100 lines
2.4 KiB
Racket
100 lines
2.4 KiB
Racket
#lang racket/base
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(require "typed-structs.rkt")
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(provide parse)
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(define (parse exp)
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(cond
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[(self-evaluating? exp)
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(make-Constant exp)]
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[(quoted? exp)
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(make-Quote (text-of-quotation exp))]
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[(variable? exp)
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(make-Var exp)]
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[(assignment? exp)
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(make-Assign (assignment-variable exp)
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(parse (assignment-value exp)))]
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[(definition? exp)
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(make-Def (definition-variable exp)
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(parse (definition-value exp)))]
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[(if? exp)
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(make-Branch (parse (if-predicate exp))
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(parse (if-consequent exp))
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(parse (if-alternative exp)))]
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[(lambda? exp)
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(make-Lam (lambda-parameters exp)
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(map parse (lambda-body exp)))]
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[(begin? exp)
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(make-Seq (map parse (begin-actions exp)))]
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[(application? exp)
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(make-App (parse (operator exp))
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(map parse (operands exp)))]
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[else
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(error 'compile "Unknown expression type ~e" exp)]))
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;; expression selectors
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(define (self-evaluating? exp)
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(cond
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[(number? exp) #t]
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[(string? exp) #t]
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[else #f]))
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(define (variable? exp) (symbol? exp))
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(define (quoted? exp) (tagged-list? exp 'quote))
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(define (text-of-quotation exp) (cadr exp))
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(define (tagged-list? exp tag)
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(if (pair? exp)
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(eq? (car exp) tag)
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#f))
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(define (assignment? exp)
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(tagged-list? exp 'set!))
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(define (assignment-variable exp) (cadr exp))
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(define (assignment-value exp) (caddr exp))
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(define (definition? exp)
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(tagged-list? exp 'define))
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(define (definition-variable exp)
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(if (symbol? (cadr exp))
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(cadr exp)
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(caadr exp)))
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(define (definition-value exp)
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(if (symbol? (cadr exp))
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(caddr exp)
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(make-lambda (cdadr exp)
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(cddr exp))))
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(define (lambda? exp)
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(tagged-list? exp 'lambda))
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(define (lambda-parameters exp) (cadr exp))
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(define (lambda-body exp) (cddr exp))
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(define (make-lambda parameters body)
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(cons 'lambda (cons parameters body)))
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(define (if? exp)
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(tagged-list? exp 'if))
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(define (if-predicate exp)
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(cadr exp))
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(define (if-consequent exp)
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(caddr exp))
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(define (if-alternative exp)
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(if (not (null? (cdddr exp)))
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(cadddr exp)
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'false))
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(define (begin? exp)
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(tagged-list? exp 'begin))
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(define (begin-actions exp) (cdr exp))
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(define (application? exp) (pair? exp))
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(define (operator exp) (car exp))
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(define (operands exp) (cdr exp))
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