48 lines
1.3 KiB
Racket
48 lines
1.3 KiB
Racket
#lang racket
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(provide Int Prim Var Var-name Let Program interp-RVar-class interp-RVar)
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(require racket/fixnum)
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(require racket/dict)
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(require racket/struct)
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(struct Int (value) #:transparent)
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(struct Var (name) #:transparent)
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(struct Prim (op args) #:transparent)
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(struct Let (var expr body) #:transparent)
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(struct Program (info body) #:transparent)
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(define interp-RVar-class
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(class object%
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(super-new)
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(define/public ((interp-exp env) exp)
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(match exp
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[(Int n) n]
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[(Var name) (eval-symbol env name)]
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[(Prim 'read '()) (read-fixnum)]
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[(Prim '- (list e)) (fx- 0 ((interp-exp env) e))]
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[(Prim '+ `(,e1 ,e2)) (fx+ ((interp-exp env) e1) ((interp-exp env) e2))]
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[(Let var rexp body)
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(let ([value ((interp-exp env) rexp)])
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((interp-exp (dict-set env var value)) body))]))
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(define/public (interp-program program)
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(match program
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[(Program _ body) ((interp-exp (make-immutable-hash)) 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 (eval-symbol env s)
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(if (dict-has-key? env s)
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(dict-ref env s)
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(error "Symbol " s " not found")))
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(define (interp-RVar program)
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(send (new interp-RVar-class) interp-program program))
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