From 25a4c23da2d76f3bb951d01b1c3175be80441a0a Mon Sep 17 00:00:00 2001
From: Luke Lau <luke_lau@icloud.com>
Date: Tue, 23 Jul 2019 01:36:06 +0100
Subject: [PATCH] Codegen if statements

---
 codegen.scm   | 35 ++++++++++++++++++++++++++++++++---
 tests.scm     |  2 +-
 typecheck.scm |  8 +-------
 3 files changed, 34 insertions(+), 11 deletions(-)

diff --git a/codegen.scm b/codegen.scm
index 70a8ca4..a19b53d 100644
--- a/codegen.scm
+++ b/codegen.scm
@@ -38,6 +38,14 @@
   (emit "notq %rax")
   (emit "andq $1, %rax"))
 
+(define (codegen-eq a b si env)
+  (codegen-expr a si env)
+  (emit "movq %rax, ~a(%rsp)" si)
+  (codegen-expr b (- si wordsize) env)
+  (emit "subq ~a(%rsp), %rax" si)
+  (emit "not %rax")
+  (emit "andq $1, %rax"))
+
 (define (range s n)
   (if (= 0 n) '()
       (append (range s (- n 1))
@@ -76,6 +84,8 @@
 
 					; for now we can only call closures
 (define (codegen-call closure args si env)
+  (when (not (eq? (ast-type closure) 'closure))
+    (error #f (format "~a is not a closure" closure)))
   (let* ((captured (caddr closure))
 	 (label (cadr closure))
 	 (argument-start (length captured)))
@@ -135,6 +145,23 @@
        (codegen-expr body (* (- wordsize) (length vars)) env)
        ))))			; move args and capture vars to stack
 
+(define cur-label 0)
+(define (fresh-label)
+  (set! cur-label (+ 1 cur-label))
+  (format "label~a" (- cur-label 1)))
+
+(define (codegen-if cond then else si env)
+  (codegen-expr cond si env)
+  (emit "cmpq $0, %rax")
+  (let ((exit-label (fresh-label))
+	(else-label (fresh-label)))
+    (emit "je ~a" else-label)
+    (codegen-expr then si env)
+    (emit "jmp ~a" exit-label)
+    (emit "~a:" else-label)
+    (codegen-expr else si env)
+    (emit "~a:" exit-label)))
+
 (define (codegen-expr e si env)
   (case (ast-type e)
     ('builtin e)
@@ -146,6 +173,7 @@
 	 ('- (codegen-sub (cadr e) (caddr e) si env))
 	 ('* (codegen-mul (cadr e) (caddr e) si env))
 	 ('! (codegen-not (cadr e) si env))
+	 ('= (codegen-eq  (cadr e) (caddr e) si env))
 	 ('bool->int (codegen-expr (cadr e) si env))
 	 (else (codegen-call callee (cdr e) si env)))))
 
@@ -156,6 +184,8 @@
 
     ('var (codegen-var e si env))
 
+    ('if (codegen-if (cadr e) (caddr e) (cadddr e) si env))
+
     ('string-literal (emit "movq ~a, %rax" label))
     ('bool-literal (emit "movq $~a, %rax" (if e 1 0)))
     ('int-literal (emit "movq $~a, %rax" e))
@@ -200,12 +230,11 @@
   (define (extract e)
     (case (ast-type e)
       ('lambda (add-lambda e))
-     ('let `(let
-		    ,(map extract (let-bindings e))
+      ('let `(let ,(map extract (let-bindings e))
 	       ,@(map extract (let-body e))))
       ('app (append (list (extract (car e)))
 		    (map extract (cdr e))))
-     (else e)))
+      (else (ast-traverse extract e))))
   (let ((transformed (extract program)))
     (cons lambdas transformed)))
 
diff --git a/tests.scm b/tests.scm
index 964b644..56762c7 100644
--- a/tests.scm
+++ b/tests.scm
@@ -28,9 +28,9 @@
 
 (test-prog '(+ 1 2) "3")
 (test-prog '((lambda (x) ((lambda (y) (+ x y)) 42)) 100) "142")
-; todo: support recursive let
 (test-prog '(let ((x (+ 1 32))
 		  (y x))
 	      ((lambda (z) (+ 1 z)) (* y x)))
 	   "1090")
+(test-prog '(if ((lambda (x) (= x 2)) 1) 0 (- 32 1)) "31")
 
diff --git a/typecheck.scm b/typecheck.scm
index 197798e..46fddfe 100644
--- a/typecheck.scm
+++ b/typecheck.scm
@@ -46,7 +46,6 @@
       (car xs)
       (last (cdr xs))))
 				
-					
 (define (normalize prog) ; (+ a b) -> ((+ a) b)
   (case (ast-type prog)
     ('lambda 
@@ -60,17 +59,12 @@
 	 `(,(normalize (car prog)) ,(normalize (cadr prog))) ; (f a)
 	 `(,(list (normalize (car prog)) (normalize (cadr prog)))
 	   ,(normalize (caddr prog))))) ; (f a b)
-    ;; (list (list (normalize (car prog))
-    ;; 	    (normalize (cadr prog))) (normalize (caddr prog))))) ; (f a b)
     ('let
 	(append (list 'let
 		      (map (lambda (x) `(,(car x) ,(normalize (cadr x))))
 			   (let-bindings prog)))
 		(map normalize (let-body prog))))
-    ('if `(if ,(normalize (cadr prog))
-	      ,(normalize (caddr prog))
-	      ,(normalize (cadddr prog))))
-    (else prog)))
+    (else (ast-traverse normalize prog))))
 
 (define (builtin-type x)
   (case x
-- 
2.30.2