Experimental support for annotations

hkmc2/shared/src/main/scala/hkmc2/codegen/Lowering.scala

@@ -296,6 +296,10 @@ class Lowering(using TL, Raise, Elaborator.State):
         term(finallyDo)(_ => End()),
         k(Value.Ref(l))
       )
+
+    case Annotated(prefix, receiver) => 
+      // TODO: handle annotations
+      term(receiver)(k)
 
     case Error => End("error")
 

hkmc2/shared/src/main/scala/hkmc2/semantics/BlockImpl.scala

@@ -3,7 +3,7 @@ package semantics
 
 import mlscript.utils.*, shorthands.*
 import syntax.Tree.*
-import hkmc2.syntax.TypeOrTermDef
+import hkmc2.syntax.{Annotations, TypeOrTermDef}
 
 
 trait BlockImpl(using Elaborator.State):
@@ -14,7 +14,7 @@ trait BlockImpl(using Elaborator.State):
   val definedSymbols: Array[Str -> BlockMemberSymbol] =
     desugStmts
       .flatMap:
-        case td: syntax.TypeOrTermDef =>
+        case Annotations(_, td: syntax.TypeOrTermDef) =>
           td.name match
             case L(_) => Nil
             case R(id) =>

hkmc2/shared/src/main/scala/hkmc2/semantics/Elaborator.scala

@@ -429,6 +429,13 @@ extends Importer:
     case Spread(kw, kwLoc, body) =>
       raise(ErrorReport(msg"Illegal position for '${kw.name}' spread operator." -> tree.toLoc :: Nil))
       Term.Error
+    case Annotated(prefix, receiver) => 
+      val ann = prefix match
+      case App(_: Ident | _: SynthSel | _: Sel, _) | _: Ident | _: SynthSel | _: Sel => term(prefix)
+      case _ =>
+        raise(ErrorReport(msg"Unsupported annotation prefix." -> prefix.toLoc :: Nil))
+        Term.Error
+      Term.Annotated(ann, term(receiver))
     // case _ =>
     //   ???
 
@@ -750,6 +757,9 @@ extends Importer:
       case Modified(Keyword.`declare`, absLoc, body) :: sts =>
         // TODO: pass declare to `go`
         go(body :: sts, acc)
+      case Annotated(prefix, receiver) :: sts =>
+        // TODO: pass annotations to `go`
+        go(receiver :: sts, acc)
       case (result: Tree) :: Nil =>
         val res = term(result)
         (Term.Blk(acc.reverse, res), ctx)

hkmc2/shared/src/main/scala/hkmc2/semantics/Term.scala

@@ -39,6 +39,7 @@ enum Term extends Statement:
   case Throw(result: Term)
   case Try(body: Term, finallyDo: Term)
   case Handle(lhs: LocalSymbol, rhs: Term, defs: ObjBody)
+  case Annotated(prefix: Term, receiver: Term)
 
   lazy val symbol: Opt[Symbol] = this match
     case Ref(sym) => S(sym)
@@ -72,6 +73,7 @@ enum Term extends Statement:
     case RegRef(reg, value) => "reference creation"
     case Assgn(lhs, rhs) => "assignment"
     case Deref(ref) => "dereference"
+    case Annotated(prefix, receiver) => "annotation"
 end Term
 
 import Term.*
@@ -126,6 +128,7 @@ sealed trait Statement extends AutoLocated with ProductWithExtraInfo:
     case Try(body, finallyDo) => body :: finallyDo :: Nil
     case Handle(lhs, rhs, defs) => rhs :: defs._1 :: Nil
     case Neg(e) => e :: Nil
+    case Annotated(prefix, receiver) => prefix :: receiver :: Nil
 
   protected def children: Ls[Located] = this match
     case t: Lit => t.lit.asTree :: Nil
@@ -196,6 +199,7 @@ sealed trait Statement extends AutoLocated with ProductWithExtraInfo:
         cls.tparams.map(_.showDbg).mkStringOr(", ", "[", "]")}${
         cls.paramsOpt.fold("")(_.toString)} ${cls.body}"
     case Import(sym, file) => s"import ${sym} from ${file}"
+    case Annotated(prefix, receiver) => s"@${prefix.showDbg} ${receiver.showDbg}"
 
 final case class LetDecl(sym: LocalSymbol) extends Statement
 

hkmc2/shared/src/main/scala/hkmc2/syntax/Parser.scala

@@ -101,6 +101,11 @@ object Parser:
       loc.origin.fph.getLineColAt(loc.spanStart) match
         case (ln, _, col) => s"Ln $ln Col $col"
 
