`define-extended-language`+ overriding a `variable-not-otherwise-mentioned` with a `variable-not-in` fails.
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- Dominant language
- Racket
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- 112
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Description
The program
#lang racket
(require redex/reduction-semantics)
(define-language L
(v ::= GO WAIT x)
(x ::= variable-not-otherwise-mentioned))
(define-extended-language L+ L
(x ::= (variable-not-in WAIT)))
(redex-match? L+ x (term GO))
produces #f, despite x in L+ being specified to only exclude WAIT.
It produces #t if the variable-not-in is replace with variable.
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Research direction
Start by reproducing the supplied program and tracing define-extended-language, variable-not-in, and redex-match? in the Redex implementation. Compare the extended grammar's handling of x with the original variable-not-otherwise-mentioned rule; done means the example's redex-match? result is #t while WAIT remains excluded.
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Assessment
- Domain
- compilers
- Issue type
- Bug
- Difficulty
- 3/5
- Estimated time
- 1-2 days
- Activity status
- Stale
- Clarity
- Clearly specified
- Newbie friendliness
- 45/100