line, Correct, Success}) => [
+export default ({Test, Line, Correct, Success, Result}) => [
 
   Test ('__dirname is defined')
        ([Line (3) ('> typeof __dirname')])
        ([Line (4) ("'string'")])
-       (Correct (Success ('string'))),
+       (Correct ([Success (Result ('string'))])),
 
   Test ('__dirname is absolute')
        ([Line (8) ('> path.isAbsolute (__dirname)')])
        ([Line (9) ('true')])
-       (Correct (Success (true))),
+       (Correct ([Success (Result (true))])),
 
   Test ('__dirname is correct')
        ([Line (11) ('> path.relative (process.cwd (), __dirname)')])
        ([Line (12) ("'test/commonjs/__dirname'")])
-       (Correct (Success ('test/commonjs/__dirname'))),
+       (Correct ([Success (Result ('test/commonjs/__dirname'))])),
 
 ];
diff --git a/test/commonjs/__doctest.require/results.js b/test/commonjs/__doctest.require/results.js
index 2c3f78b..0026af8 100644
--- a/test/commonjs/__doctest.require/results.js
+++ b/test/commonjs/__doctest.require/results.js
@@ -1,8 +1,8 @@
-export default ({Test, Line, Correct, Success}) => [
+export default ({Test, Line, Correct, Success, Result}) => [
 
   Test ('__doctest.require')
        ([Line (5) ("> (new url.URL ('https://sanctuary.js.org/')).hostname")])
        ([Line (6) ("'sanctuary.js.org'")])
-       (Correct (Success ('sanctuary.js.org'))),
+       (Correct ([Success (Result ('sanctuary.js.org'))])),
 
 ];
diff --git a/test/commonjs/__filename/results.coffee.js b/test/commonjs/__filename/results.coffee.js
index 236155f..cb85d41 100644
--- a/test/commonjs/__filename/results.coffee.js
+++ b/test/commonjs/__filename/results.coffee.js
@@ -1,18 +1,18 @@
-export default ({Test, Line, Correct, Success}) => [
+export default ({Test, Line, Correct, Success, Result}) => [
 
   Test ('__filename is defined')
        ([Line (3) ('> typeof __filename')])
        ([Line (4) ("'string'")])
-       (Correct (Success ('string'))),
+       (Correct ([Success (Result ('string'))])),
 
   Test ('__filename is absolute')
        ([Line (8) ('> path.isAbsolute __filename')])
        ([Line (9) ('true')])
-       (Correct (Success (true))),
+       (Correct ([Success (Result (true))])),
 
   Test ('__filename is correct')
        ([Line (11) ('> path.relative process.cwd(), __filename')])
        ([Line (12) ("'test/commonjs/__filename/index.coffee'")])
-       (Correct (Success ('test/commonjs/__filename/index.coffee'))),
+       (Correct ([Success (Result ('test/commonjs/__filename/index.coffee'))])),
 
 ];
diff --git a/test/commonjs/__filename/results.js b/test/commonjs/__filename/results.js
index 18e35cb..3451781 100644
--- a/test/commonjs/__filename/results.js
+++ b/test/commonjs/__filename/results.js
@@ -1,18 +1,18 @@
-export default ({Test, Line, Correct, Success}) => [
+export default ({Test, Line, Correct, Success, Result}) => [
 
   Test ('__filename is defined')
        ([Line (3) ('> typeof __filename')])
        ([Line (4) ("'string'")])
-       (Correct (Success ('string'))),
+       (Correct ([Success (Result ('string'))])),
 
   Test ('__filename is absolute')
        ([Line (8) ('> path.isAbsolute (__filename)')])
        ([Line (9) ('true')])
-       (Correct (Success (true))),
+       (Correct ([Success (Result (true))])),
 
   Test ('__filename is correct')
        ([Line (11) ('> path.relative (process.cwd (), __filename)')])
        ([Line (12) ("'test/commonjs/__filename/index.js'")])
-       (Correct (Success ('test/commonjs/__filename/index.js'))),
+       (Correct ([Success (Result ('test/commonjs/__filename/index.js'))])),
 
 ];
diff --git a/test/commonjs/exports/results.js b/test/commonjs/exports/results.js
index eba1f37..3c8c083 100644
--- a/test/commonjs/exports/results.js
+++ b/test/commonjs/exports/results.js
@@ -1,8 +1,8 @@
-export default ({Test, Line, Correct, Success}) => [
+export default ({Test, Line, Correct, Success, Result}) => [
 
   Test ('exports')
        ([Line (1) ('> exports.identity(42)')])
        ([Line (2) ('42')])
-       (Correct (Success (42))),
+       (Correct ([Success (Result (42))])),
 
 ];
diff --git a/test/commonjs/module.exports/results.js b/test/commonjs/module.exports/results.js
index c06f84b..5b9b2b7 100644
--- a/test/commonjs/module.exports/results.js
+++ b/test/commonjs/module.exports/results.js
@@ -1,8 +1,8 @@
-export default ({Test, Line, Correct, Success}) => [
+export default ({Test, Line, Correct, Success, Result}) => [
 
   Test ('module.exports')
        ([Line (1) ('> module.exports(42)')])
        ([Line (2) ('42')])
-       (Correct (Success (42))),
+       (Correct ([Success (Result (42))])),
 
 ];
diff --git a/test/commonjs/require/results.js b/test/commonjs/require/results.js
index a0085fa..16edd5e 100644
--- a/test/commonjs/require/results.js
+++ b/test/commonjs/require/results.js
@@ -1,8 +1,8 @@
-export default ({Test, Line, Correct, Success}) => [
+export default ({Test, Line, Correct, Success, Result}) => [
 
   Test ('require another CommonJS module')
        ([Line (1) ('> typeof $require("assert")')])
        ([Line (2) ('"function"')])
-       (Correct (Success ('function'))),
+       (Correct ([Success (Result ('function'))])),
 
 ];
diff --git a/test/commonjs/strict/results.js b/test/commonjs/strict/results.js
index 7477891..fcba63c 100644
--- a/test/commonjs/strict/results.js
+++ b/test/commonjs/strict/results.js
@@ -1,8 +1,8 @@
-export default ({Test, Line, Correct, Success}) => [
+export default ({Test, Line, Correct, Success, Result}) => [
 
   Test ("preserves 'use strict' directive")
        ([Line (3) ('> (function() { return this; }())')])
        ([Line (4) ('undefined')])
-       (Correct (Success (undefined))),
+       (Correct ([Success (Result (undefined))])),
 
 ];
diff --git a/test/contiguity/results.js b/test/contiguity/results.js
index c8a8f8d..04b9b5e 100644
--- a/test/contiguity/results.js
+++ b/test/contiguity/results.js
@@ -1,8 +1,8 @@
-export default ({Test, Line, Correct, Success}) => [
+export default ({Test, Line, Correct, Success, Result}) => [
 
   Test ('output line immediately following input line')
        ([Line (15) ('> zero (42)')])
        ([Line (16) ('0')])
-       (Correct (Success (0))),
+       (Correct ([Success (Result (0))])),
 
 ];
diff --git a/test/es2015/results.js b/test/es2015/results.js
index 1f3cb57..4ffbc20 100644
--- a/test/es2015/results.js
+++ b/test/es2015/results.js
@@ -1,28 +1,28 @@
-export default ({Test, Line, Correct, Success}) => [
+export default ({Test, Line, Correct, Success, Result}) => [
 
   Test ('seq.next().value')
        ([Line (12) ('> seq.next().value')])
        ([Line (13) ('1')])
-       (Correct (Success (1))),
+       (Correct ([Success (Result (1))])),
 
