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- #lang racket
- (require racket/match)
- (define builtins
- `((car . ,car)
- (cdr . ,cdr)
- (cons . ,cons)
- (+ . ,+)
- (- . ,-)
- (* . ,*)
- (/ . ,/)))
- (define special-forms
- '(lambda))
- (define (i exp env spec)
- (match exp
- ((? number? n) n)
- ((? symbol? s)
- (cond ((assoc s env) => cdr)
- (else (error "unbound variable" s))))
- ((? list? l)
- (if (member (car l) spec)
- (i-special l env spec)
- (apply (i (car l) env spec)
- (map (lambda (exp) (i exp env spec)) (cdr l)))))
- (else (error "unknown expression type" exp))))
- (define (i-special exp env spec)
- (match exp
- (`(lambda (,x) ,b)
- (lambda (y)
- (i b (cons (cons x y) env) (remove x spec))))
- (else (error "Unimplemented special form:" exp))))
- ;; > (i '(+ 7 (car (cons 3 5))) builtins)
- ;; 10
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