wip64

2 files changed, 30 insertions, 12 deletions

diff --git a/vikalpa.scm b/vikalpa.scm
index 78b751a..dab81b2 100644
--- a/vikalpa.scm
+++ b/vikalpa.scm
@@ -233,11 +233,7 @@
 
 ;; (expression? x) -> boolean?
 (define (expression? expr)
-  (cond ((expr-quoted? expr)
-         (or (exact-integer? (expr-unquote expr))
-             (boolean? (expr-unquote expr))
-             (symbol? (expr-unquote expr))
-             (null? (expr-unquote expr))))
+  (cond ((expr-quoted? expr) #t)
         ((if-form? expr)
          (and (expression? (if-form-test expr))
               (expression? (if-form-then expr))
@@ -668,6 +664,7 @@
   (and (pair? x)
        (eq? 'error (car x))))
 
+
 (define (rewrite/eval expr sys)
   (let eval ((expr expr))
     (cond
@@ -676,14 +673,29 @@
      ((app-form? expr)
       (let ((args (map eval (app-form-args expr)))
             (name (app-form-name expr)))
+        (define (guard-ok? vars form g)
+          (let ((result (eval (apply-rule '()
+                                          (rule vars '() form g)
+                                          `(,name ,@args)
+                                          '()))))
+            (if (error? result)
+                result
+                (expr-unquote result))))
         (cond
          ((find error? args) => identity)
-         (else
-          (eval (rewrite1 sys
-                          `(,name ,@args)
-                          (lambda args
-                            (cons* 'error 'rewrite name args))
-                          `(rewrite () ,name)))))))
+         ((lookup name sys)
+          => (lambda (f)
+               (let ((gs (get-guards f))
+                     (vars (get-variables f))
+                     (form (defined-function-app-form f)))
+                 (if (every (lambda (g) (guard-ok? vars form g)) gs)
+                     (eval (rewrite1 sys
+                                     `(,name ,@args)
+                                     (lambda args
+                                       (cons* 'error 'rewrite name args))
+                                     `(rewrite () ,name)))
+                     `(error guard-error (,name ,@args) (and ,@gs))))))
+         (else `(error function not-found)))))
      ((if-form? expr)
       (let ((test (eval (if-form-test expr))))
         (if (error? test)
diff --git a/vikalpa/prelude.scm b/vikalpa/prelude.scm
index 201e93d..2da6e8e 100644
--- a/vikalpa/prelude.scm
+++ b/vikalpa/prelude.scm
@@ -161,7 +161,13 @@
   (set-measure-predicate natural?)
   (set-measure-predicate <))
 
-(define-system prelude (prelude/measure/natural)
+(define-system prelude/pair (prelude/measure/natural)
+  (define-core-function pair? (x) pair?)
+  (define-core-function cons (x y) cons)
+  (define-core-function/guard car (x) (pair? x) car)
+  (define-core-function/guard cdr (x) (pair? x) cdr))
+
+(define-system prelude (prelude/pair)
   (define-proof inexact?
     ((rewrite (2) if-nest)
      (rewrite () if-same)))