   Test ('seq.next().value')
        ([Line (14) ('> seq.next().value')])
        ([Line (15) ('1')])
-       (Correct (Success (1))),
+       (Correct ([Success (Result (1))])),
 
   Test ('seq.next().value')
        ([Line (16) ('> seq.next().value')])
        ([Line (17) ('2')])
-       (Correct (Success (2))),
+       (Correct ([Success (Result (2))])),
 
   Test ('seq.next().value')
        ([Line (18) ('> seq.next().value')])
        ([Line (19) ('3')])
-       (Correct (Success (3))),
+       (Correct ([Success (Result (3))])),
 
   Test ('seq.next().value')
        ([Line (20) ('> seq.next().value')])
        ([Line (21) ('5')])
-       (Correct (Success (5))),
+       (Correct ([Success (Result (5))])),
 
 ];
diff --git a/test/es2018/results.js b/test/es2018/results.js
index 990762f..01149ad 100644
--- a/test/es2018/results.js
+++ b/test/es2018/results.js
@@ -1,8 +1,8 @@
-export default ({Test, Line, Correct, Success}) => [
+export default ({Test, Line, Correct, Success, Result}) => [
 
   Test ('object spread syntax')
        ([Line (1) ('> {x: 0, ...{x: 1, y: 2, z: 3}, z: 4}')])
        ([Line (2) ('{x: 1, y: 2, z: 4}')])
-       (Correct (Success ({x: 1, y: 2, z: 4}))),
+       (Correct ([Success (Result ({x: 1, y: 2, z: 4}))])),
 
 ];
diff --git a/test/es2020/results.js b/test/es2020/results.js
index 9bde95c..b02071a 100644
--- a/test/es2020/results.js
+++ b/test/es2020/results.js
@@ -1,8 +1,8 @@
-export default ({Test, Line, Correct, Success}) => [
+export default ({Test, Line, Correct, Success, Result}) => [
 
   Test ('nullish coalescing operator')
        ([Line (1) ("> null ?? 'default'")])
        ([Line (2) ("'default'")])
-       (Correct (Success ('default'))),
+       (Correct ([Success (Result ('default'))])),
 
 ];
diff --git a/test/esm/async.js b/test/esm/async.js
new file mode 100644
index 0000000..da6f215
--- /dev/null
+++ b/test/esm/async.js
@@ -0,0 +1,7 @@
+// > ( stdout (1)
+// . , setTimeout (stdout, 1, 2)
+// . , stderr (3) )
+// stdout (1)
+// stderr (3)
+// undefined
+// stdout (2)
diff --git a/test/esm/globals/results.js b/test/esm/globals/results.js
index 103f345..d6a928c 100644
--- a/test/esm/globals/results.js
+++ b/test/esm/globals/results.js
@@ -1,8 +1,8 @@
-export default ({Test, Line, Correct, Success}) => [
+export default ({Test, Line, Correct, Success, Result}) => [
 
   Test ('setTimeout is defined')
        ([Line (1) ('> typeof setTimeout')])
        ([Line (2) ("'function'")])
-       (Correct (Success ('function'))),
+       (Correct ([Success (Result ('function'))])),
 
 ];
diff --git a/test/exceptions/index.js b/test/exceptions/index.js
index d56a5f8..1afa864 100644
--- a/test/exceptions/index.js
+++ b/test/exceptions/index.js
@@ -12,26 +12,29 @@
 // new Error('XXX')
 
 // > new Error('Invalid value')
-// ! Error: Invalid value
+// throw new Error('Invalid value')
 
 // > sqrt(-1)
 // new Error('Invalid value')
 
 // > 0..toString(1)
-// ! RangeError
+// throw new RangeError
 
 // > 0..toString(1)
-// ! Error
+// throw new Error
 
 // > sqrt(-1)
-// ! Error: Invalid value
+// throw new Error('Invalid value')
 
 // > sqrt(-1)
-// ! Error: XXX
+// throw new Error('XXX')
 
 // > 'foo' + 'bar'
 // foobar
 
+// > (() => { throw [1, 2, 3] })()
+// throw [1, 2, 3]
+
 var sqrt = function(n) {
   if (n >= 0) {
     return Math.sqrt(n);
diff --git a/test/exceptions/results.js b/test/exceptions/results.js
index e073d86..530cb05 100644
--- a/test/exceptions/results.js
+++ b/test/exceptions/results.js
@@ -1,66 +1,71 @@
-export default ({Test, Line, Incorrect, Correct, Failure, Success}) => [
+export default ({Test, Line, Incorrect, Correct, Failure, Success, Result}) => [
 
   Test ('input evaluates to Error with expected message')
        ([Line (2) ("> new Error('Invalid value')")])
        ([Line (3) ("new Error('Invalid value')")])
-       (Correct (Success (new Error ('Invalid value')))),
+       (Correct ([Success (Result (new Error ('Invalid value')))])),
 
   Test ('input evaluates to Error without expected message')
        ([Line (5) ('> new Error()')])
        ([Line (6) ("new Error('Invalid value')")])
-       (Incorrect (Success (new Error ()))
-                  (Success (new Error ('Invalid value')))),
+       (Incorrect ([Success (Result (new Error ()))])
+                  ([Success (Result (new Error ('Invalid value')))])),
 
   Test ('input evaluates to Error with unexpected message')
        ([Line (8) ("> new Error('Invalid value')")])
        ([Line (9) ('new Error()')])
-       (Incorrect (Success (new Error ('Invalid value')))
-                  (Success (new Error ()))),
+       (Incorrect ([Success (Result (new Error ('Invalid value')))])
+                  ([Success (Result (new Error ()))])),
 
   Test ('input evaluates to Error with unexpected message')
        ([Line (11) ("> new Error('Invalid value')")])
        ([Line (12) ("new Error('XXX')")])
-       (Incorrect (Success (new Error ('Invalid value')))
-                  (Success (new Error ('XXX')))),
+       (Incorrect ([Success (Result (new Error ('Invalid value')))])
+                  ([Success (Result (new Error ('XXX')))])),
 
   Test ('evaluating input does not throw expected exception')
        ([Line (14) ("> new Error('Invalid value')")])
-       ([Line (15) ('! Error: Invalid value')])
-       (Incorrect (Success (new Error ('Invalid value')))
-                  (Failure (new Error ('Invalid value')))),
+       ([Line (15) ("throw new Error('Invalid value')")])
+       (Incorrect ([Success (Result (new Error ('Invalid value')))])
+                  ([Failure (new Error ('Invalid value'))])),
 
   Test ('evaluating input throws unexpected exception')
        ([Line (17) ('> sqrt(-1)')])
        ([Line (18) ("new Error('Invalid value')")])
-       (Incorrect (Failure (new Error ('Invalid value')))
-                  (Success (new Error ('Invalid value')))),
+       (Incorrect ([Failure (new Error ('Invalid value'))])
+                  ([Success (Result (new Error ('Invalid value')))])),
 
   Test ('evaluating input throws exception as expected, of expected type')
        ([Line (20) ('> 0..toString(1)')])
-       ([Line (21) ('! RangeError')])
-       (Correct (Failure (new RangeError ('toString() radix argument must be between 2 and 36')))),
+       ([Line (21) ('throw new RangeError')])
+       (Correct ([Failure (new RangeError ('toString() radix argument must be between 2 and 36'))])),
 
   Test ('evaluating input throws exception as expected, of unexpected type')
        ([Line (23) ('> 0..toString(1)')])
-       ([Line (24) ('! Error')])
-       (Incorrect (Failure (new RangeError ('toString() radix argument must be between 2 and 36')))
-                  (Failure (new Error ()))),
+       ([Line (24) ('throw new Error')])
+       (Incorrect ([Failure (new RangeError ('toString() radix argument must be between 2 and 36'))])
+                  ([Failure (new Error ())])),
 
