30 lines
645 B
Racket
30 lines
645 B
Racket
#lang racket
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(require racket/fixnum)
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(provide Int Prim Program interp-Lint)
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(struct Int (value))
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(struct Prim (op args))
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(struct Program (info body))
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(define (read-fixnum)
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(let ([r (read)])
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(cond
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[(fixnum? r) r]
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[else (error "invalid fixnum in input: " r)])))
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(define (interp-exp sexp)
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(match sexp
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[(Int n) n]
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[(Prim 'read '()) (read-fixnum)]
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[(Prim '- (list e)) (fx- 0 (interp-exp e))]
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[(Prim '- (list e1 e2)) (fx- (interp-exp e1) (interp-exp e2))]
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[(Prim '+ (list e1 e2)) (fx+ (interp-exp e1) (interp-exp e2))]))
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(define (interp-Lint p)
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(match p
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[(Program '() body) (interp-exp body)]))
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