Added a (when) macro

TODO

@@ -12,8 +12,9 @@ Working TODO list:
 
  - Constructs require for self-hosting
 
-   - named let
    - when
+   - eval
+     there is no concept of macro expansion, probably other deficiencies as well
 
    - vectors
        - make-vector should have an optional 'fill' arg in compiled code

test2.scm

@@ -6,3 +6,7 @@
   (if (zero? i)
     (write 'done)
     (loop (- i 1))))
+
+
+(write (when (lambda () #t) 'true))
+(write (when (lambda () #f) 'false))

transforms.scm

@@ -74,6 +74,12 @@
                 (error "bad let* syntax")))))
     (cons 'begin (lambda (exp rename compare) (begin=>let exp)))
     (cons 'letrec (lambda (exp rename compare) (letrec=>lets+sets exp)))
+    (cons 'when (lambda (exp rename compare)
+      (if (null? (cdr exp)) (error "empty when" exp))
+      (if (null? (cddr exp)) (error "no when body" exp))
+      `(if ,(cadr exp)
+           ((lambda () ,(caddr exp)))
+           #f)))
     (cons 'cond
           (lambda (expr rename compare)
             (if (null? (cdr expr))