   Test ('evaluating input throws exception as expected, with expected message')
        ([Line (26) ('> sqrt(-1)')])
-       ([Line (27) ('! Error: Invalid value')])
-       (Correct (Failure (new Error ('Invalid value')))),
+       ([Line (27) ("throw new Error('Invalid value')")])
+       (Correct ([Failure (new Error ('Invalid value'))])),
 
   Test ('evaluating input throws exception as expected, with unexpected message')
        ([Line (29) ('> sqrt(-1)')])
-       ([Line (30) ('! Error: XXX')])
-       (Incorrect (Failure (new Error ('Invalid value')))
-                  (Failure (new Error ('XXX')))),
+       ([Line (30) ("throw new Error('XXX')")])
+       (Incorrect ([Failure (new Error ('Invalid value'))])
+                  ([Failure (new Error ('XXX'))])),
 
   Test ('evaluating output throws unexpected exception')
        ([Line (32) ("> 'foo' + 'bar'")])
        ([Line (33) ('foobar')])
-       (Incorrect (Success ('foobar'))
-                  (Failure (new ReferenceError ('foobar is not defined')))),
+       (Incorrect ([Success (Result ('foobar'))])
+                  ([Failure (new ReferenceError ('foobar is not defined'))])),
+
+  Test ('evaluating input throws non-Error exception as expected')
+       ([Line (35) ('> (() => { throw [1, 2, 3] })()')])
+       ([Line (36) ('throw [1, 2, 3]')])
+       (Correct ([Failure ([1, 2, 3])])),
 
 ];
diff --git a/test/fantasy-land/results.js b/test/fantasy-land/results.js
index e2dc03c..5ab1233 100644
--- a/test/fantasy-land/results.js
+++ b/test/fantasy-land/results.js
@@ -1,11 +1,11 @@
 import Absolute from './index.js';
 
 
-export default ({Test, Line, Correct, Success}) => [
+export default ({Test, Line, Correct, Success, Result}) => [
 
   Test ('uses Z.equals for equality checks')
        ([Line (1) ('> Absolute(-1)')])
        ([Line (2) ('Absolute(1)')])
-       (Correct (Success (Absolute (-1)))),
+       (Correct ([Success (Result (Absolute (-1)))])),
 
 ];
diff --git a/test/index.js b/test/index.js
index 544153d..4e7021e 100644
--- a/test/index.js
+++ b/test/index.js
@@ -9,6 +9,7 @@ import Z from 'sanctuary-type-classes';
 import {Incorrect, Correct} from '../lib/Comparison.js';
 import {Failure, Success} from '../lib/Effect.js';
 import {Line} from '../lib/Line.js';
+import {Result, Channel} from '../lib/Output.js';
 import doctest from '../lib/doctest.js';
 
 import resultsBin from './bin/results.js';
@@ -29,12 +30,18 @@ import resultsEsmGlobals from './esm/globals/results.js';
 import resultsExceptions from './exceptions/results.js';
 import resultsFantasyLand from './fantasy-land/results.js';
 import resultsLineEndings from './line-endings/results.js';
+import resultsLogging from './logging/results.js';
 import resultsSharedCoffee from './shared/results.coffee.js';
 import resultsSharedJs from './shared/results.js';
 import resultsStatements from './statements/results.js';
 import resultsTranscribe from './transcribe/results.js';
 
 
+const style = ([chunk, ...chunks], ...args) => chunks.reduce (
+  (text, chunk, idx) => `${text}\u001B[${args[idx]}m${chunk}`,
+  chunk
+);
+
 const eq = actual => expected => {
   strictEqual (show (actual), show (expected));
   strictEqual (Z.equals (actual, expected), true);
@@ -66,6 +73,8 @@ const dependencies = {
   Correct,
   Failure,
   Success,
+  Result,
+  Channel,
 };
 
 const testModule = (module, path, options) => {
@@ -218,6 +227,10 @@ testModule (resultsContiguity, 'test/contiguity/index.coffee', {
   coffee: true,
 });
 
+testModule (resultsLogging, 'test/logging/index.js', {
+  logFunctions: ['stdout', 'stderr'],
+});
+
 {
   const options = {module: 'esm', print: true};
   const path = 'test/esm/index.js';
@@ -231,22 +244,25 @@ __doctest.enqueue({
     lines: [
       {number: 3, text: "> toFahrenheit (0)"},
     ],
-    thunk: () => {
+    thunk: ([]) => {
       return (
         toFahrenheit (0)
       );
     },
   },
-  output: {
-    lines: [
-      {number: 4, text: "32"},
-    ],
-    thunk: () => {
-      return (
-        32
-      );
+  outputs: [
+    {
+      lines: [
+        {number: 4, text: "32"},
+      ],
+      channel: null,
+      thunk: ([]) => {
+        return (
+          32
+        );
+      },
     },
-  },
+  ],
 });
 
 
@@ -260,118 +276,334 @@ export function toFahrenheit(degreesCelsius) {
 
 testCommand ('bin/doctest', {
   status: 0,
-  stdout: '',
-  stderr: '',
+  stdout: style``,
+  stderr: style``,
 });
 
 testCommand ('bin/doctest --xxx', {
   status: 1,
-  stdout: '',
-  stderr: `error: unknown option \`--xxx'
+  stdout: style``,
+  stderr: style`error: unknown option \`--xxx'
 `,
 });
 
 testCommand ('bin/doctest test/shared/index.js', {
   status: 1,
-  stdout: `running doctests in test/shared/index.js...
-......x.x...........x........x
-FAIL: expected 5 on line 31 (got 4)
-FAIL: expected ! TypeError on line 38 (got 0)
-FAIL: expected 9.5 on line 97 (got 5)
-FAIL: expected "on automatic semicolon insertion" on line 155 (got "the rewriter should not rely")
+  stdout: style`
+Running doctests in ${1}test/shared/index.js${22}...
+
+${7}   30 ${0} ${34}> two + two${0}
+${7}   31 ${0} ${35}5${0}
+
+${34}4${0}
+${35}5${0}
+
+${7}   37 ${0} ${34}> [].length${0}
+${7}   38 ${0} ${35}throw new TypeError${0}
+
+${34}0${0}
+${35}${1}throw${22} new TypeError ("")${0}
+
+${7}   95 ${0} ${34}>10 -${0}
+${7}   96 ${0} ${34}..5${0}
+${7}   97 ${0} ${35}9.5${0}
+
+${34}5${0}
+${35}9.5${0}
+
+${7}  154 ${0} ${34}> "the rewriter should not rely"${0}
+${7}  155 ${0} ${35}"on automatic semicolon insertion"${0}
+
+${34}"the rewriter should not rely"${0}
+${35}"on automatic semicolon insertion"${0}
+
 `,
-  stderr: '',
+  stderr: style``,
 });
 
