elm/parser

Regular expressions are quite confusing and difficult to use. This library provides a coherent alternative that handles more cases and produces clearer code.
(Readme.md from the package)
type alias Point =
  { x : Float
  , y : Float
  }
​
point : Parser Point
point =
  succeed Point
    |. symbol "("
    |. spaces
    |= float
    |. spaces
    |. symbol ","
    |. spaces
    |= float
    |. spaces
    |. symbol ")"
This is a summary of the talk Demystifying Parsers by Tereza Sokol.
Basics
Function
Description
 run : Parser a -> String -> Result (List DeadEnd) a
Runs the Parser on a String
 int : Parser Int
Parser for Int
 float : Parser Float
Parser for Float
 oneOf : List (Parser a) -> Parser a
Trys different Parsers. Uses the first that succeeds.
Once the parser matches the first element, there is no going back!
 andThen : (a -> Parser b) -> Parser a -> Parser b
Applys the first parser and if successful applies the second. Fails if one of the parsers fails.
Pipeline
This subject is explained at 4:48 in the Video.
Function
Description
 succeed : a -> Parser a
Starts the Pipeline. a -> Parser a  is the constructor.
For a record Point use the structur called Point .
 (|=) : Parser (a -> b) -> Parser a -> Parser b
Keeps an element.
 (|.) : Parser keep -> Parser ignore -> Parser keep
Eats a character and throws it away.
 spaces : Parser ()
Represents whitespace
Strings
This subject is explained at 7:20 in the Video.
Function
Description
 chompWhile : (Char -> Bool) -> Parser ()
Looks for zero or more characters that succeeds the check. Stops as soon as the check fails.
 chompIf : (Char -> Bool) -> Parser ()
Reads one symbols.
 getChompedString : Parser a -> Parser String
Returnes the string that got chomped
Loops
This subject is explained at 14:10 in the Video.
Function
Description
 loop : state -> (state -> Parser (Step state a)) -> Parser a
Takes an initial state and a parser step and returns a parser. 
type Step state a = Loop state | Done a
A parser step just specifies if it should continue looping or stop.
Error messages
This subject is explained at 17:04 in the Video.
Function
Description
 problem : String -> Parser a
Returns the error message and ends the parsing. The argument is the actuall message.
Further Reading
🎥Video: Demystifying Parsers by Tereza Sokol
📄Thread: Elm parser question​

Recipes - Previous

Future topics

Next - Frameworks and packages

mdgriffith/elm-ui

Last modified 2yr ago

Copy link

On this page

Basics

Pipeline

Strings

Loops

Error messages