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34 lines
895 B
34 lines
895 B
2 years ago
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Exercise 4.54: If we had not realized that
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require could be implemented as an ordinary procedure that uses
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amb, to be defined by the user as part of a nondeterministic program, we
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would have had to implement it as a special form. This would require syntax
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procedures
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(define (require? exp)
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(tagged-list? exp 'require))
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(define (require-predicate exp)
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(cadr exp))
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and a new clause in the dispatch in analyze
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((require? exp) (analyze-require exp))
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as well the procedure analyze-require that handles require
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expressions. Complete the following definition of analyze-require.
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(define (analyze-require exp)
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(let ((pproc (analyze
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(require-predicate exp))))
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(lambda (env succeed fail)
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(pproc env
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(lambda (pred-value fail2)
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(if ⟨??⟩
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⟨??⟩
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(succeed 'ok fail2)))
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fail))))
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