 testCommand ('bin/doctest --coffee test/shared/index.coffee', {
   status: 1,
-  stdout: `running doctests in test/shared/index.coffee...
-......x.x...........x.....
-FAIL: expected 5 on line 31 (got 4)
-FAIL: expected ! TypeError on line 38 (got 0)
-FAIL: expected 9.5 on line 97 (got 5)
+  stdout: style`
+Running doctests in ${1}test/shared/index.coffee${22}...
+
+${7}   30 ${0} ${34}> two + two${0}
+${7}   31 ${0} ${35}5${0}
+
+${34}4${0}
+${35}5${0}
+
+${7}   37 ${0} ${34}> [].length${0}
+${7}   38 ${0} ${35}throw new TypeError${0}
+
+${34}0${0}
+${35}${1}throw${22} new TypeError ("")${0}
+
+${7}   95 ${0} ${34}>10 -${0}
+${7}   96 ${0} ${34}..5${0}
+${7}   97 ${0} ${35}9.5${0}
+
+${34}5${0}
+${35}9.5${0}
+
+`,
+  stderr: style``,
+});
+
+testCommand ('bin/doctest test/exceptions/index.js', {
+  status: 1,
+  stdout: style`
+Running doctests in ${1}test/exceptions/index.js${22}...
+
+${7}    5 ${0} ${34}> new Error()${0}
+${7}    6 ${0} ${35}new Error('Invalid value')${0}
+
+${34}new Error ("")${0}
+${35}new Error ("Invalid value")${0}
+
+${7}    8 ${0} ${34}> new Error('Invalid value')${0}
+${7}    9 ${0} ${35}new Error()${0}
+
+${34}new Error ("Invalid value")${0}
+${35}new Error ("")${0}
+
+${7}   11 ${0} ${34}> new Error('Invalid value')${0}
+${7}   12 ${0} ${35}new Error('XXX')${0}
+
+${34}new Error ("Invalid value")${0}
+${35}new Error ("XXX")${0}
+
+${7}   14 ${0} ${34}> new Error('Invalid value')${0}
+${7}   15 ${0} ${35}throw new Error('Invalid value')${0}
+
+${34}new Error ("Invalid value")${0}
+${35}${1}throw${22} new Error ("Invalid value")${0}
+
+${7}   17 ${0} ${34}> sqrt(-1)${0}
+${7}   18 ${0} ${35}new Error('Invalid value')${0}
+
+${34}${1}throw${22} new Error ("Invalid value")${0}
+${35}new Error ("Invalid value")${0}
+
+${7}   23 ${0} ${34}> 0..toString(1)${0}
+${7}   24 ${0} ${35}throw new Error${0}
+
+${34}${1}throw${22} new RangeError ("toString() radix argument must be between 2 and 36")${0}
+${35}${1}throw${22} new Error ("")${0}
+
+${7}   29 ${0} ${34}> sqrt(-1)${0}
+${7}   30 ${0} ${35}throw new Error('XXX')${0}
+
+${34}${1}throw${22} new Error ("Invalid value")${0}
+${35}${1}throw${22} new Error ("XXX")${0}
+
+${7}   32 ${0} ${34}> 'foo' + 'bar'${0}
+${7}   33 ${0} ${35}foobar${0}
+
+${34}"foobar"${0}
+${35}${1}throw${22} new ReferenceError ("foobar is not defined")${0}
+
 `,
-  stderr: '',
+  stderr: style``,
 });
 
 testCommand ('bin/doctest --silent test/shared/index.js', {
   status: 1,
-  stdout: '',
-  stderr: '',
+  stdout: style``,
+  stderr: style``,
+});
+
+testCommand ('bin/doctest --module xxx file.js', {
+  status: 1,
+  stdout: style``,
+  stderr: style`Error: Invalid module "xxx"
+`,
 });
 
 testCommand ('bin/doctest test/bin/executable', {
   status: 0,
-  stdout: `running doctests in test/bin/executable...
-.
+  stdout: style`
+Running doctests in ${1}test/bin/executable${22}...
+
 `,
-  stderr: '',
+  stderr: style``,
 });
 
-testCommand ('bin/doctest --module xxx file.js', {
+testCommand ("bin/doctest --prefix . --opening-delimiter '```javascript' --closing-delimiter '```' test/transcribe/index.js", {
+  status: 0,
+  stdout: style`
+Running doctests in ${1}test/transcribe/index.js${22}...
+
+`,
+  stderr: style``,
+});
+
+testCommand ("bin/doctest --coffee --prefix . --opening-delimiter '```coffee' --closing-delimiter '```' test/transcribe/index.coffee", {
+  status: 0,
+  stdout: style`
+Running doctests in ${1}test/transcribe/index.coffee${22}...
+
+`,
+  stderr: style``,
+});
+
+testCommand ('bin/doctest --log-function stdout --log-function stderr test/shared/async.js', {
+  status: 0,
+  stdout: style`
+Running doctests in ${1}test/shared/async.js${22}...
+
+`,
+  stderr: style``,
+});
+
+testCommand ('bin/doctest --module commonjs --log-function stdout --log-function stderr test/shared/async.js', {
+  status: 0,
+  stdout: style`
+Running doctests in ${1}test/shared/async.js${22}...
+
+`,
+  stderr: style``,
+});
+
+testCommand ('bin/doctest --coffee --log-function stdout --log-function stderr test/shared/async.coffee', {
+  status: 0,
+  stdout: style`
+Running doctests in ${1}test/shared/async.coffee${22}...
+
+`,
+  stderr: style``,
+});
+
+testCommand ('bin/doctest --log-function stdout --log-function stderr test/logging/index.js', {
   status: 1,
-  stdout: '',
-  stderr: `Error: Invalid module "xxx"
+  stdout: style`
+Running doctests in ${1}test/logging/index.js${22}...
+
+${7}   29 ${0} ${34}> (stdout (1), 3)${0}
+${7}   30 ${0} ${35}stdout (1)${0}
+${7}   31 ${0} ${35}stdout (2)${0}
+${7}   32 ${0} ${35}return 3${0}
+
+${34}${1}stdout${22} (1)${0}
+${34}3${0}
+${35}${1}stdout${22} (1)${0}
+${35}${1}stdout${22} (2)${0}
+${35}3${0}
+
+${7}   36 ${0} ${34}> (stdout (1), stdout (2), 3)${0}
+${7}   37 ${0} ${35}stdout (1)${0}
+${7}   38 ${0} ${35}return 3${0}
+
+${34}${1}stdout${22} (1)${0}
+${34}${1}stdout${22} (2)${0}
+${34}3${0}
+${35}${1}stdout${22} (1)${0}
+${35}3${0}
+
+${7}   42 ${0} ${34}> (stdout (1), stdout (2), 3)${0}
+${7}   43 ${0} ${35}stdout (2)${0}
+${7}   44 ${0} ${35}stdout (1)${0}
+${7}   45 ${0} ${35}return 3${0}
+
+${34}${1}stdout${22} (1)${0}
+${34}${1}stdout${22} (2)${0}
+${34}3${0}
+${35}${1}stdout${22} (2)${0}
+${35}${1}stdout${22} (1)${0}
+${35}3${0}
+
+${7}   49 ${0} ${34}> (stdout (1), stdout (2), 3)${0}
+${7}   50 ${0} ${35}stdout (1)${0}
+${7}   51 ${0} ${35}stderr (2)${0}
+${7}   52 ${0} ${35}return 3${0}
+
+${34}${1}stdout${22} (1)${0}
+${34}${1}stdout${22} (2)${0}
+${34}3${0}
+${35}${1}stdout${22} (1)${0}
+${35}${1}stderr${22} (2)${0}
+${35}3${0}
+
+${7}   56 ${0} ${34}> (setTimeout (stdout, 125, 1), 2)${0}
+${7}   57 ${0} ${35}return 2${0}
+${7}   58 ${0} ${35}stdout (1)${0}
+
+${34}2${0}
+${35}2${0}
+${35}${1}stdout${22} (1)${0}
+
 `,
+  stderr: style``,
 });
 
 testCommand ('bin/doctest --module esm lib/doctest.js', {
   status: 0,
-  stdout: `running doctests in lib/doctest.js...
+  stdout: style`
+Running doctests in ${1}lib/doctest.js${22}...
 
