25 lines
639 B
Scheme
25 lines
639 B
Scheme
#lang scheme
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(require (lib "matrix-sig.ss" "htdp")
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(lib "matrix-render-sig.ss" "htdp")
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(lib "matrix-unit.ss" "htdp"))
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(define render@
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(unit (import)
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(export matrix-render^)
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(define-struct invisible (matrix))
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(define visible? invisible?)
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(define make-visible make-invisible)
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(define visible-matrix invisible-matrix)))
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(define invisible-matrix@
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(compound-unit
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(import)
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(export m)
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(link (((r : matrix-render^)) render@)
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(((m : matrix^)) matrix@ r))))
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(define-values/invoke-unit invisible-matrix@ (import) (export matrix^))
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(provide-signature-elements matrix^)
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