19 lines
739 B
Scheme
19 lines
739 B
Scheme
;; Supported by core PLT, with a slight difference in how a guard is used:
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#lang scheme/base
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(define make-parameter*
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(let ([make-parameter
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(case-lambda
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[(v) (make-parameter v)]
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[(v guard) (make-parameter (if (and (procedure? guard)
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(procedure-arity-includes? guard 1))
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;; apply guard to initial value:
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(guard v)
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;; let `make-parameter' complain:
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v)
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guard)])])
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make-parameter))
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(provide (rename-out [make-parameter* make-parameter])
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parameterize)
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