 `,
-  stderr: '',
+  stderr: style``,
 });
 
 testCommand ('bin/doctest --module esm test/esm/index.js', {
   status: 0,
-  stdout: `running doctests in test/esm/index.js...
-.
+  stdout: style`
+Running doctests in ${1}test/esm/index.js${22}...
+
 `,
-  stderr: '',
+  stderr: style``,
 });
 
 testCommand ('bin/doctest --module esm test/esm/dependencies.js', {
   status: 0,
-  stdout: `running doctests in test/esm/dependencies.js...
-.
+  stdout: style`
+Running doctests in ${1}test/esm/dependencies.js${22}...
+
 `,
-  stderr: '',
+  stderr: style``,
 });
 
 testCommand ('bin/doctest --module esm test/esm/incorrect.js', {
   status: 1,
-  stdout: `running doctests in test/esm/incorrect.js...
-x
-FAIL: expected 32 on line 4 (got "0°F")
+  stdout: style`
+Running doctests in ${1}test/esm/incorrect.js${22}...
+
+${7}    3 ${0} ${34}> toFahrenheit (0)${0}
+${7}    4 ${0} ${35}32${0}
+
+${34}"0°F"${0}
+${35}32${0}
+
 `,
-  stderr: '',
+  stderr: style``,
 });
 
 testCommand ('bin/doctest --print test/commonjs/exports/index.js', {
   status: 0,
-  stdout: `
+  stdout: style`
 __doctest.enqueue({
   input: {
     lines: [
       {number: 1, text: "> exports.identity(42)"},
     ],
-    thunk: () => {
+    thunk: ([]) => {
       return (
         exports.identity(42)
       );
     },
   },
-  output: {
-    lines: [
-      {number: 2, text: "42"},
-    ],
-    thunk: () => {
-      return (
-        42
-      );
+  outputs: [
+    {
+      lines: [
+        {number: 2, text: "42"},
+      ],
+      channel: null,
+      thunk: ([]) => {
+        return (
+          42
+        );
+      },
     },
-  },
+  ],
 });
 
 
@@ -379,33 +611,36 @@ exports.identity = function(x) {
   return x;
 };
 `,
-  stderr: '',
+  stderr: style``,
 });
 
 testCommand ('bin/doctest --print --module commonjs test/commonjs/exports/index.js', {
   status: 0,
-  stdout: `
+  stdout: style`
 __doctest.enqueue({
   input: {
     lines: [
       {number: 1, text: "> exports.identity(42)"},
     ],
-    thunk: () => {
+    thunk: ([]) => {
       return (
         exports.identity(42)
       );
     },
   },
-  output: {
-    lines: [
-      {number: 2, text: "42"},
-    ],
-    thunk: () => {
-      return (
-        42
-      );
+  outputs: [
+    {
+      lines: [
+        {number: 2, text: "42"},
+      ],
+      channel: null,
+      thunk: ([]) => {
+        return (
+          42
+        );
+      },
     },
-  },
+  ],
 });
 
 
@@ -413,5 +648,5 @@ exports.identity = function(x) {
   return x;
 };
 `,
-  stderr: '',
+  stderr: style``,
 });
diff --git a/test/line-endings/results.js b/test/line-endings/results.js
index 1c5a3db..5051386 100644
--- a/test/line-endings/results.js
+++ b/test/line-endings/results.js
@@ -1,8 +1,8 @@
-export default ({Test, Line, Correct, Success}) => [
+export default ({Test, Line, Correct, Success, Result}) => [
 
   Test ('correct line number reported irrespective of line endings')
        ([Line (1) ('> 2 * 3 * 7')])
        ([Line (2) ('42')])
-       (Correct (Success (42))),
+       (Correct ([Success (Result (42))])),
 
 ];
diff --git a/test/logging/index.js b/test/logging/index.js
new file mode 100644
index 0000000..9257484
--- /dev/null
+++ b/test/logging/index.js
@@ -0,0 +1,64 @@
+// > function crash() { throw new Error ('') }
+
+// Synchronous log with output
+//
+// > (stdout (1), 2)
+// stdout (1)
+// return 2
+
+// Synchronous log with exception
+//
+// > (stdout (1), crash ())
+// stdout (1)
+// throw new Error ('')
+
+// Asynchronous log with output
+//
+// > (setImmediate (stdout, 1), 2)
+// return 2
+// stdout (1)
+
+// Asynchronous log with exception
+//
+// > (setImmediate (stdout, 1), crash ())
+// throw new Error ('')
+// stdout (1)
+
+// Failure due to not enough output
+//
+// > (stdout (1), 3)
+// stdout (1)
+// stdout (2)
+// return 3
+
+// Failure due to too much output
+//
+// > (stdout (1), stdout (2), 3)
+// stdout (1)
+// return 3
+
+// Failure due to incorrectly ordered output
+//
+// > (stdout (1), stdout (2), 3)
+// stdout (2)
+// stdout (1)
+// return 3
+
+// Failure due to output on the wrong channel
+//
+// > (stdout (1), stdout (2), 3)
+// stdout (1)
+// stderr (2)
+// return 3
+
+// Failure due to timing out
+//
+// > (setTimeout (stdout, 125, 1), 2)
+// return 2
+// stdout (1)
+
+// Success after a previous timeout
+//
+// > (setTimeout (stdout, 75, 1), 2)
+// return 2
+// stdout (1)
diff --git a/test/logging/results.js b/test/logging/results.js
new file mode 100644
index 0000000..ed47097
--- /dev/null
+++ b/test/logging/results.js
@@ -0,0 +1,91 @@
+export default ({Test, Line, Incorrect, Correct, Failure, Success, Result, Channel}) => [
+
+  Test ('synchronous log with output')
+       ([Line (5) ('> (stdout (1), 2)')])
+       ([Line (6) ('stdout (1)'),
+         Line (7) ('return 2')])
+       (Correct ([Success (Channel ('stdout') (1)),
+                  Success (Result (2))])),
+
+  Test ('synchronous log with exception')
+       ([Line (11) ('> (stdout (1), crash ())')])
+       ([Line (12) ('stdout (1)'),
+         Line (13) ("throw new Error ('')")])
+       (Correct ([Success (Channel ('stdout') (1)),
+                  Failure (new Error (''))])),
+
+  Test ('asynchronous log with output')
+       ([Line (17) ('> (setImmediate (stdout, 1), 2)')])
+       ([Line (18) ('return 2'),
+         Line (19) ('stdout (1)')])
+       (Correct ([Success (Result (2)),
+                  Success (Channel ('stdout') (1))])),
+
+  Test ('asynchronous log with exception')
+       ([Line (23) ('> (setImmediate (stdout, 1), crash ())')])
+       ([Line (24) ("throw new Error ('')"),
+         Line (25) ('stdout (1)')])
+       (Correct ([Failure (new Error ('')),
+                  Success (Channel ('stdout') (1))])),
+
+  Test ('failure due to not enough output')
+       ([Line (29) ('> (stdout (1), 3)')])
+       ([Line (30) ('stdout (1)'),
+         Line (31) ('stdout (2)'),
+         Line (32) ('return 3')])
+       (Incorrect ([Success (Channel ('stdout') (1)),
+                    Success (Result (3))])
+                  ([Success (Channel ('stdout') (1)),
+                    Success (Channel ('stdout') (2)),
+                    Success (Result (3))])),
+
+  Test ('failure due to too much output')
+       ([Line (36) ('> (stdout (1), stdout (2), 3)')])
+       ([Line (37) ('stdout (1)'),
+         Line (38) ('return 3')])
+       (Incorrect ([Success (Channel ('stdout') (1)),
+                    Success (Channel ('stdout') (2)),
+                    Success (Result (3))])
+                  ([Success (Channel ('stdout') (1)),
+                    Success (Result (3))])),
+
+  Test ('failure due to incorrectly ordered output')
+       ([Line (42) ('> (stdout (1), stdout (2), 3)')])
+       ([Line (43) ('stdout (2)'),
+         Line (44) ('stdout (1)'),
+         Line (45) ('return 3')])
+       (Incorrect ([Success (Channel ('stdout') (1)),
+                    Success (Channel ('stdout') (2)),
+                    Success (Result (3))])
+                  ([Success (Channel ('stdout') (2)),
+                    Success (Channel ('stdout') (1)),
+                    Success (Result (3))])),
+
+  Test ('failure due to output on the wrong channel')
+       ([Line (49) ('> (stdout (1), stdout (2), 3)')])
+       ([Line (50) ('stdout (1)'),
+         Line (51) ('stderr (2)'),
+         Line (52) ('return 3')])
+       (Incorrect ([Success (Channel ('stdout') (1)),
+                    Success (Channel ('stdout') (2)),
+                    Success (Result (3))])
+                  ([Success (Channel ('stdout') (1)),
+                    Success (Channel ('stderr') (2)),
+                    Success (Result (3))])),
+
+  Test ('failure due to timing out')
+       ([Line (56) ('> (setTimeout (stdout, 125, 1), 2)')])
+       ([Line (57) ('return 2'),
+         Line (58) ('stdout (1)')])
+       (Incorrect ([Success (Result (2))])
+                  ([Success (Result (2)),
+                    Success (Channel ('stdout') (1))])),
+
+  Test ('success after a previous timeout')
+       ([Line (62) ('> (setTimeout (stdout, 75, 1), 2)')])
+       ([Line (63) ('return 2'),
+         Line (64) ('stdout (1)')])
+       (Correct ([Success (Result (2)),
+                  Success (Channel ('stdout') (1))])),
+
+];
diff --git a/test/shared/async.coffee b/test/shared/async.coffee
new file mode 100644
index 0000000..209a1d4
--- /dev/null
+++ b/test/shared/async.coffee
@@ -0,0 +1,7 @@
+# > stdout 1;
+# . setTimeout stdout, 50, 2;
+# . stderr 3;
+# stdout 1
+# stderr 3
+# undefined
+# stdout 2
diff --git a/test/shared/async.js b/test/shared/async.js
new file mode 100644
index 0000000..a5e0a51
--- /dev/null
+++ b/test/shared/async.js
@@ -0,0 +1,7 @@
+// > ( stdout (1)
+// . , setTimeout (stdout, 50, 2)
+// . , stderr (3) )
+// stdout (1)
+// stderr (3)
+// undefined
+// stdout (2)
diff --git a/test/shared/index.coffee b/test/shared/index.coffee
index dca6d05..c8b328e 100644
--- a/test/shared/index.coffee
+++ b/test/shared/index.coffee
@@ -32,10 +32,10 @@ do ->
 
