Add let bindings

[scheme.git] / compiler.scm

diff --git a/compiler.scm b/compiler.scm
index 351e11b7695f927121d574baef27924ed2d31f67..d79a37a26f77babdd28040991efa8003ca25ecc1 100644 (file)
--- a/compiler.scm
+++ b/compiler.scm
@@ -1,11 +1,12 @@
 (load "typecheck.scm")
+(load "ast.scm")
 
 (define (emit . s)
   (begin
     (apply printf s)
     (display "\n")))
 
-(define (compile-add xs)
+(define (codegen-add xs)
   (define (go ys)
     (if (null? ys)
       (emit "movq %rbx, %rax")
@@ -16,12 +17,42 @@
     (emit "movq $0, %rbx")
     (go xs)))
 
-(define (compile-expr e)
-  (if (and (list? e) (eq? (car e) '+))
-      (compile-add (cdr e))
-      (emit "movq $~a, %rax" e)))
+(define (range s n)
+  (if (= 0 n) '()
+      (append (range s (- n 1))
+             (list (+ s (- n 1))))))
 
-(define (compile-program program)
+(define wordsize 8)
+
+(define (codegen-let bindings body si env)
+  (let* ((stack-offsets (map (lambda (x) (- si (* x wordsize)))
+                            (range 0 (length bindings))))
+        (inner-si (- si (* (length bindings) wordsize)))
+        (names (map car bindings))
+        (exprs (map cadr bindings))
+        (inner-env (append (map cons names stack-offsets) env)))
+  (for-each (lambda (expr offset)
+             (codegen-expr expr inner-si env)
+             (emit "movq %rax, ~a(%rsp)" offset))
+           exprs stack-offsets)
+  (for-each (lambda (form) (codegen-expr form inner-si inner-env)) body)))
+
+(define (codegen-var name si env)
+  (let ((offset (cdr (assoc name env))))
+    (emit "movq ~a(%rsp), %rax" offset)))
+
+(define (codegen-expr e si env)
+  (cond ((and (list? e) (eq? (car e) '+))
+        (codegen-add (cdr e)))
+       ((let? e) (codegen-let
+                  (let-bindings e)
+                  (let-body e)
+                  si
+                  env))
+       ((var? e) (codegen-var e si env))
+       (else (emit "movq $~a, %rax" e))))
+
+(define (codegen program)
   (emit ".text")
   (emit ".p2align 4,,15")
   (emit ".globl _scheme_entry")
@@ -37,7 +68,7 @@
            '(12 13 14 15))
 
   ; our code goes here
-  (compile-expr program)
+  (codegen-expr program 0 '())
 
   ; restore preserved registers
   (for-each (lambda (i)
@@ -55,5 +86,5 @@
   (let ([tmp-path "/tmp/a.s"])
     (when (file-exists? tmp-path) (delete-file tmp-path))
     (with-output-to-file tmp-path
-      (lambda () (compile-program program)))
+      (lambda () (codegen program)))
     (system "clang -fomit-frame-pointer /tmp/a.s rts.c")))