+  extension (trees: Ls[Tree])
+    /** Note that the innermost annotation is the leftmost. */
+    def annotate(tree: Tree): Tree = trees.foldLeft(tree):
+      case (acc, ann) => Annotated(ann, acc)
+
 end Parser
 import Parser._
 
@@ -232,21 +237,24 @@ abstract class Parser(
     maybeIndented((p, i) => p.block(allowNewlines = i))
 
 
-  def block(allowNewlines: Bool)(using Line): Ls[Tree] = blockOf(prefixRules, allowNewlines)
+  def block(allowNewlines: Bool)(using Line): Ls[Tree] = blockOf(prefixRules, Nil, allowNewlines)
 
-  def blockOf(rule: ParseRule[Tree], allowNewlines: Bool)(using Line): Ls[Tree] =
-    wrap(rule.name)(blockOfImpl(rule, allowNewlines))
-  def blockOfImpl(rule: ParseRule[Tree], allowNewlines: Bool): Ls[Tree] =
-    def blockContOf(rule: ParseRule[Tree]): Ls[Tree] =
+  def blockOf(rule: ParseRule[Tree], headAnnotations: Ls[Tree], allowNewlines: Bool)(using Line): Ls[Tree] =
+    wrap(rule.name)(blockOfImpl(rule, headAnnotations, allowNewlines))
+  def blockOfImpl(rule: ParseRule[Tree], headAnnotations: Ls[Tree], allowNewlines: Bool): Ls[Tree] =
+    def blockContOf(rule: ParseRule[Tree], headAnnotations: Ls[Tree] = Nil): Ls[Tree] =
       yeetSpaces match
-        case (COMMA, _) :: _ => consume; blockOf(rule, allowNewlines)
-        case (SEMI, _) :: _ => consume; blockOf(rule, allowNewlines)
-        case (NEWLINE, _) :: _ if allowNewlines => consume; blockOf(rule, allowNewlines)
+        case (COMMA, _) :: _ => consume; blockOf(rule, headAnnotations, allowNewlines)
+        case (SEMI, _) :: _ => consume; blockOf(rule, headAnnotations, allowNewlines)
+        case (NEWLINE, _) :: _ if allowNewlines => consume; blockOf(rule, headAnnotations, allowNewlines)
         case _ => Nil
     cur match
     case Nil => Nil
-    case (NEWLINE, _) :: _ if allowNewlines => consume; blockOf(rule, allowNewlines)
-    case (SPACE, _) :: _ => consume; blockOf(rule, allowNewlines)
+    case (NEWLINE, _) :: _ if allowNewlines => consume; blockOf(rule, headAnnotations, allowNewlines)
+    case (SPACE, _) :: _ => consume; blockOf(rule, headAnnotations, allowNewlines)
+    case (IDENT("@", _), l0) :: _ =>
+      consume
+      blockOf(rule, simpleExpr(AppPrec) :: headAnnotations, allowNewlines)
     case (tok @ (id: IDENT), loc) :: _ =>
       Keyword.all.get(id.name) match
       case S(kw) =>
@@ -256,14 +264,14 @@ abstract class Parser(
           yeetSpaces match
           case (tok @ BRACKETS(Indent | Curly, toks), loc) :: _ if subRule.blkAlt.isEmpty =>
             consume
-            val blk = rec(toks, S(tok.innerLoc), tok.describe).concludeWith(_.blockOf(subRule, allowNewlines)) // FIXME allowNewlines?
+            val blk = rec(toks, S(tok.innerLoc), tok.describe).concludeWith(_.blockOf(subRule, Nil, allowNewlines)) // FIXME allowNewlines?
             if blk.isEmpty then
               err((msg"Expected ${subRule.whatComesAfter} ${subRule.mkAfterStr}; found end of block instead" -> S(loc) :: Nil))
               errExpr
-            blk ::: blockContOf(rule)
+            blk ::: blockContOf(rule) // TODO: apply headAnnotations
           case _ =>
             val res = parseRule(CommaPrecNext, subRule).getOrElse(errExpr)
-            exprCont(res, CommaPrecNext, false) :: blockContOf(rule)
+            headAnnotations.annotate(exprCont(res, CommaPrecNext, false)) :: blockContOf(rule)
         case N =>
 