   8: 'RangeError captured and reported'
   # > 0.toString 1
-  # ! RangeError
+  # throw new RangeError
   9: 'TypeError expected but not reported'
   # > [].length
-  # ! TypeError
+  # throw new TypeError
 
   10: 'function accessible before declaration'
   # > double(6)
diff --git a/test/shared/index.js b/test/shared/index.js
index cad5eb1..7cec857 100644
--- a/test/shared/index.js
+++ b/test/shared/index.js
@@ -32,10 +32,10 @@ global = 'global'
 
   8, 'RangeError captured and reported'
   // > 0..toString(1)
-  // ! RangeError
+  // throw new RangeError
   9, 'TypeError expected but not reported'
   // > [].length
-  // ! TypeError
+  // throw new TypeError
 
   10, 'function accessible before declaration'
   // > double(6)
@@ -64,7 +64,7 @@ global = 'global'
   // .  7,8,9]
   // [1,2,3,4,5,6,7,8,9]
   14, 'multiline assignment'
-  // > string = "input " +
+  // > var string = "input " +
   // . "may span many " +
   // . "lines"
   // > string
diff --git a/test/shared/results.coffee.js b/test/shared/results.coffee.js
index 86b9414..9508d6e 100644
--- a/test/shared/results.coffee.js
+++ b/test/shared/results.coffee.js
@@ -1,115 +1,115 @@
-export default ({Test, Line, Incorrect, Correct, Failure, Success}) => [
+export default ({Test, Line, Incorrect, Correct, Failure, Success, Result}) => [
 
   Test ('global variable accessible in outer scope')
        ([Line (2) ('> global')])
        ([Line (3) ('"global"')])
-       (Correct (Success ('global'))),
+       (Correct ([Success (Result ('global'))])),
 
   Test ('global variable accessible in inner scope')
        ([Line (9) ('> global')])
        ([Line (10) ('"global"')])
-       (Correct (Success ('global'))),
+       (Correct ([Success (Result ('global'))])),
 
   Test ('local variable referenced, not shadowed global')
        ([Line (13) ('> global')])
        ([Line (14) ('"shadowed"')])
-       (Correct (Success ('shadowed'))),
+       (Correct ([Success (Result ('shadowed'))])),
 
   Test ('local variable accessible before declaration')
        ([Line (19) ('> one * two')])
        ([Line (20) ('2')])
-       (Correct (Success (2))),
+       (Correct ([Success (Result (2))])),
 
   Test ('assignment is an expression')
        ([Line (24) ('> @three = one + two')])
        ([Line (25) ('3')])
-       (Correct (Success (3))),
+       (Correct ([Success (Result (3))])),
 
   Test ('variable declared in doctest remains accessible')
        ([Line (27) ('> [one, two, three]')])
        ([Line (28) ('[1, 2, 3]')])
-       (Correct (Success ([1, 2, 3]))),
+       (Correct ([Success (Result ([1, 2, 3]))])),
 
   Test ('arithmetic error reported')
        ([Line (30) ('> two + two')])
        ([Line (31) ('5')])
-       (Incorrect (Success (4))
-                  (Success (5))),
+       (Incorrect ([Success (Result (4))])
+                  ([Success (Result (5))])),
 
   Test ('RangeError captured and reported')
        ([Line (34) ('> 0.toString 1')])
-       ([Line (35) ('! RangeError')])
-       (Correct (Failure (new RangeError ('toString() radix argument must be between 2 and 36')))),
+       ([Line (35) ('throw new RangeError')])
+       (Correct ([Failure (new RangeError ('toString() radix argument must be between 2 and 36'))])),
 
   Test ('TypeError expected but not reported')
        ([Line (37) ('> [].length')])
-       ([Line (38) ('! TypeError')])
-       (Incorrect (Success (0))
-                  (Failure (new TypeError ()))),
+       ([Line (38) ('throw new TypeError')])
+       (Incorrect ([Success (Result (0))])
+                  ([Failure (new TypeError ())])),
 
   Test ('function accessible before declaration')
        ([Line (41) ('> double(6)')])
        ([Line (42) ('12')])
-       (Correct (Success (12))),
+       (Correct ([Success (Result (12))])),
 
   Test ('NaN can be used as expected result')
        ([Line (44) ('> double()')])
        ([Line (45) ('NaN')])
-       (Correct (Success (NaN))),
+       (Correct ([Success (Result (NaN))])),
 
   Test ('function accessible after declaration')
        ([Line (52) ('> double.call(null, 2)')])
        ([Line (53) ('4')])
-       (Correct (Success (4))),
+       (Correct ([Success (Result (4))])),
 
   Test ('multiline input')
        ([Line (62) ('> [1,2,3,'),
          Line (63) ('.  4,5,6,'),
          Line (64) ('.  7,8,9]')])
        ([Line (65) ('[1,2,3,4,5,6,7,8,9]')])
-       (Correct (Success ([1, 2, 3, 4, 5, 6, 7, 8, 9]))),
+       (Correct ([Success (Result ([1, 2, 3, 4, 5, 6, 7, 8, 9]))])),
 
