+(define (ast-type x)
+ (define (builtin? x)
+ (case x
+ ('+ #t)
+ ('- #t)
+ ('* #t)
+ ('! #t)
+ ('= #t)
+ ('bool->int #t)
+ (else #f)))
+ (cond
+ ((list? x)
+ (case (car x)
+ ('if 'if)
+ ('let 'let)
+ ('lambda 'lambda)
+ ('closure 'closure) ; only available in codegen
+ (else 'app)))
+ ((builtin? x) 'builtin)
+ ((symbol? x) 'var)
+ ((integer? x) 'int-literal)
+ ((boolean? x) 'bool-literal)))