           // TODO dedup this common-looking logic:
@@ -273,26 +281,29 @@ abstract class Parser(
             yeetSpaces match
             case (tok @ BRACKETS(Indent | Curly, toks), loc) :: _ /* if subRule.blkAlt.isEmpty */ =>
               consume
+              headAnnotations match
+              case Nil => ()
+              case head :: _ =>
+                err((msg"Blocks are not allowed after annotations" -> head.toLoc :: Nil))
               prefixRules.kwAlts.get(kw.name) match
               case S(subRule) if subRule.blkAlt.isEmpty =>
                 rec(toks, S(tok.innerLoc), tok.describe).concludeWith { p =>
-                  p.blockOf(subRule.map(e => parseRule(CommaPrecNext, exprAlt.rest).map(res => exprAlt.k(e, res)).getOrElse(errExpr)), allowNewlines)
+                  p.blockOf(subRule.map(e => parseRule(CommaPrecNext, exprAlt.rest).map(res => exprAlt.k(e, res)).getOrElse(errExpr)), Nil, allowNewlines)
                 } ++ blockContOf(rule)
               case _ =>
                 TODO(cur)
             case _ =>
               prefixRules.kwAlts.get(kw.name) match
               case S(subRule) =>
                 val e = parseRule(CommaPrecNext, subRule).getOrElse(errExpr)
-                parseRule(CommaPrecNext, exprAlt.rest).map(res => exprAlt.k(e, res)).getOrElse(errExpr) :: blockContOf(rule)
+                headAnnotations.annotate(parseRule(CommaPrecNext, exprAlt.rest).map(res => exprAlt.k(e, res)).getOrElse(errExpr)) :: blockContOf(rule)
               case N =>
                 // TODO dedup?
                 err((msg"Expected ${rule.whatComesAfter} ${rule.mkAfterStr}; found ${tok.describe} instead" -> S(loc) :: Nil))
-                errExpr :: blockContOf(rule)
+                headAnnotations.annotate(errExpr) :: blockContOf(rule)
           case N =>
             err((msg"Expected ${rule.whatComesAfter} ${rule.mkAfterStr}; found ${tok.describe} instead" -> S(loc) :: Nil))
-            errExpr :: blockContOf(rule)
-
+            headAnnotations.annotate(errExpr) :: blockContOf(rule)
       case N =>
         val lhs = tryParseExp(CommaPrecNext, tok, loc, rule).getOrElse(errExpr)
         cur match
@@ -301,9 +312,9 @@ abstract class Parser(
           val rhs = expr(CommaPrecNext)
           Def(lhs, rhs) :: blockContOf(rule)
         case _ =>
-          lhs :: blockContOf(rule)
+          headAnnotations.annotate(lhs) :: blockContOf(rule)
     case (tok, loc) :: _ =>
-      tryParseExp(CommaPrecNext, tok, loc, rule).getOrElse(errExpr) :: blockContOf(rule)
+      headAnnotations.annotate(tryParseExp(CommaPrecNext, tok, loc, rule).getOrElse(errExpr)) :: blockContOf(rule)
 
 
   private def tryParseExp[A](prec: Int, tok: Token, loc: Loc, rule: ParseRule[A]): Opt[A] =
@@ -467,6 +478,10 @@ abstract class Parser(
   def simpleExpr(prec: Int)(using Line): Tree = wrap(prec)(simpleExprImpl(prec))
   def simpleExprImpl(prec: Int): Tree =
     yeetSpaces match
+    case (IDENT("@", _), l0) :: _ =>
+      consume
+      val ann = simpleExpr(AppPrec)
+      Annotated(ann, simpleExpr(prec))
     case (IDENT(nme, sym), loc) :: _ =>
       Keyword.all.get(nme) match
         case S(kw) => // * Expressions starting with keywords should be handled in parseRule