   Test ('multiline assignment')
        ([Line (70) ('> string')])
        ([Line (71) ('"input may span many lines"')])
-       (Correct (Success ('input may span many lines'))),
+       (Correct ([Success (Result ('input may span many lines'))])),
 
   Test ("spaces following '#' and '>' are optional")
        ([Line (74) ('>"no spaces"')])
        ([Line (75) ('"no spaces"')])
-       (Correct (Success ('no spaces'))),
+       (Correct ([Success (Result ('no spaces'))])),
 
   Test ('indented doctest')
        ([Line (77) ('> "Docco-compatible whitespace"')])
        ([Line (78) ('"Docco-compatible whitespace"')])
-       (Correct (Success ('Docco-compatible whitespace'))),
+       (Correct ([Success (Result ('Docco-compatible whitespace'))])),
 
   Test ("'>' in doctest")
        ([Line (80) ('> 2 > 1')])
        ([Line (81) ('true')])
-       (Correct (Success (true))),
+       (Correct ([Success (Result (true))])),
 
   Test ('comment on input line')
        ([Line (84) ('> "foo" + "bar" # comment')])
        ([Line (85) ('"foobar"')])
-       (Correct (Success ('foobar'))),
+       (Correct ([Success (Result ('foobar'))])),
 
   Test ('comment on output line')
        ([Line (87) ('> 5 * 5')])
        ([Line (88) ('25 # comment')])
-       (Correct (Success (25))),
+       (Correct ([Success (Result (25))])),
 
   Test ('variable in creation context is not accessible')
        ([Line (91) ('> typeof Z')])
        ([Line (92) ('"undefined"')])
-       (Correct (Success ('undefined'))),
+       (Correct ([Success (Result ('undefined'))])),
 
   Test ("'.' should not follow leading '.' in multiline expressions")
        ([Line (95) ('>10 -'),
          Line (96) ('..5')])
        ([Line (97) ('9.5')])
-       (Incorrect (Success (5))
-                  (Success (9.5))),
+       (Incorrect ([Success (Result (5))])
+                  ([Success (Result (9.5))])),
 
   Test ("wrapped lines may begin with more than one '.'")
        ([Line (100) ('> 1000 +'),
@@ -118,12 +118,12 @@ export default ({Test, Line, Incorrect, Correct, Failure, Success}) => [
          Line (103) ('.... 4 +'),
          Line (104) ('..... .5')])
        ([Line (105) ('1234.5')])
-       (Correct (Success (1234.5))),
+       (Correct ([Success (Result (1234.5))])),
 
   Test ('multiline comment')
        ([Line (109) ('> 3 ** 3 - 2 ** 2')])
        ([Line (110) ('23')])
-       (Correct (Success (23))),
+       (Correct ([Success (Result (23))])),
 
   Test ('multiline comment with wrapped input')
        ([Line (115) ('> (["foo", "bar", "baz"]'),
@@ -131,14 +131,14 @@ export default ({Test, Line, Incorrect, Correct, Failure, Success}) => [
          Line (117) ('.  .join(" ")'),
          Line (118) ('.  .toUpperCase())')])
        ([Line (119) ('"FOO BAR"')])
-       (Correct (Success ('FOO BAR'))),
+       (Correct ([Success (Result ('FOO BAR'))])),
 
   Test ('multiline output')
        ([Line (139) ('> ["foo", "bar", "baz"]')])
        ([Line (140) ('[ "foo"'),
          Line (141) ('. "bar"'),
          Line (142) ('. "baz" ]')])
-       (Correct (Success (['foo', 'bar', 'baz']))),
+       (Correct ([Success (Result (['foo', 'bar', 'baz']))])),
 
   Test ('multiline input with multiline output')
        ([Line (145) ('> ["foo", "bar", "baz"]'),
@@ -148,6 +148,6 @@ export default ({Test, Line, Incorrect, Correct, Failure, Success}) => [
        ([Line (149) ('[ "FOO"'),
          Line (150) ('. "BAR"'),
          Line (151) ('. "BAZ" ]')])
-       (Correct (Success (['FOO', 'BAR', 'BAZ']))),
+       (Correct ([Success (Result (['FOO', 'BAR', 'BAZ']))])),
 
 ];
diff --git a/test/shared/results.js b/test/shared/results.js
index 7fca7e7..380cab8 100644
--- a/test/shared/results.js
+++ b/test/shared/results.js
@@ -1,115 +1,115 @@
-export default ({Test, Line, Incorrect, Correct, Failure, Success}) => [
+export default ({Test, Line, Incorrect, Correct, Failure, Success, Result}) => [
 
   Test ('global variable accessible in outer scope')
        ([Line (2) ('> global')])
        ([Line (3) ('"global"')])
-       (Correct (Success ('global'))),
+       (Correct ([Success (Result ('global'))])),
 
   Test ('global variable accessible in inner scope')
        ([Line (9) ('> global')])
        ([Line (10) ('"global"')])
-       (Correct (Success ('global'))),
+       (Correct ([Success (Result ('global'))])),
 
   Test ('local variable referenced, not shadowed global')
        ([Line (13) ('> global')])
        ([Line (14) ('"shadowed"')])
-       (Correct (Success ('shadowed'))),
+       (Correct ([Success (Result ('shadowed'))])),
 
   Test ('local variable accessible before declaration')
        ([Line (19) ('> one * two')])
        ([Line (20) ('2')])
-       (Correct (Success (2))),
+       (Correct ([Success (Result (2))])),
 
   Test ('assignment is an expression')
        ([Line (24) ('> three = one + two')])
        ([Line (25) ('3')])
-       (Correct (Success (3))),
+       (Correct ([Success (Result (3))])),
 
   Test ('variable declared in doctest remains accessible')
        ([Line (27) ('> [one, two, three]')])
        ([Line (28) ('[1, 2, 3]')])
-       (Correct (Success ([1, 2, 3]))),
+       (Correct ([Success (Result ([1, 2, 3]))])),
 
   Test ('arithmetic error reported')
        ([Line (30) ('> two + two')])
        ([Line (31) ('5')])
-       (Incorrect (Success (4))
-                  (Success (5))),
+       (Incorrect ([Success (Result (4))])
+                  ([Success (Result (5))])),
 
   Test ('RangeError captured and reported')
        ([Line (34) ('> 0..toString(1)')])
-       ([Line (35) ('! RangeError')])
-       (Correct (Failure (new RangeError ('toString() radix argument must be between 2 and 36')))),
+       ([Line (35) ('throw new RangeError')])
+       (Correct ([Failure (new RangeError ('toString() radix argument must be between 2 and 36'))])),
 
   Test ('TypeError expected but not reported')
        ([Line (37) ('> [].length')])
-       ([Line (38) ('! TypeError')])
-       (Incorrect (Success (0))
-                  (Failure (new TypeError ()))),
+       ([Line (38) ('throw new TypeError')])
+       (Incorrect ([Success (Result (0))])
+                  ([Failure (new TypeError ())])),
 
   Test ('function accessible before declaration')
        ([Line (41) ('> double(6)')])
        ([Line (42) ('12')])
-       (Correct (Success (12))),
+       (Correct ([Success (Result (12))])),
 
   Test ('NaN can be used as expected result')
        ([Line (44) ('> double()')])
        ([Line (45) ('NaN')])
-       (Correct (Success (NaN))),
+       (Correct ([Success (Result (NaN))])),
 
   Test ('function accessible after declaration')
        ([Line (52) ('> double.call(null, 2)')])
        ([Line (53) ('4')])
-       (Correct (Success (4))),
+       (Correct ([Success (Result (4))])),
 
