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typesetting/pitfall/sugar/case.rkt

17 lines
666 B
Racket

#lang racket/base
(require (for-syntax racket/base racket/syntax br/syntax) br/define)
(provide (all-defined-out))
(define-macro (define-case-macro ID PRED)
#'(define-macro-cases ID
[(_ TEST-VAL [(MATCH0 . MATCH-VALS) . RESULT] (... ...) [else . ELSE-RESULT])
#'(cond
[(PRED TEST-VAL '(MATCH0 . MATCH-VALS)) . RESULT] (... ...)
[else . ELSE-RESULT])]
[(_ TEST-VAL MATCH-CLAUSE (... ...))
#'(ID TEST-VAL
MATCH-CLAUSE (... ...)
[else (error 'ID (format "no match for ~a" TEST-VAL))])]))
;; like case but strictly uses `eq?` comparison (as opposed to `equal?`)
(define-case-macro caseq memq)