Position line and column should start at zero

[jamesdbrock]

Position line and column should start at 0, not 1.

purescript-parsing/src/Text/Parsing/Parser/Pos.purs

Line 26 in f8dae05

initialPos = Position { line: 1, column: 1 }

This has been super inconvenient for me on several occasions.

https://www.cs.utexas.edu/users/EWD/transcriptions/EWD08xx/EWD831.html

This would be an easy change to make, but the hard part would be not breaking downstream dependents.

[jamesdbrock]

Actually what would be better is to add a field to Position

initialPos  = Position { line: 1, column: 1, offset: 0 }

so then we can track both the lines-based and offset-based positions.

From an API perspective, it is too easy for a library user to construct this Position with an invalid state.

On the other hand, it was already easy for the library user to construct an invalid state, since for each line
of input, a different range of columns is valid.

Perhaps it would be better to instead add

newtype Offset = Offset Int

initialOffset  = Offset 0

offset :: forall s m. Monad m => ParserT s m Offset

[thomashoneyman]

Thanks for opening this issue @jamesdbrock. I’m not personally familiar with the background behind why this library starts at 1, so I’m going to defer to other maintainers on that. But just wanted to let you know this was seen!