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@ -1,6 +1,6 @@
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#lang br
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(require rackunit (for-syntax br/datum sugar/debug))
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(provide define-datatype occurs-free?)
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(require rackunit racket/struct (for-syntax br/datum sugar/debug))
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(provide define-datatype cases occurs-free?)
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#;(begin
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(struct lc-exp () #:transparent)
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@ -59,17 +59,22 @@
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(occurs-free? search-var rator)
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(occurs-free? search-var rand)))]))
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(define #'(cases-let <input-var> <subtype> (<field> ...) <body> ...)
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(inject-syntax ([#'(<subtype-field> ...) (map-syntax (λ(field) (format-datum '~a-~a #'<subtype> field)) #'(<field> ...))])
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#'(let ([<field> (<subtype-field> <input-var>)] ...)
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<body> ...)))
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(define #'(cases <base-type> <input-var> [<subtype> (<field> ...) <body> ...] ...)
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(define-syntax (cases stx)
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(syntax-case stx (else)
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[(_ <base-type> <input-var>
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[<subtype> (<positional-var> ...) <body> ...] ...
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[else <else-body> ...])
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(inject-syntax ([#'(<subtype?> ...) (map-syntax (λ(s) (format-datum '~a? s)) #'(<subtype> ...))])
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#'(cond
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[(<subtype?> <input-var>) (cases-let <input-var> <subtype> (<field> ...) <body> ...)] ...)))
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[(<subtype?> <input-var>) (match-let ([(list <positional-var> ...) (struct->list <input-var>)])
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<body> ...)] ...
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[else <else-body> ...]))]
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[(_ <base-type> <input-var>
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<subtype-case> ...)
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#'(cases <base-type> <input-var>
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<subtype-case> ...
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[else (void)])]))
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(define (occurs-free? search-var exp)
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(cases lc-exp exp
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