Implement the zero? predicate

scm/inc/compiler.scm

@@ -45,7 +45,15 @@
        (emit "xorl $15, %eax"))
       ((char->integer)
        (emit-expr (primcall-operand1 x))
        (emit "shrl $6, %eax"))))))
        (emit "shrl $6, %eax"))
       ((zero?)
        (emit-expr (primcall-operand1 x))
        (emit "cmpl $0,  %eax")                ; x == 0
        (emit "movl $0,  %eax")                ; zero %eax to put the result of the comparison into
        (emit "sete %al")                      ; set low byte of %eax to 1 if cmp succeeded
        (emit "sall $~a,  %eax" boolean-shift) ; construct correctly tagged boolean value
        (emit "xorl $31, %eax"))
       ))))
(define (compile-program x)
  (display ".globl scheme_entry\n\n")
@@ -54,4 +62,4 @@
  (emit-expr x)
  (emit "ret"))
(compile-program '(char->integer #\y))
(compile-program '(zero? -1))