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beautiful-racket/beautiful-racket-demo/basic-demo-2/if.rkt

28 lines
834 B
Racket

8 years ago
#lang br
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(require "go.rkt")
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(provide b-if b-comp-expr b-logic-expr)
;; b-if : /"if" b-expr /"then" b-expr [/"else" b-expr]
(define (b-if cond-expr then-expr [else-expr #f])
(cond
[(not (zero? cond-expr)) (b-goto then-expr)]
[else-expr => b-goto]))
(define bool-int (λ (val) (if val 1 0)))
(define bi= (compose1 bool-int =))
(define bi< (compose1 bool-int <))
(define bi> (compose1 bool-int >))
;; b-comp-expr : b-cond-expr [("and" | "or") b-cond-expr]
(define-macro-cases b-logic-expr
[(_ ARG) #'ARG]
[(_ LEFT "and" RIGHT) #'(and LEFT RIGHT)]
[(_ LEFT "or" RIGHT) #'(or LEFT RIGHT)])
;; b-cond-expr : b-expr [("=" | "<" | ">") b-expr]
(define-macro-cases b-comp-expr
[(_ ARG) #'ARG]
[(_ LEFT "=" RIGHT) #'(bi= LEFT RIGHT)]
[(_ LEFT "<" RIGHT) #'(bi< LEFT RIGHT)]
[(_ LEFT ">" RIGHT) #'(bi> LEFT RIGHT)])