Parsing Expression Grammar (PEG) in Elm. github 
, package by Romāns Potašovs
# Getting Started
To get started with Elm PEG Parser, you first need to Define a PEG Grammar using the Grammar type. Once you have defined your grammar, you can use the parse function to parse input text using the grammar.
import Html import Peg exposing (Error, fromString, parse) grammarString : String grammarString = """ start <- <digit+> {action} digit <- [0-9] """ {-| Parse a string with the grammar -} result : Result Error String result = let actions _ found _ = Ok found predicate _ _ state = ( True, state ) in grammarString |> fromString |> Result.andThen (\grammar -> parse grammar "" actions predicate "123") {-| Check if the parse succeeded -} main = case result of Ok value -> Html.text ("Parsed value: " ++ value) Err error -> Html.text ("Parse error: " ++ error.message)
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Adding Actions to a PEG Grammar post by Guido van Rossum
In the provided Elm code, the `{action}` placeholder in the grammar does not have a specific processing step associated with it. Instead, it's a placeholder that can be used to denote where a custom action would be performed if needed. In this code, the `{action}` is just part of the grammar rule, but it doesn't have any specific processing step defined within the Elm code. It's up to the developer to provide the actual action that should be taken when a match occurs. In the provided code, the action placeholder `{action}` is present in the `start` rule, but no specific processing step is defined for it within the Elm code. If you wanted to perform a specific action when a match occurs, you would need to replace `{action}` with the actual code for that action. For example: […] (ChatGPT September 25 Version)
In your Elm code, the `actions` function is defined like this: ```elm actions _ found _ = Ok found ``` This function is called when a match occurs. It takes three arguments: `left`, `found`, and `right`. In this case, it simply returns `Ok found`, where `found` is the matched text. The placeholder `{action}` in the grammar corresponds to the part of the grammar where you might want to perform a custom action. In your Elm code, this action is defined in the `actions` function. If you want to perform a different action, you would modify the `actions` function accordingly. For example, if you wanted to transform the matched text before returning it, you would do so within the `actions` function.