From c4a5f8ab1efce20f0e1181ffe34639facb19594a Mon Sep 17 00:00:00 2001
From: Luke Lau <luke_lau@icloud.com>
Date: Mon, 12 Aug 2019 16:26:21 +0100
Subject: [PATCH] Move expanding pattern matches to its own transformations

I think this will make it easier to understand how pattern matching
works
---
 ast.scm       | 41 ++++++++++++++++++++++++++++++-----------
 codegen.scm   |  5 ++++-
 tests.scm     | 14 ++++++--------
 typecheck.scm |  8 ++++++--
 4 files changed, 46 insertions(+), 22 deletions(-)

diff --git a/ast.scm b/ast.scm
index 9af3653..8a98617 100644
--- a/ast.scm
+++ b/ast.scm
@@ -75,19 +75,31 @@
     ['stack (either (p x) (inner (caddr x)))]
     [else (p x)]))
 
-(define (let-bindings e)
-  (define (pattern-match binding body)
-    (if (eqv? (ast-type binding) 'var)
-	(list (cons binding body))
-	(let* ([constructor (car binding)]
-	       [destructor (lambda (i) (dtor-name constructor i))])
-	  (flat-map (lambda (y i)
-		      (pattern-match y `((,(destructor i) ,@body))))
-		    (cdr binding)
-		    (range 0 (length (cdr binding)))))))
-  (flat-map (lambda (x) (pattern-match (car x) (cdr x))) (cadr e)))
+(define let-bindings cadr)
 (define let-body cddr)
 
+					; (let ([(foo a b) (foo 123 345)]) a)
+					;   |
+					;   v
+					; (let ([a (foo~0 (foo 123 345)]
+                                        ;       [b (foo~1 (foo 123 345)]) a)
+(define (expand-pattern-matches x)  
+  (define (pattern-match binding)
+    (let ([binding-name (car binding)]
+	  [body (cadr binding)])
+      (if (eqv? (ast-type binding-name) 'var)
+	  (list (list binding-name body))
+	  (let* ([sum-name (car binding-name)]
+		 [destructor (lambda (i) (dtor-name sum-name i))])
+	    (flat-map (lambda (y i)
+			(pattern-match (list y `(,(destructor i) ,body))))
+		      (cdr binding-name)
+		      (range 0 (length (cdr binding-name))))))))
+  (case (ast-type x)
+      ['let `(let ,(flat-map pattern-match (let-bindings x))
+	          ,@(map expand-pattern-matches (let-body x)))]
+      [else (ast-traverse expand-pattern-matches x)]))
+
 (define (lambda? x)
   (and (list? x) (eq? (car x) 'lambda)))
 
@@ -112,6 +124,13 @@
   (filter (lambda (x) (eqv? (statement-type x) 'defines))
 	  program))
 
+(define (program-map-exprs f program)
+  (map (lambda (x)
+	 (case (statement-type x)
+	   ['expr (f x)]
+	   [else x]))
+       program))
+
 (define (program-body program)
   ; hack to have multi-expression bodies
   `(let ()
diff --git a/codegen.scm b/codegen.scm
index 7a37097..8e3a7d5 100644
--- a/codegen.scm
+++ b/codegen.scm
@@ -658,7 +658,10 @@
   (set! cur-lambda 0)
   (let* ([data-layouts (program-data-layouts program)]
 
-	 [type-annotated (annotate-types program)]
+	 [pattern-matched (program-map-exprs
+			   expand-pattern-matches
+			   program)]
+	 [type-annotated (annotate-types pattern-matched)]
 	 [stack-annotated (annotate-stack-values data-layouts
 						 type-annotated)]
 	 
diff --git a/tests.scm b/tests.scm
index 2b6e09a..bcd878a 100644
--- a/tests.scm
+++ b/tests.scm
@@ -61,6 +61,12 @@
 	(bar . (abs Bool A))
 	(bar~0 . (abs A Bool))))
 
+(test (expand-pattern-matches '(let ([(foo x y) (foo 123 234)] [z (f 123)]) x))
+      '(let ([x (foo~0 (foo 123 234))]
+	     [y (foo~1 (foo 123 234))]
+	     [z (f 123)])
+	 x))
+
 (test-types (typecheck '((lambda (x) (+ ((lambda (y) (x y 3)) 5) 2))))
 	    '(abs (abs Int (abs Int Int)) Int))
 
@@ -137,14 +143,6 @@
  'Int)
 
 
-					; pattern matching
-(test (let-bindings '(let ([(foo x) a]) x))
-      '((x (foo~0 a))))
-
-(test (let-bindings '(let ([x (foo 42)] [(foo y) x]) x))
-      '((x (foo 42))
-	(y (foo~0 x))))
-
 					; type annotations
 
 (test (annotate-types
diff --git a/typecheck.scm b/typecheck.scm
index 35e8188..a526620 100644
--- a/typecheck.scm
+++ b/typecheck.scm
@@ -259,7 +259,8 @@
 
 					; we typecheck the lambda calculus only (only single arg lambdas)
 (define (typecheck prog)
-  (cadr (check (init-adts-env prog) (normalize (program-body prog)))))
+  (let ([expanded (program-map-exprs expand-pattern-matches prog)])
+    (cadr (check (init-adts-env expanded) (normalize (program-body expanded))))))
 
 
 					; before passing annotated types onto codegen
@@ -309,8 +310,11 @@
 
 (define ann-expr car)
 (define ann-type caddr)
+
+					; prerequisites: expand-pattern-matches
 (define (annotate-types prog)
-  (denormalize (program-body prog)
+  (denormalize
+   (program-body prog)
    (caddr (check (init-adts-env prog)(normalize (program-body prog))))))
 
   
-- 
2.30.2