diff --git a/CHANGELOG.md b/CHANGELOG.md new file mode 100644 --- /dev/null +++ b/CHANGELOG.md @@ -0,0 +1,19 @@ +# Changelog for `from` + +All notable changes to this project should be documented in this file. + +The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/), and this project adheres to the [Haskell Package Versioning Policy](https://pvp.haskell.org/). + +## Unreleased + +(no changes yet) + +## 1.0.0.0 - 2025-10-24 + +Initial release. + +- Added typeclasses `From` and `TryFrom`. +- Added instances of `From` for some fundamental type-mappings in `base`: + - All types in `Data.Int` and `Data.Word` can be both the source and the destination of the conversion. + - The types `Float` and `Double` can be the destination, but not the source. So `from :: Int32 -> Float` exists, while `from :: Float -> Int32` does not. + - That's it. We begin with minimal instances intentionally. For example, there is no `instance From Int String`. This is because it is tricky (often impossible) to selectively import instances, especially when the module dependency graph is complicated. We'd need to be careful about adding instances. diff --git a/LICENSE b/LICENSE new file mode 100644 --- /dev/null +++ b/LICENSE @@ -0,0 +1,202 @@ + + Apache License + Version 2.0, January 2004 + http://www.apache.org/licenses/ + + TERMS AND CONDITIONS FOR USE, REPRODUCTION, AND DISTRIBUTION + + 1. Definitions. + + "License" shall mean the terms and conditions for use, reproduction, + and distribution as defined by Sections 1 through 9 of this document. + + "Licensor" shall mean the copyright owner or entity authorized by + the copyright owner that is granting the License. + + "Legal Entity" shall mean the union of the acting entity and all + other entities that control, are controlled by, or are under common + control with that entity. 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For the general rationale behind this idea, see `README.md` under the project root. + +This Haskell library package provides the `From` and `TryFrom` typeclasses. + +The `From` typeclass provides `from :: a -> b`. It is an interface for types that can be converted from/to each other. + +The `TryFrom` typeclass provides `tryFrom :: a -> Maybe b`. It is an interface for types that can be converted from/to each other, with the possibility of a failure. + +This package has **1** dependency: base. + +## Instances + +It is well known that it is difficult to "selectively" import/export typeclass instances. Therefore, we need to be careful about what instances to provide by default. + +There are base functions, some of them even in `Prelude`, that basically serve as a less general version of `from`. Examples include `fromIntegral` and `fromEnum`. However, naively defining `instance (Integral a, Num b) => From a b` and `instance (Enum a) => From a Int` will quickly lead us to trouble: + +``` + • Overlapping instances for From Int16 Int + arising from a use of ‘from’ + Matching instances: + instance (Integral a, Num b) => From a b + instance Enum a => From a Int + ... +``` + +Therefore, this package does not provide such "contextual" instances. (Of course, you may define them in your application project, if you want.) + +Instead, concrete instances are provided. For example, all pairs (excluding self to self) of these integral types are instantiated using `fromIntegral`: + +- `Int` +- `Integer` +- `Int8` +- `Int16` +- `Int32` +- `Int64` +- `Word8` +- `Word16` +- `Word32` +- `Word64` + +Each type can be both source and destination of `from`. Additional types are instantiated as destination-only: + +- `Float` +- `Double` diff --git a/Setup.hs b/Setup.hs new file mode 100644 --- /dev/null +++ b/Setup.hs @@ -0,0 +1,3 @@ +import Distribution.Simple + +main = defaultMain diff --git a/from.cabal b/from.cabal new file mode 100644 --- /dev/null +++ b/from.cabal @@ -0,0 +1,71 @@ +cabal-version: 1.12 + +-- This file has been generated from package.yaml by hpack version 0.37.0. +-- +-- see: https://github.com/sol/hpack + +name: from +version: 1.0.0.0 +synopsis: Typeclasses for type conversion mappings +description: This package provides the typeclasses 'From' and 'TryFrom'. + . + The 'From.From' typeclass provides @'From.from' :: a -> b@. It is an + interface a pair of types that can be converted from one to another. + . + The 'From.TryFrom' typeclass provides @'From.tryFrom' :: a -> 'Prelude.Maybe' + b@. It is an interface for a pair of types that can be converted from one to + another, safely handling the possibility of a failure. + . + Default 'From.From' instances are provided for some integral types in base, + using 'Prelude.fromIntegral'. + . + This is the core package. This package itself is not spectacularly useful. + One example of immediate usefulness would be the @from-string@ package. + . + If you are interested, you may want to check the project @README.md@ (not the + package @README.md@) as well. +category: Typeclass +homepage: https://codeberg.org/xt/from +bug-reports: https://codeberg.org/xt/from/issues +author: XT +maintainer: