altos/scheme: Make for-each tail recursive

Provides a native version of for-each that is tail recursive, rather
than having it just use map and discard the return value.

Signed-off-by: Keith Packard <keithp@keithp.com>

diff --git a/src/scheme/ao_scheme_const.scheme b/src/scheme/ao_scheme_const.scheme
index 4616477f55f9d6218fe36e59dc829cc5d01c51e8..29f000b3c58c976a6513a72a42f3246183c673fe 100644 (file)
--- a/src/scheme/ao_scheme_const.scheme
+++ b/src/scheme/ao_scheme_const.scheme
@@ -512,12 +512,13 @@
 (unless #f (write 'unless))
 
 (define (reverse list)
-  (let ((result ()))
-    (while (not (null? list))
-      (set! result (cons (car list) result))
-      (set! list (cdr list))
-      )
-    result)
+  (define (_r old new)
+    (if (null? old)
+       new
+       (_r (cdr old) (cons (car old) new))
+       )
+    )
+  (_r list ())
   )
 
 (reverse '(1 2 3))
@@ -664,36 +665,46 @@
 
 (define map
   (lambda (proc . lists)
-        (define (args lists)
+        (define (_a lists)
           (cond ((null? lists) ())
                 (else
-                 (cons (caar lists) (args (cdr lists)))
+                 (cons (caar lists) (_a (cdr lists)))
                  )
                 )
           )
-        (define (next lists)
+        (define (_n lists)
           (cond ((null? lists) ())
                 (else
-                 (cons (cdr (car lists)) (next (cdr lists)))
+                 (cons (cdr (car lists)) (_n (cdr lists)))
                  )
                 )
           )
-        (define (domap lists)
+        (define (_m lists)
           (cond ((null? (car lists)) ())
                 (else
-                 (cons (apply proc (args lists)) (domap (next lists)))
+                 (cons (apply proc (_a lists)) (_m (_n lists)))
                  )
                 )
           )
-        (domap lists)
+        (_m lists)
         )
   )
 
 (map cadr '((a b) (d e) (g h)))
 
-(define for-each (lambda (proc . lists)
-                       (apply map proc lists)
-                       #t))
+(define for-each
+  (lambda (proc . lists)
+    (define (_f lists)
+      (cond ((null? (car lists)) #t)
+           (else
+            (apply proc (map car lists))
+            (_f (map cdr lists))
+            )
+           )
+      )
+    (_f lists)
+    )
+  )
 
 (for-each display '("hello" " " "world" "\n"))
 
@@ -708,8 +719,9 @@
 
 (string-map (lambda (x) (+ 1 x)) "HAL")
 
-(define string-for-each (lambda (proc . strings)
-                              (apply for-each proc (_string-ml strings))))
+(define string-for-each
+  (lambda (proc . strings)
+    (apply for-each proc (_string-ml strings))))
 
 (string-for-each write-char "IBM\n")