From 844dcd052c6f551d9936693c2b4c49cf920c7051 Mon Sep 17 00:00:00 2001
From: Luke Lau <luke_lau@icloud.com>
Date: Sun, 4 Aug 2019 21:22:57 +0100
Subject: [PATCH] Formulate destructors properly

---
 ast.scm       | 44 +++++++++++++++++++++++++++++++++++++++++++-
 tests.scm     |  9 +++++++++
 typecheck.scm | 41 +++++++++++++++++------------------------
 3 files changed, 69 insertions(+), 25 deletions(-)

diff --git a/ast.scm b/ast.scm
index 3b4d164..5064ca5 100644
--- a/ast.scm
+++ b/ast.scm
@@ -75,7 +75,7 @@
     (if (eqv? (ast-type x) 'var)
 	(list (cons x body))
 	(let* ([constructor (car x)]
-	      [destructor (lambda (i) `(destruct ,i ,constructor))])
+	       [destructor (lambda (i) (dtor-name constructor i))])
 	  (flat-map (lambda (y i)
 		      (pattern-match y (list (destructor i) body)))
 		    (cdr x)
@@ -108,6 +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
diff --git a/tests.scm b/tests.scm
index 3987930..30d23f6 100644
--- a/tests.scm
+++ b/tests.scm
@@ -43,6 +43,15 @@
   (let ((str (read-file "/tmp/test-output.txt")))
     (test str output)))
 
+(test (data-tors '(data A
+			(foo Int Bool)
+			(bar Bool)))
+      '((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))))
+
 (test-types (typecheck '((lambda (x) (+ ((lambda (y) (x y 3)) 5) 2))))
 	    '(abs (abs Int (abs Int Int)) Int))
 
diff --git a/typecheck.scm b/typecheck.scm
index 4cc9349..8210352 100644
--- a/typecheck.scm
+++ b/typecheck.scm
@@ -37,7 +37,7 @@
 
 					; ('a, ('b, 'a))
 (define (env-lookup env n)
-  (if (null? env) (error #f "empty env")			; it's a type equality
+  (if (null? env) (error #f "empty env" env n)			; it's a type equality
       (if (eq? (caar env) n)
 	  (cdar env)
 	  (env-lookup (cdr env) n))))
@@ -136,11 +136,11 @@
     (check new-env (last (let-body x)))))
 
 (define (check env x)
-  (display "check: ")
-  (display x)
-  (display "\n\t")
-  (display env)
-  (newline)
+  ;; (display "check: ")
+  ;; (display x)
+  ;; (display "\n\t")
+  ;; (display env)
+  ;; (newline)
   (let
       ((res
 	(case (ast-type x)
@@ -227,31 +227,24 @@
 		     (let ((return-type (substitute cs (caddr resolved-func-type))))
 		       (list cs return-type))
 		     (error #f "not a function")))))))
-    (display "result of ")
-    (display x)
-    (display ":\n\t")
-    (display (pretty-type (cadr res)))
-    (display "\n\t[")
-    (display (pretty-constraints (car res)))
-    (display "]\n")
+    ;; (display "result of ")
+    ;; (display x)
+    ;; (display ":\n\t")
+    ;; (display (pretty-type (cadr res)))
+    ;; (display "\n\t[")
+    ;; (display (pretty-constraints (car res)))
+    ;; (display "]\n")
     res))
 
 					; we typecheck the lambda calculus only (only single arg lambdas)
 (define (typecheck prog)
-  (define (constructor-type t ctr)
-    (fold-left (lambda (acc x) `(abs ,x ,acc)) t (cdr ctr)))
-  (define (constructors data-def)
-    (let ([type-name (cadr data-def)]
-	  [ctrs (cddr data-def)])
-    (fold-left (lambda (acc ctr)
-		 (cons (cons (car ctr) (constructor-type type-name ctr))
-		       acc))
-	       '()
-	       ctrs)))
-  (let ([init-env (flat-map constructors (program-datas prog))])
+
+  (let ([init-env (flat-map data-tors (program-datas prog))])
     (display init-env)
+    (newline)
     (cadr (check init-env (normalize (program-body prog))))))
 
+  
 					; returns a list of constraints
 (define (~ a b)
   (let ([res (unify? a b)])
-- 
2.30.2