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46 lines
1.9 KiB
Racket
46 lines
1.9 KiB
Racket
#lang racket/base
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;; Changes the default behavior of #%top.
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;; Unbound identifiers are allowed, and treated as the
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;; tag in a txexpr (with the rest of the expression treated as the body)
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;; To suppress this behavior, use def/c to wrap any name.
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;; If that name isn't already defined, you'll get the usual syntax error.
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(require (for-syntax racket/base))
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(provide (except-out (all-defined-out) top~)
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(rename-out (top~ #%top)))
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;; Allow tag attributes to be specified as follows:
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;; @foo['shape: "square" 'color: "red"]{hello}
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(define-syntax-rule (top~ . id)
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(λ x
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(define reversed-pieces ; list of attribute pairs, and last element holds a list of everything else, then reversed
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(reverse (let chomp ([x x])
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(define result+regexp (and ((length x) . >= . 2)
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(symbol? (car x))
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;; accept strings only
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;; numbers are difficult because they don't parse as cleanly.
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;; string will read as a string even if there's no space to the left.
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(or (string? (cadr x)))
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;; Looking for symbol ending with a colon
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(regexp-match #rx"^(.*?):$" (symbol->string (car x)))))
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(if result+regexp
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; reuse result value. cadr is first group in match.
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(cons (list (string->symbol (cadr result+regexp))(cadr x)) (chomp (cddr x)))
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(list x)))))
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(define-values (body attrs) (if (equal? null reversed-pieces)
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(values null null)
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(values (car reversed-pieces) (cdr reversed-pieces))))
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`(id ,@(if (equal? attrs null) null (list (reverse attrs))) ,@body)))
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(define-syntax (def/c stx)
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(syntax-case stx ()
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[(_ x)
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(if (identifier-binding #'x )
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#'x
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#'(#%top . x))]))
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