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8745 :: Questions on Nim's grammar

• lyhokia (orginal) [2021-12-27T09:48:53+01:00] view original

  1. I notice that Nim's grammar has this rule:

  
  castExpr = 'cast' ('[' optInd typeDesc optPar ']' '(' optInd expr optPar ')') /
  Run

  An ordered choice followed by nothing, can anyone tell me what this means?

  2. What does \\ mean in nim's grammar? I don't find any interpretations. Does this mean the operator except(i.e. A - B matches iff A matches but B fails) in EBNF?

  Thanks a lot!

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• lyhokia (orginal) [2021-12-27T09:51:23+01:00] view original

  Q1 is solved, I scan through nim's compiler/parser.nim and found these comments:

  #| castExpr = 'cast' ('[' optInd typeDesc optPar ']' '(' optInd expr optPar ')') /
    #                    ('(' optInd exprColonEqExpr optPar ')')
  Run

  Thus this should be a typo.

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• lyhokia (orginal) [2021-12-27T09:54:21+01:00] view original

  BTW, why there is brackets needed to enclose the words, isn't / has a lower precedance than concatenation?

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• Araq (orginal) [2021-12-27T12:02:48+01:00] view original

  Brackets are used in an attempt to improve readability. The \\ are typos and should be /. Fixed here.

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• lyhokia (orginal) [2021-12-29T11:58:49+01:00] view original

  Got it, thanks!

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• lyhokia (orginal) [2021-12-29T12:17:55+01:00] view original

  I found another problem:

  
    #| literal = | INT_LIT | INT8_LIT | INT16_LIT | INT32_LIT | INT64_LIT
    #|           | UINT_LIT | UINT8_LIT | UINT16_LIT | UINT32_LIT | UINT64_LIT
    #|           | FLOAT_LIT | FLOAT32_LIT | FLOAT64_LIT
    #|           | STR_LIT | RSTR_LIT | TRIPLESTR_LIT
    #|           | CHAR_LIT | CUSTOM_NUMERIC_LIT
    #|           | NIL
  Run

  There seems to be an extra "|" in the front of literal's derivation because they can't be nil.

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• Araq (orginal) [2021-12-29T12:20:37+01:00] view original

  Correct. :-)

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• lyhokia (orginal) [2021-12-29T12:58:20+01:00] view original

  BTW, I think it's better if you could clarify the precedence of operators in the manual, I see this:

  
  tupleDecl = 'tuple'
      '[' optInd  (identColonEquals (comma/semicolon)?)*  optPar ']' |
      COMMENT? (IND{>} identColonEquals (IND{=} identColonEquals)*)?
  Run

  which obviously, means:

  
  tupleDecl = 'tuple' (
      '[' optInd  (identColonEquals (comma/semicolon)?)*  optPar ']' |
      COMMENT? (IND{>} identColonEquals (IND{=} identColonEquals)*)? )
  Run

  But you didn't clarify how indent should work..

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• AmjadBHD (orginal) [2021-12-30T08:29:31+01:00] view original

  https://github.com/nim-lang/Nim/issues/15963

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