hkmc2/shared/src/main/scala/hkmc2/syntax/Tree.scala

@@ -74,6 +74,7 @@ enum Tree extends AutoLocated:
   case RegRef(reg: Tree, value: Tree)
   case Effectful(eff: Tree, body: Tree)
   case Spread(kw: Keyword.Ellipsis, kwLoc: Opt[Loc], body: Opt[Tree])
+  case Annotated(prefix: Tree, receiver: Tree)
 
   def children: Ls[Tree] = this match
     case _: Empty | _: Error | _: Ident | _: Literal => Nil
@@ -107,6 +108,7 @@ enum Tree extends AutoLocated:
     case Open(bod) => bod :: Nil
     case Def(lhs, rhs) => lhs :: rhs :: Nil
     case Spread(_, _, body) => body.toList
+    case Annotated(prefix, receiver) => prefix :: receiver :: Nil
 
   def describe: Str = this match
     case Empty() => "empty"
@@ -142,6 +144,7 @@ enum Tree extends AutoLocated:
     case Handle(_, _, _, _) => "handle"
     case Def(lhs, rhs) => "defining assignment"
     case Spread(_, _, _) => "spread"
+    case Annotated(prefix, receiver) => "annotated"
 
   def showDbg: Str = toString // TODO
 
@@ -191,6 +194,11 @@ object Apps:
   def unapply(t: Tree): S[(Tree, Ls[Tup])] = t match
     case App(Apps(id, args), arg: Tup) => S(id, args :+ arg)
     case t => S(t, Nil)
+
+object Annotations:
+  def unapply(t: Tree): Opt[(Ls[Tree], Tree)] = t match
+    case Annotated(p, Annotations(ps, recv)) => S(p :: ps, recv)
+    case other => S((Nil, other))
 
 
 sealed abstract class OuterKind(val desc: Str)

hkmc2/shared/src/test/mlscript/syntax/Annotations.mls

@@ -0,0 +1,71 @@
+:js
+
+module tailrec
+
+tailrec
+//│ = tailrec { class: [class tailrec] }
+
+@tailrec fun fact_n(n, acc) =
+  if n == 0 then acc else fact(n - 1, n * acc)
+
+fun fact(n) =
+  @tailrec fun go(n, acc) =
+    if n == 0 then acc else go(n - 1, n * acc)
+  go(n, 1)
+
+module compile
+
+class SomePattern
+
+:e // TODO: pattern compilation
+fun foo(x) = if x is @compile SomePattern then "yes" else "no"
+//│ ╔══[ERROR] Unrecognized pattern.
+//│ ║  l.21: 	fun foo(x) = if x is @compile SomePattern then "yes" else "no"
+//│ ╙──      	                      ^^^^^^^^^^^^^^^^^^^
+
+module debug
+
+@debug 0
+//│ = 0
+
+@debug 1 + 2
+//│ = 3
+
+(@debug 1 + 2)
+//│ = 3
+
+(@debug 1) + 2
+//│ = 3
+
+(1 + @debug 2)
+//│ = 3
+
+class Log(msg: Str)
+
+fact(@Log 5)
+//│ = 120
+
+class Freezed(degree: Num)
+
+@Freezed(-273.15) class AbsoluteZero
+
+@Freezed(-18) class Beverage(name: Str)
+
+@Freezed(-4) let drink = Beverage("Coke")
+//│ drink = Beverage { name: 'Coke' }
+
+module Foo with
+  class Bar(qax: Str)
+
+@Foo.Bar("baz") class Qux
+
+@42 class Qux
+
+:pe
+@1 + 2 class Qux
+//│ ╔══[PARSE ERROR] Expected end of input; found 'class' keyword instead
+//│ ║  l.65: 	@1 + 2 class Qux
+//│ ╙──      	       ^^^^^
+//│ = 2
+
+@(1 + 2) class Qux