141 lines
3.7 KiB
Scheme
141 lines
3.7 KiB
Scheme
;;; Hygienic Macros
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(define-library (picrin macro)
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(import (picrin base))
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;; assumes no derived expressions are provided yet
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(define (walk proc expr)
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"walk on symbols"
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(if (null? expr)
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'()
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(if (pair? expr)
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(cons (walk proc (car expr))
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(walk proc (cdr expr)))
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(if (vector? expr)
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(list->vector (walk proc (vector->list expr)))
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(if (symbol? expr)
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(proc expr)
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expr)))))
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(define (memoize f)
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"memoize on symbols"
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(define cache (make-dictionary))
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(lambda (sym)
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(call-with-values (lambda () (dictionary-ref cache sym))
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(lambda (value exists)
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(if exists
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value
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(begin
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(define val (f sym))
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(dictionary-set! cache sym val)
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val))))))
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(define (make-syntactic-closure env free form)
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(define resolve
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(memoize
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(lambda (sym)
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(make-identifier sym env))))
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(walk
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(lambda (sym)
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(if (memq sym free)
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sym
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(resolve sym)))
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form))
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(define (close-syntax form env)
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(make-syntactic-closure env '() form))
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(define-syntax capture-syntactic-environment
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(lambda (form use-env mac-env)
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(list (cadr form) (list (make-identifier 'quote mac-env) mac-env))))
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(define (sc-macro-transformer f)
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(lambda (expr use-env mac-env)
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(make-syntactic-closure mac-env '() (f expr use-env))))
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(define (rsc-macro-transformer f)
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(lambda (expr use-env mac-env)
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(make-syntactic-closure use-env '() (f expr mac-env))))
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(define (er-macro-transformer f)
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(lambda (expr use-env mac-env)
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(define rename
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(memoize
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(lambda (sym)
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(make-identifier sym mac-env))))
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(define (compare x y)
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(if (not (symbol? x))
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#f
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(if (not (symbol? y))
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#f
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(identifier=? use-env x use-env y))))
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(f expr rename compare)))
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(define (ir-macro-transformer f)
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(lambda (expr use-env mac-env)
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(define icache* (make-dictionary))
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(define inject
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(memoize
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(lambda (sym)
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(define id (make-identifier sym use-env))
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(dictionary-set! icache* id sym)
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id)))
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(define rename
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(memoize
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(lambda (sym)
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(make-identifier sym mac-env))))
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(define (compare x y)
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(if (not (symbol? x))
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#f
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(if (not (symbol? y))
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#f
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(identifier=? mac-env x mac-env y))))
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(walk (lambda (sym)
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(call-with-values (lambda () (dictionary-ref icache* sym))
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(lambda (value exists)
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(if exists
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value
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(rename sym)))))
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(f (walk inject expr) inject compare))))
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(define (strip-syntax form)
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(walk ungensym form))
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(define-syntax define-macro
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(er-macro-transformer
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(lambda (expr r c)
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(define formal (car (cdr expr)))
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(define body (cdr (cdr expr)))
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(if (symbol? formal)
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(list (r 'define-syntax) formal
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(list (r 'lambda) (list (r 'form) '_ '_)
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(list (r 'apply) (car body) (list (r 'cdr) (r 'form)))))
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(list (r 'define-macro) (car formal)
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(cons (r 'lambda)
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(cons (cdr formal)
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body)))))))
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(export identifier?
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identifier=?
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make-identifier
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make-syntactic-closure
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close-syntax
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capture-syntactic-environment
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sc-macro-transformer
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rsc-macro-transformer
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er-macro-transformer
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ir-macro-transformer
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strip-syntax
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define-macro))
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