Multiple function definitions with template haskell

Question

Suppose I have a data type like so:

data Color = Red | Blue | Green

How would I generate a function like this using templatehaskell?

myShow Red   = ...
myShow Blue  = ...
myShow Green = ...

i.e. I'm looking for multiple definitions for a function based on pattern-matching.

user2407038 · Accepted Answer · 2014-05-01 01:57:47Z

3

{-# LANGUAGE TemplateHaskell #-}

module Test where 

import Language.Haskell.TH

data Color = Red | Blue | Green

myShow' :: Q [Dec]
myShow' = return [FunD (mkName "myShow") [mkClause 'Red, mkClause 'Blue, mkClause 'Green]]
  where mkClause n = Clause [ConP n []] (NormalB $ LitE $ StringL $ nameBase n) []

answered May 1, 2014 at 1:57

user2407038

14.7k3 gold badges31 silver badges45 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Vlad the Impala Over a year ago

This put me on the right track. I ended up using a lambda with a case expression like so: myShow = return $ LamE [VarP mc] (CaseE (VarE mc) $ [Match ...] where mc = mkName "mc"

Collectives™ on Stack Overflow

Multiple function definitions with template haskell

1 Answer 1

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related