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10541 :: Having trouble initializing my parser

• JustinWayland (orginal) [2023-10-10T04:54:54+02:00] view original

  I have a file that looks like this:

  import std/[lexbase, streams]
  
  type
      UpdateParserState = enum
          startState, statePlainText, statePotentialExpansion
      UpdateParser = object of BaseLexer
          curtext: string
          state: UpdateParserState
  
  func open(my: var UpdateParser, input: Stream) =
      ## Opens update parser
      lexbase.open(my, input)
      my.curtext = ""
      my.state = startState
  Run

  Attempting to compile just this results in the following error:

  
  expandupdate.nim(10, 6) Error: 'open' can have side effects
  > expandupdate.nim(12, 17) Hint: 'open' calls `.sideEffect` 'open'
  >> .../nim/lib/pure/lexbase.nim(137, 6) Hint: 'open' called by 'open'
  Run

  What am I doing wrong compared to the parsers in the standard library?

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• Araq (orginal) [2023-10-10T05:54:52+02:00] view original

  Use:

  proc open(my: var UpdateParser, input: Stream) =
  
  Run

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• PMunch (orginal) [2023-10-10T09:37:08+02:00] view original

  To explain what's going on here you declared your open as a func instead of a proc. In Nim a func is closer to a pure mathematical function, or the functions found in functional programming languages. They can't do IO, they can't read global state, etc. A procedure in Nim is what your probably used to as a "function" in languages like C and JavaScript.

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• JustinWayland (orginal) [2023-10-10T20:33:38+02:00] view original

  Oops. Somehow I managed to dodge this in the last program I wrote, but not this time. At least I learned something important today.

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