fix else as only expression in cond #366

CHANGELOG.md

@@ -18,6 +18,7 @@
 * fix processing list with nested unquote-splicing [#362](https://github.com/LIPS-scheme/lips/issues/362)
 * fix exception during error from eval [#362](https://github.com/LIPS-scheme/lips/issues/362)
 * allow to catch exceptions from eval
+* fix else keyword as only expression in cond [#366](https://github.com/LIPS-scheme/lips/issues/366)
 
 ## 1.0.0-beta.19
 ### Breaking

README.md

@@ -7,7 +7,7 @@
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+[![Coverage Status](https://coveralls.io/repos/github/jcubic/lips/badge.svg?branch=devel&6046de8d07eaf73d7b32a46f0fb3d24f)](https://coveralls.io/github/jcubic/lips?branch=devel)
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lib/bootstrap.scm

@@ -552,13 +552,25 @@
 
    Helper macro used by cond.")
 
+;; -----------------------------------------------------------------------------
+(define (%else-literal? obj)
+  "(%else-literal? obj)
+
+   Checks if object is symbol else."
+  (and (symbol? obj)
+       (or (eq? obj 'else)
+           (eq? (--> (new lips.LString (obj.literal))
+                     (cmp "else")) 0))))
+
 ;; -----------------------------------------------------------------------------
 (define-macro (cond . list)
   "(cond (predicate? . body)
-         (predicate? . body))
+         (predicate? . body)
+         (else . body))
 
    (cond (predicate? => procedure)
-         (predicate? => procedure))
+         (predicate? => procedure)
+         (else . body))
 
    Macro for condition checks. For usage instead of nested ifs.
    You can use predicate and any number of expressions. Or symbol =>
@@ -573,21 +585,16 @@
                              (caddr item)
                              (cdr item)))
              (rest (cdr list)))
-        `(let ((,value ,first))
-           (if ,value
-               ,(if fn
-                    `(,expression ,value)
-                    `(begin
-                       ,@expression))
-               ,(if (and (pair? rest)
-                         (let ((x (caar rest)))
-                           (or (eq? x true)
-                               (and (symbol? x)
-                                    (or (eq? x 'else)
-                                        (eq? (--> (new lips.LString (x.literal)) (cmp "else")) 0))))))
-                    `(begin
-                       ,@(cdar rest))
-                    (if (not (null? rest))
+        (if (%else-literal? first)
+            `(begin
+               ,@expression)
+            `(let ((,value ,first))
+               (if ,value
+                   ,(if fn
+                        `(,expression ,value)
+                        `(begin
+                           ,@expression))
+                   ,(if (not (null? rest))
                         `(cond ,@rest))))))
       '()))
 

tests/std.scm

@@ -351,3 +351,11 @@
                          x
                     x"))))
 
+(test "std: cond"
+      (lambda (t)
+        (t.is (cond (else 10)) 10)
+        (t.is (cond ((zero? 0) 10) (else 20)) 10)
+        (t.is (cond ((zero? 10) 10) (else 20)) 20)
+        (t.is (let ((alist '((a . 10) (b . 20) (c . 30))))
+                (cond ((assoc 'b alist) => cdr) (else #f)))
+              20)))