define-union-language behavior examples

gistfile1.txt

#lang racket
(require redex)

(define-language L1
  (a integer)
  (e variable-not-otherwise-mentioned
     (* e e)))

(define-language L2
  (b string)
  (e integer
     (+ e e)))

(define-union-language Merged L1 L2)
(define-union-language TaggedUnion (L1. L1) (L2. L2))

(redex-match Merged e (term (+ 1 x)))
(redex-match TaggedUnion e (term (+ 1 x)))
(redex-match TaggedUnion e (term (* 1 x)))
(redex-match TaggedUnion a (term 1))
(redex-match TaggedUnion L1.a (term 1))

; define-union-language can be internal, but has to be done with
; names that are already defined as languages
; not allowed:
#; (define (foo x y t)
     (define-union-language temp-lang x y)
     (redex-match temp-lang e t))
; allowed:
(define (foo x y t)
    (define-union-language temp-lang L1 L2)
    (redex-match temp-lang e t))