yesodweb/persistent

derivePersistField phantom type support

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#1,137 opened on Oct 23, 2020

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 (8 comments) (0 reactions) (1 assignee)Haskell (302 forks)auto 404
Feature Requestgood first issue

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Description

Phantom types are very useful for tagging things on type level, but at the moment this code will not compile

-- @Employment.hs
{-# LANGUAGE TemplateHaskell #-}
module Employment where

import Database.Persist.TH
import Prelude

data Employment a = Employed | Unemployed | Retired
    deriving (Show, Read, Eq)
derivePersistField "Employment a"

Contributor guide

Research direction
Explore the TemplateHaskell code for derivePersistField to understand how it currently handles type parameters, and determine how to modify it to support phantom type parameters.
Tech stack
haskell
Domain
backend
Issue type
Bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
Half day
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
Haskell
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
30