Add tracing for syntax

mceval/syntax.rkt

@@ -1,15 +1,16 @@
 #lang sicp
 
 (#%provide (all-defined))
+(#%require racket/trace)
 
-(define (self-evaluating? exp)
+(trace-define (self-evaluating? exp)
   (cond ((number? exp) true)
         ((string? exp) true)
         ((eq? exp '*unassigned*) true)  ; Special symbol that can
                                         ; never be a variable.
         (else false)))
 
-(define (quoted? exp)
+(trace-define (quoted? exp)
   (tagged-list? exp 'quote))
 (define (text-of-quotation exp) (cadr exp))
 
@@ -18,7 +19,7 @@
       (eq? (car exp) tag)
       false))
 
-(define (variable? exp) (symbol? exp))
+(trace-define (variable? exp) (symbol? exp))
 
 ;; Assignment
 (define (assignment? exp)