Formulate destructors properly

[scheme.git] / ast.scm

diff --git a/ast.scm b/ast.scm
index 469a96f7162cb09c77dac0ed71b971dcbbd179a0..5064ca554bc8033bdbc0b483ac79249cd3312f73 100644 (file)
--- a/ast.scm
+++ b/ast.scm
@@ -71,8 +71,16 @@
     [else (p x)]))
 
 (define (let-bindings e)
-  (define (extract x)  ) ; TODO
-  (flat-map extract (cadr e))
+  (define (pattern-match x body)
+    (if (eqv? (ast-type x) 'var)
+       (list (cons x body))
+       (let* ([constructor (car x)]
+              [destructor (lambda (i) (dtor-name constructor i))])
+         (flat-map (lambda (y i)
+                     (pattern-match y (list (destructor i) body)))
+                   (cdr x)
+                   (range 0 (length (cdr x)))))))
+  (flat-map (lambda (x) (pattern-match (car x) (cdr x))) (cadr e)))
 (define let-body cddr)
 
 (define (lambda? x)
@@ -100,6 +108,48 @@
      ,@(filter (lambda (x) (eqv? (statement-type x) 'expr))
               program)))
 
+                                       ; gets both constructors and destructors
+                                       ; (data A (foo Int Bool)
+                                       ;         (bar Bool))
+                                       ;        |
+                                       ;        v
+                                       ; (foo . (abs Int (abs Bool A)))
+                                       ; (foo~0 . (abs A Int)
+                                       ; (foo~1 . (abs A Bool)
+                                       ; (bar . (abs Bool A)
+                                       ; (bar~0 . (abs A Bool)
+
+(define (data-tors data-def)
+  (define (constructor-type t products)
+    (fold-right (lambda (x acc) `(abs ,x ,acc)) t products))
+
+  (define (destructor ctor-name prod-type part-type index)
+    (let ([name (dtor-name ctor-name index)])
+      (cons name `(abs ,prod-type ,part-type))))
+  
+  (let ([type-name (cadr data-def)]
+        [ctors (cddr data-def)])
+    (fold-right
+     (lambda (ctor acc)       
+       (let* ([ctor-name (car ctor)]
+             [products (cdr ctor)]
+             
+             [maker (cons ctor-name (constructor-type type-name products))]
+             
+             [dtors (map (lambda (t i) (destructor ctor-name type-name t i))
+                         products
+                         (range 0 (length products)))])
+        
+        (cons maker (append dtors acc))))
+     '()
+     ctrs)))
+
+(define (dtor-name ctor-name index)
+  (string->symbol
+   (string-append (symbol->string ctor-name)
+                 "~"
+                 (number->string index))))
+
 ; for use in normalized form
 (define lambda-arg caadr)
 ; for use elsewhere
@@ -107,7 +157,12 @@
 (define lambda-body caddr)
 
                                        ; utils
-(define (flat-map f x) (fold-left append '() (map f x)))
+(define (range s n)
+  (if (= 0 n) '()
+      (append (range s (- n 1))
+             (list (+ s (- n 1))))))
+
+(define (flat-map f . xs) (fold-left append '() (apply map (cons f xs))))
 (define (repeat x n) (if (<= n 0) '()
                         (cons x (repeat x (- n 1)))))