# Katydid [![Build Status](https://travis-ci.org/katydid/katydid-haskell.svg?branch=master)](https://travis-ci.org/katydid/katydid-haskell) A Haskell implementation of Katydid. This includes: - [Relapse](https://katydid.github.io/katydid-haskell/Relapse.html): Validation Language - Parsers: [JSON](https://katydid.github.io/katydid-haskell/Json.html) and [XML](https://katydid.github.io/katydid-haskell/Xml.html) [Documentation for katydid](http://katydid.github.io/) [Documentation for katydid-haskell](https://katydid.github.io/katydid-haskell/) [Documentation for katydid-haskell/Relapse](https://katydid.github.io/katydid-haskell/Relapse.html) All JSON and XML tests from [the language agnostic test suite](https://github.com/katydid/testsuite) [passes]. [Hackage](https://hackage.haskell.org/package/katydid-0.1.0.0). ## Example Validating a single structure can be done using the validate function: ```haskell validate :: Tree t => Refs -> [t] -> Bool ``` , where a tree is a class in the [Parsers](https://katydid.github.io/katydid-haskell/Parsers.html) module: ```haskell class Tree a where getLabel :: a -> Label getChildren :: a -> [a] ``` Here is an example that validates a single JSON tree: ```haskell main = either (\err -> putStrLn $ "error:" ++ err) (\valid -> if valid then putStrLn "dragons exist" else putStrLn "dragons are fictional" ) $ Relapse.validate <$> runExcept (Relapse.parseGrammar ".DragonsExist == true") <*> Json.decodeJSON "{\"DragonsExist\": false}" ``` ## Efficiency If you want to validate multiple trees using the same grammar then the filter function does some internal memoization, which makes a huge difference. ```haskell filter :: Tree t => Refs -> [[t]] -> [[t]] ```