25 lines
798 B
Scheme
25 lines
798 B
Scheme
#lang scheme
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(require htdp/big-draw
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htdp/draw-sig
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mzlib/unit)
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(define-syntax (draw s)
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(syntax-case s (produce)
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[(_ stmt ... produce exp) (syntax (begin (and stmt ...) exp))]
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[(_ stmt ... produce)
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(raise-syntax-error #f "produce must be followed by an expression" s)]
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[(_ stmt ... produce exp exp2)
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(raise-syntax-error #f "produce must be followed by exactly one expression" s)]
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[(_ stmt ... produce exp exp2 exp3)
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(raise-syntax-error #f "produce must be followed by exactly one expression" s)]
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[(_ stmt ...)
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(raise-syntax-error #f "use drawing instructions between _draw_ and _produce_ and an expression behind produce" s)]
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))
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(provide
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draw ;; (draw <expression> ... produce <expression>)
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)
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(provide-signature-elements draw^)
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