35 lines
1.6 KiB
Markdown
35 lines
1.6 KiB
Markdown
generic-syntax-expanders
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========================
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A Racket package for creating macros with built-in support for defining sub-macros within them, similar to match expanders
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Sometimes complex Racket macros need a way for their syntax to be extended. The Racket match form is an example, new patterns can be created for match using define-match-expander. This racket package provides a form for defining a macro with the ability to define expanders for the macro. Consider this contrived example:
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(define-syntax call-each
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(syntax-parser
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[(_ f (expr ...))
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#'(begin (f expr) ...)]))
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(call-each displayln (1 2 3))
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If a user of this macro wished for a way to specify a range of numbers as the arguments, the user must define their own version of call-each with support for ranges that expands to using the original call-each. However, this racket package provides a form, define-syntax-with-expanders:
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(require generic-syntax-expanders
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(for-syntax racket/list))
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(define-syntax-with-expanders call-each
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(syntax-parser
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[(_ f (expr ...))
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#'(begin (f expr) ... )]))
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(define-call-each-expander foo
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(syntax-parser
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[(_ low:number high:number)
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#`(#,@(range (syntax-e #'low) (syntax-e #'high)))]))
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(call-each displayln (foo 1 4))
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The define-syntax-with-expanders form creates a define-call-each-expander form, which defines syntax transformers that are only used inside the body of a call-each form and expand before call-each does.
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You can install this package with `raco package install generic-syntax-expanders`.
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