katydid: A haskell implementation of Katydid

[ bsd3, data, library, program ] [ Propose Tags ]

A haskell implementation of Katydid

This includes:

You should only need the following modules:

If you want to implement your own parser then you can look at the Parsers module

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Change log changelog.md
Dependencies base (>=4.7 && <5), bytestring, containers, deepseq, either, extra, hxt, ilist, json, katydid, mtl, parsec, regex-tdfa, text, transformers [details]
License BSD-3-Clause
Copyright Walter Schulze
Author Walter Schulze
Maintainer awalterschulze@gmail.com
Category Data
Home page https://github.com/katydid/katydid-haskell
Source repo head: git clone https://github.com/katydid/katydid-haskell
Uploaded by awalterschulze at Tue May 15 12:40:20 UTC 2018
Distributions LTSHaskell:, NixOS:, openSUSE:
Executables katydid-exe
Downloads 477 total (33 in the last 30 days)
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Status Docs not available [build log]
All reported builds failed as of 2018-05-15 [all 3 reports]
Hackage Matrix CI


  • Ast
  • Derive
  • Expr
  • Exprs
    • Exprs.Compare
    • Exprs.Contains
    • Exprs.Elem
    • Exprs.Length
    • Exprs.Logic
    • Exprs.Strings
    • Exprs.Type
    • Exprs.Var
  • IfExprs
  • Json
  • MemDerive
  • Parser
  • Parsers
  • Relapse
  • Simplify
  • Smart
  • VpaDerive
  • Xml
  • Zip


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For package maintainers and hackage trustees

Readme for katydid-

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Build Status

A Haskell implementation of Katydid.

Katydid Logo

This includes:

Documentation for katydid

Documentation for katydid-haskell

Documentation for katydid-haskell/Relapse

All JSON and XML tests from the language agnostic test suite [passes].



Validating a single structure can be done using the validate function:

validate :: Tree t => Grammar -> [t] -> Bool

, where a tree is a class in the Parsers module:

class Tree a where
    getLabel :: a -> Label
    getChildren :: a -> [a]

Here is an example that validates a single JSON tree:

main = either 
    (\err -> putStrLn $ "error:" ++ err) 
    (\valid -> if valid 
        then putStrLn "dragons exist" 
        else putStrLn "dragons are fictional"
    ) $
    Relapse.validate <$> 
        Relapse.parse ".DragonsExist == true" <*> 
        Json.decodeJSON "{\"DragonsExist\": false}"


If you want to validate multiple trees using the same grammar then the filter function does some internal memoization, which makes a huge difference.

filter :: Tree t => Grammar -> [[t]] -> [[t]]

User Defined Functions

If you want to create your own extra functions for operating on the leaves, then you can inject them into the parse function:

main = either
    (\err -> putStrLn $ "error:" ++ err)
    (\valid -> if valid
        then putStrLn "prime birthday !!!"
        else putStrLn "JOMO"
    ) $
    Relapse.validate <$>
        Relapse.parseWithUDFs userLib ".Survived->isPrime($int)" <*>
        Json.decodeJSON "{\"Survived\": 104743}"

Defining your own user library to inject is easy. The Expr library provides many useful helper functions:

import Data.Numbers.Primes (isPrime)
import Expr

userLib :: String -> [AnyExpr] -> Either String AnyExpr
userLib "isPrime" args = mkIsPrime args
userLib n _ = throwError $ "undefined function: " ++ n

mkIsPrime :: [AnyExpr] -> Either String AnyExpr
mkIsPrime args = do {
    arg <- assertArgs1 "isPrime" args;
    mkBoolExpr . isPrimeExpr <$> assertInt arg;

isPrimeExpr :: Integral a => Expr a -> Expr Bool
isPrimeExpr numExpr = trimBool Expr {
    desc = mkDesc "isPrime" [desc numExpr]
    , eval = \fieldValue -> isPrime <$> eval numExpr fieldValue


  • Protobuf parser
  • Profile and Optimize (bring up to par with Go version)
  • Typed DSL (Combinator)