shithub: femtolisp

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fixes and improvements to cps converter

--- a/femtolisp/cps.lsp

+++ b/femtolisp/cps.lsp

@@ -16,9 +16,12 @@

                                   ,(progn->cps (cdr forms) k)))))))

 (define (rest->cps xformer form k argsyms)

-  (let ((g (gensym)))

-    (cps- (car form) `(lambda (,g)

-                        ,(xformer (cdr form) k (cons g argsyms))))))

+  (let ((el (car form)))

+    (if (or (atom el) (constantp el))

+        (xformer (cdr form) k (cons el argsyms))

+      (let ((g (gensym)))

+        (cps- el `(lambda (,g)

+                    ,(xformer (cdr form) k (cons g argsyms))))))))

 ; (f x) => (cps- f `(lambda (F) ,(cps- x `(lambda (X) (F ,k X)))))

 (define (app->cps form k argsyms)

@@ -158,10 +161,13 @@

       (any (lambda (p) (contains x p)) form)))

 (define (β-reduce form)

-  (cond ((or (atom form) (constantp form)) form)

+  (if (or (atom form) (constantp form))

+      form

+    (β-reduce- (map β-reduce form))))

+(define (β-reduce- form)

         ; ((lambda (f) (f arg)) X) => (X arg)

-        ((and (= (length form) 2)

+  (cond ((and (= (length form) 2)

               (consp (car form))

               (eq (caar form) 'lambda)

               (let ((args (cadr (car form)))

@@ -172,12 +178,12 @@

                      (eq (car body) (car args))

                      (not (eq (cadr body) (car args)))

                      (symbolp (cadr body)))))

-         `(,(β-reduce (cadr form))

+         `(,(cadr form)

            ,(cadr (caddr (car form)))))

         ; (identity x) => x

         ((eq (car form) *top-k*)

-         (β-reduce (cadr form)))

+         (cadr form))

         ; uncurry:

         ; ((lambda (p1) ((lambda (args...) body) exprs...)) s) =>

@@ -189,7 +195,7 @@

               (or (atom (cadr form)) (constantp (cadr form)))

               (let ((args (cadr (car form)))

                     (s (cadr form))

-                    (body (β-reduce (caddr (car form)))))

+                    (body (caddr (car form))))

                 (and (= (length args) 1)

                      (consp body)

                      (consp (car body))

@@ -203,7 +209,7 @@

                               ,s

                               ,@params)))))))

-        (T (map β-reduce form))))

+        (T form)))

 (defmacro with-delimited-continuations code (cps (f-body code)))

@@ -249,6 +255,8 @@

   cc-lambdas and normal lambdas

 - handle dotted arglists in lambda

+

+- use fewer gensyms

  here's an alternate way to transform a while loop: