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

#lang br
(provide b-expr b-sum b-product b-neg b-expt)

(define (b-expr expr)
  (if (integer? expr) (inexact->exact expr) expr))

(define-macro-cases b-sum
  [(_ VAL) #'VAL]
  [(_ LEFT "+" RIGHT) #'(+ LEFT RIGHT)]
  [(_ LEFT "-" RIGHT) #'(- LEFT RIGHT)])

(define-macro-cases b-product
  [(_ VAL) #'VAL]
  [(_ LEFT "*" RIGHT) #'(* LEFT RIGHT)]
  [(_ LEFT "/" RIGHT) #'(/ LEFT RIGHT 1.0)]
  [(_ LEFT "mod" RIGHT) #'(modulo LEFT RIGHT)])

(define-macro-cases b-neg
  [(_ VAL) #'VAL]
  [(_ "-" VAL) #'(- VAL)])

(define-macro-cases b-expt
  [(_ VAL) #'VAL]
  [(_ LEFT "^" RIGHT) #'(expt LEFT RIGHT)])

(define (b-not expr) (if (zero? expr) 1 0))

(define-macro (b-def ID VAR EXPR)
  #'(set! ID (λ (VAR) EXPR)))