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RegExp: Nested subtractions are translated wrongly to Alex #256

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andreasabel opened this issue May 4, 2019 · 1 comment
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RegExp: Nested subtractions are translated wrongly to Alex #256

andreasabel opened this issue May 4, 2019 · 1 comment
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bug Haskell LBNF Concerning the LBNF syntax and its checking lexer Concerning the generated lexer
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2.8.4

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@andreasabel
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LBNF does not support nested subtraction in regexps, like in

token Name (char - [ "(){};.@\"" ] - [ " \n\t" ]) + ;

It works with parentheses:

token Name ((char - [ "(){};.@\"" ]) - [ " \n\t" ]) + ;

This is translated to Alex as

(($u # [\( \) \{ \} \; \. \@ \"]) # [\  \n \t]) +

which is rejected by Alex. However, Alex supports it without parentheses:

($u # [\( \) \{ \} \; \. \@ \"] # [\  \n \t]) +

Both BNFC and Alex are behaving silly here, I must say.
andreasabel added a commit that referenced this issue Dec 15, 2019
@andreasabel
[ #256 #276 ] test case
187d825
@andreasabel andreasabel self-assigned this Dec 15, 2019
@andreasabel andreasabel added this to the 2.8.4 milestone Dec 15, 2019
@andreasabel andreasabel added the lexer Concerning the generated lexer label Dec 15, 2019
@andreasabel
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Fixes:

  • BNFC now accepts left-nested subtraction without parentheses.
  • Regex are simplified before passed to the backends.

@andreasabel andreasabel added the LBNF Concerning the LBNF syntax and its checking label Dec 15, 2019
@andreasabel andreasabel mentioned this issue Dec 17, 2019
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bug Haskell LBNF Concerning the LBNF syntax and its checking lexer Concerning the generated lexer
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