   Test ('multiline input')
        ([Line (62) ('> [1,2,3,'),
          Line (63) ('.  4,5,6,'),
          Line (64) ('.  7,8,9]')])
        ([Line (65) ('[1,2,3,4,5,6,7,8,9]')])
-       (Correct (Success ([1, 2, 3, 4, 5, 6, 7, 8, 9]))),
+       (Correct ([Success (Result ([1, 2, 3, 4, 5, 6, 7, 8, 9]))])),
 
   Test ('multiline assignment')
        ([Line (70) ('> string')])
        ([Line (71) ('"input may span many lines"')])
-       (Correct (Success ('input may span many lines'))),
+       (Correct ([Success (Result ('input may span many lines'))])),
 
   Test ("spaces following '//' and '>' are optional")
        ([Line (74) ('>"no spaces"')])
        ([Line (75) ('"no spaces"')])
-       (Correct (Success ('no spaces'))),
+       (Correct ([Success (Result ('no spaces'))])),
 
   Test ('indented doctest')
        ([Line (77) ('> "Docco-compatible whitespace"')])
        ([Line (78) ('"Docco-compatible whitespace"')])
-       (Correct (Success ('Docco-compatible whitespace'))),
+       (Correct ([Success (Result ('Docco-compatible whitespace'))])),
 
   Test ("'>' in doctest")
        ([Line (80) ('> 2 > 1')])
        ([Line (81) ('true')])
-       (Correct (Success (true))),
+       (Correct ([Success (Result (true))])),
 
   Test ('comment on input line')
        ([Line (84) ('> "foo" + "bar" // comment')])
        ([Line (85) ('"foobar"')])
-       (Correct (Success ('foobar'))),
+       (Correct ([Success (Result ('foobar'))])),
 
   Test ('comment on output line')
        ([Line (87) ('> 5 * 5')])
        ([Line (88) ('25 // comment')])
-       (Correct (Success (25))),
+       (Correct ([Success (Result (25))])),
 
   Test ('variable in creation context is not accessible')
        ([Line (91) ('> typeof Z')])
        ([Line (92) ('"undefined"')])
-       (Correct (Success ('undefined'))),
+       (Correct ([Success (Result ('undefined'))])),
 
   Test ("'.' should not follow leading '.' in multiline expressions")
        ([Line (95) ('>10 -'),
          Line (96) ('..5')])
        ([Line (97) ('9.5')])
-       (Incorrect (Success (5))
-                  (Success (9.5))),
+       (Incorrect ([Success (Result (5))])
+                  ([Success (Result (9.5))])),
 
   Test ("wrapped lines may begin with more than one '.'")
        ([Line (100) ('> 1000 +'),
@@ -118,12 +118,12 @@ export default ({Test, Line, Incorrect, Correct, Failure, Success}) => [
          Line (103) ('.... 4 +'),
          Line (104) ('..... .5')])
        ([Line (105) ('1234.5')])
-       (Correct (Success (1234.5))),
+       (Correct ([Success (Result (1234.5))])),
 
   Test ('multiline comment')
        ([Line (109) ('> Math.pow(3, 3) - Math.pow(2, 2)')])
        ([Line (110) ('23')])
-       (Correct (Success (23))),
+       (Correct ([Success (Result (23))])),
 
   Test ('multiline comment with wrapped input')
        ([Line (115) ('> ["foo", "bar", "baz"]'),
@@ -131,31 +131,31 @@ export default ({Test, Line, Incorrect, Correct, Failure, Success}) => [
          Line (117) ('. .join(" ")'),
          Line (118) ('. .toUpperCase()')])
        ([Line (119) ('"FOO BAR"')])
-       (Correct (Success ('FOO BAR'))),
+       (Correct ([Success (Result ('FOO BAR'))])),
 
   Test ('multiline comment with leading asterisks')
        ([Line (124) ('> 1 + 2 * 3 * 4')])
        ([Line (125) ('25')])
-       (Correct (Success (25))),
+       (Correct ([Success (Result (25))])),
 
   Test ('multiline comment with leading asterisks')
        ([Line (126) ('> 1 * 2 + 3 + 4 * 5')])
        ([Line (127) ('25')])
-       (Correct (Success (25))),
+       (Correct ([Success (Result (25))])),
 
   Test ('multiline comment with leading asterisks and wrapped input')
        ([Line (132) ('> (function fib(n) {'),
          Line (133) ('.    return n == 0 || n == 1 ? n : fib(n - 2) + fib(n - 1);'),
          Line (134) ('.  })(10)')])
        ([Line (135) ('55')])
-       (Correct (Success (55))),
+       (Correct ([Success (Result (55))])),
 
   Test ('multiline output')
        ([Line (139) ('> ["foo", "bar", "baz"]')])
        ([Line (140) ('[ "foo",'),
          Line (141) ('. "bar",'),
          Line (142) ('. "baz" ]')])
-       (Correct (Success (['foo', 'bar', 'baz']))),
+       (Correct ([Success (Result (['foo', 'bar', 'baz']))])),
 
   Test ('multiline input with multiline output')
        ([Line (145) ('> ["foo", "bar", "baz"]'),
@@ -165,12 +165,12 @@ export default ({Test, Line, Incorrect, Correct, Failure, Success}) => [
        ([Line (149) ('[ "FOO",'),
          Line (150) ('. "BAR",'),
          Line (151) ('. "BAZ" ]')])
-       (Correct (Success (['FOO', 'BAR', 'BAZ']))),
+       (Correct ([Success (Result (['FOO', 'BAR', 'BAZ']))])),
 
   Test ('the rewriter should not rely on automatic semicolon insertion')
        ([Line (154) ('> "the rewriter should not rely"')])
        ([Line (155) ('"on automatic semicolon insertion"')])
-       (Incorrect (Success ('the rewriter should not rely'))
-                  (Success ('on automatic semicolon insertion'))),
+       (Incorrect ([Success (Result ('the rewriter should not rely'))])
+                  ([Success (Result ('on automatic semicolon insertion'))])),
 
 ];
diff --git a/test/statements/results.js b/test/statements/results.js
index 63c55fd..90f8e0a 100644
--- a/test/statements/results.js
+++ b/test/statements/results.js
@@ -1,18 +1,18 @@
-export default ({Test, Line, Correct, Success}) => [
+export default ({Test, Line, Correct, Success, Result}) => [
 
   Test ('var')
        ([Line (3) ('> Math.sqrt(x)')])
        ([Line (4) ('8')])
-       (Correct (Success (8))),
+       (Correct ([Success (Result (8))])),
 
   Test ('let')
        ([Line (8) ('> Math.abs(y)')])
        ([Line (9) ('1')])
-       (Correct (Success (1))),
+       (Correct ([Success (Result (1))])),
 
   Test ('function declaration')
        ([Line (13) ('> fib(10)')])
        ([Line (14) ('55')])
-       (Correct (Success (55))),
+       (Correct ([Success (Result (55))])),
 
 ];
diff --git a/test/transcribe/results.js b/test/transcribe/results.js
index 71e9ac3..4411033 100644
--- a/test/transcribe/results.js
+++ b/test/transcribe/results.js
@@ -1,8 +1,8 @@
-export default ({Test, Line, Correct, Success}) => [
+export default ({Test, Line, Correct, Success, Result}) => [
 
   Test ('accepts Transcribe-style prefix')
        ([Line (11) ('> map(Math.sqrt)([1, 4, 9])')])
        ([Line (12) ('[1, 2, 3]')])
-       (Correct (Success ([1, 2, 3]))),
+       (Correct ([Success (Result ([1, 2, 3]))])),
 
 ];