| License | BSD-3-Clause |
|---|---|
| Maintainer | Jamie Willis, Gigaparsec Maintainers |
| Stability | stable |
| Safe Haskell | Safe |
| Language | Haskell2010 |
Text.Gigaparsec.Position
Description
This module contains parsers that provide a way to extract position information during parsing.
Position parsers can be important for when the final result of the parser needs to encode position information for later consumption:
this is particularly useful for abstract syntax trees.
Offset is also exposed by this interface (via offset), which may be useful for establishing a caret size in specialised error messages.
Documentation
Position
The position of a parser determines where in the input stream the next character is to be consumed.
This position is defined in terms of the line (see line) and column (see col) numbers at which the character occurs in the input text.
To simply see how many characters total have been parsed, see offset.
type Pos = (Word, Word) Source #
A type representing the position of a parser in terms of line and column numbers.
This parser returns the current line number (starting at 1) of the input without having any other effect.
When this combinator is ran, no input is required, nor consumed, and the current line number will always be successfully returned. It has no other effect on the state of the parser.
Since: 0.3.0.0
This parser returns the current column number (starting at 1) of the input without having any other effect.
When this combinator is run, no input is required, nor consumed, and the current column number will always be successfully returned. It has no other effect on the state of the parser. @since 0.3.0.0
This parser returns the current line and column numbers (starting at 1) of the input without having any other effect.
When this combinator is ran, no input is required, nor consumed, and the current line and column number will always be successfully returned. It has no other effect on the state of the parser. @since 0.3.0.0
Offset & Width
offset and withWidth allow one to calculate how much input has been consumed by a parser.
This parser returns the current offset - the total number of characters consumed - into the input (starting at 0) without having any other effect.
When this combinator is ran, no input is required, nor consumed, and the current offset into the input will always be successfully returned. It has no other effect on the state of the parser.
Arguments
| :: Parsec a | the parser whose width we wish to compute |
| -> Parsec (a, Word) | a parser that pairs the result of the parser |
This combinator returns the result of a given parser p and the number of characters it consumed.
First records the initial offset on entry to given parser p, then executes p.
If p succeeds, then the offset is taken again, and the two values are subtracted to give width w.
The result, x, of p is returned along with w as the pair (x, w).
If p fails, this combinator will also fail.