X-Git-Url: https://thelambdalab.xyz/gitweb/index.cgi?a=blobdiff_plain;f=scheme-library.scm;h=5ee0b49c2c7e88b4bfb4a922df27b4dd52e70a03;hb=55761030cc43072bbc8b2d1ef5a053fc64a6a3ec;hp=b92795dfd03f29005d13aa3ac9eb57e5abadbfb3;hpb=050cc9a7e651ba8eacb054283307f4d06141c302;p=scheme.forth.jl.git

diff --git a/scheme-library.scm b/scheme-library.scm
index b92795d..5ee0b49 100644
--- a/scheme-library.scm
+++ b/scheme-library.scm
@@ -7,6 +7,12 @@
 (define (null? args)
   (eq? args ()))
 
+(define (caar l) (car (car l)))
+(define (cadr l) (car (cdr l)))
+(define (cdar l) (cdr (car l)))
+(define (cddr l) (cdr (cdr l)))
+(define (cadar l) (car (cdr (car l))))
+
 ; Join two lists together
 (define (join l1 l2)
   (if (null? l1)
@@ -29,11 +35,45 @@
 
 ;; LIBRARY FORMS
 
+
+; let
+
+(define (let-vars args)
+  (if (null? args)
+    '()
+    (cons (caar args) (let-vars (cdr args)))))
+
+(define (let-inits args)
+  (if (null? args)
+    '()
+  (cons (cadar args) (let-inits (cdr args)))))
+
+(define-macro (let args . body)
+              `((lambda ,(let-vars args)
+                 ,@body) ,@(let-inits args)))
+
+; while
+
+(define-macro (while condition . body)
+              (define loop (gensym))
+              `(begin
+                 (define (,loop)
+                   (if ,condition
+                     (begin ,@body (,loop))))
+                 (,loop)))
+
 ;; TESTING
 
 (define-macro (backwards . body)
               (cons 'begin (reverse body)))
 
+; Test for the while macro.
+(define (count)
+  (define counter 10)
+  (while (> counter 0)
+         (display counter) (newline)
+         (set! counter (- counter 1))))
+
 ; Basic iterative summation.  Run this on large numbers to
 ; test garbage collection and tail-call optimization.
 (define (sum n)