Parser

An easy to use general-purpose parser for Elm.

This library aims to provide a clean and intuitive parsing library with good error messages out of the box.

ℹ️ This has been inspired by the elm/parser and dasch/parser libraries.

How to use

A good place to start is by defining the data type you want to parse into. Then, it's a good idea to define a function to parse into that data type.

Here's a simple example to parse an 2D point, like (42, 3.14).

import Parser exposing (Parser, drop, into, parse, succeed, take)
import Parser.Char exposing (char)
import Parser.Common exposing (number, spaces)
import Parser.Error

type alias Point =
    { x : Float
    , y : Float
    }

point : Parser Point
point =
    into "Point"
        (succeed Point
            |> drop (char '(')
            |> drop spaces
            |> take number
            |> drop spaces
            |> drop (char ',')
            |> drop spaces
            |> take number
            |> drop spaces
            |> drop (char ')')
        )

-- Here's how a successful parse looks like.
parse "(2.71, 3.14)" point --> Ok {x = 2.71, y = 3.14}

-- And we can get a nice error message if it fails.
point
    |> parse "(2.71, x)"
    |> Result.mapError (Parser.Error.dump "filename.txt")
--> Err
-->     [ "[ERROR] filename.txt:1:8: I was expecting a digit [0-9]. I got stuck when I got the character 'x'."
-->     , "  in Point at line 1:1"
-->     , ""
-->     , "1|(2.71, x)"
-->     , "  ~~~~~~~^"
-->     ]

Usage

For more detailed documentation of the functions available an code examples on how to use them, check the modules:

• Parser -- Basic functions on creating and chaining parsers.
• Parser.Common -- Common parsers like parsing integers and numbers.
• Parser.Sequence -- Sequences of parsers.
• Parser.Expression -- Expressions with operator precedence.
• Parser.Check -- Checking and lookaheads without consuming inputs.
• Parser.Error -- Functions for error reporting and formatting.