git@xtendo.org +copyright: Copyright (C) 2024-2025 XT +license: Apache-2.0 +license-file: LICENSE +build-type: Simple +extra-source-files: + README.md + CHANGELOG.md + +source-repository head + type: git + location: https://codeberg.org/xt/from + +library + exposed-modules: + From + other-modules: + From.Classes + From.Num + Paths_from + hs-source-dirs: + src + ghc-options: -Wall -Wcompat -Widentities -Wincomplete-record-updates -Wincomplete-uni-patterns -Wmissing-export-lists -Wmissing-home-modules -Wpartial-fields -Wredundant-constraints + build-depends: + base >=4.7 && <5 + default-language: Haskell2010 + +test-suite from-test + type: exitcode-stdio-1.0 + main-is: Main.hs + other-modules: + Paths_from + hs-source-dirs: + test + ghc-options: -Wall -Wcompat -Widentities -Wincomplete-record-updates -Wincomplete-uni-patterns -Wmissing-export-lists -Wmissing-home-modules -Wpartial-fields -Wredundant-constraints + build-depends: + base >=4.7 && <5 + , bytestring + , rawfilepath + , unix + default-language: Haskell2010 diff --git a/src/From.hs b/src/From.hs new file mode 100644 --- /dev/null +++ b/src/From.hs @@ -0,0 +1,80 @@ +-- | +-- Module : From +-- Copyright : (C) 2024-2025 XT et al. +-- License : Apache-2.0 (see the LICENSE file) +-- Portability : FlexibleInstances, MultiParamTypeClasses +-- +-- This module provides the 'From' and 'TryFrom' typeclasses. +-- +-- The 'From.From' typeclass provides +-- +-- @ +-- 'From.from' :: a -> b +-- @ +-- +-- for types that can be converted from/to each other. +-- +-- The 'From.TryFrom' typeclass provides +-- +-- @ +-- 'From.tryFrom' :: a -> 'Prelude.Maybe' b +-- @ +-- +-- for types that can be converted from/to each other, handling the possibility +-- of a failure. +-- +-- == About default instances +-- +-- Default 'From' instances are provided for the following types in base: +-- +-- * 'Int' +-- +-- * 'Integer' +-- +-- * t'Data.Int.Int8' +-- +-- * t'Data.Int.Int16' +-- +-- * t'Data.Int.Int32' +-- +-- * t'Data.Int.Int64' +-- +-- * t'Data.Word.Word8' +-- +-- * t'Data.Word.Word16' +-- +-- * t'Data.Word.Word32' +-- +-- * t'Data.Word.Word64' +-- +-- Any pair of the above types (except self-self) are convertible using 'from'. +-- In addition to that, the above types can also be converted to 'Float' or +-- 'Double' using 'from'. The implementation uses 'fromIntegral'. +-- +-- There are other possible default instances, like +-- +-- @ +-- 'Char' -> 'Int' +-- @ +-- +-- (using 'Data.Char.chr') or +-- +-- @ +-- 'Foreign.Ptr.Ptr' a -> 'Foreign.Ptr.Ptr' b +-- @ +-- +-- (using 'Foreign.Ptr.castPtr'), but we plan to carefully examine and discuss +-- before adding them, as it is difficult to selectively import/export +-- typeclass instances. +-- +-- Separate packages will also provide useful instances, like @from-string@. +module From ( + -- ** From + From (..), + + -- ** TryFrom + TryFrom (..), +) where + +import From.Classes +import From.Num () diff --git a/src/From/Classes.hs b/src/From/Classes.hs new file mode 100644 --- /dev/null +++ b/src/From/Classes.hs @@ -0,0 +1,15 @@ +{-# LANGUAGE MultiParamTypeClasses #-} + +module From.Classes ( + From (..), + TryFrom (..), +) where + +-- | The type conversion class where conversion is (mostly) safe and expected +-- to be successful. +class From a b where + from :: a -> b + +-- | The type conversion class where conversion can fail +class TryFrom a b where + tryFrom :: a -> Maybe b diff --git a/src/From/Num.hs b/src/From/Num.hs new file mode 100644 --- /dev/null +++ b/src/From/Num.hs @@ -0,0 +1,448 @@ +{-# LANGUAGE MultiParamTypeClasses #-} +{-# OPTIONS_GHC -Wno-orphans #-} + +module From.Num () where + +import Data.Int +import Data.Word +import From.Classes + +-- | Implementation is 'fromIntegral' +instance From Int Integer where + from = fromIntegral + +-- | Implementation is 'fromIntegral' +instance From Int Int8 where + from = fromIntegral + +-- | Implementation is 'fromIntegral' +instance From Int Int16 where + from = fromIntegral + +-- | Implementation is 'fromIntegral' +instance From Int Int32 where + from = fromIntegral + +-- | Implementation is 'fromIntegral' +instance From Int Int64 where + from = fromIntegral + +-- | Implementation is 'fromIntegral' +instance From Int Word8 where + from = fromIntegral + +-- | Implementation is 'fromIntegral' +instance From Int Word16 where + from = fromIntegral + +-- | Implementation is 'fromIntegral' +instance From Int Word32 where + from = fromIntegral + +-- | Implementation is 'fromIntegral' +instance From Int Word64 where + from = fromIntegral + +-- | Implementation is 'fromIntegral' +instance From Int Float where + from = fromIntegral + +-- | Implementation is 'fromIntegral' +instance From Int Double where + from = fromIntegral + +-- | Implementation is 'fromIntegral' +instance From Integer Int where + from = fromIntegral + +-- | Implementation is 'fromIntegral' +instance From Integer Int8 where + from = fromIntegral + +-- | Implementation is 'fromIntegral' +instance From Integer Int16 where + from = fromIntegral + +-- | Implementation is 'fromIntegral' +instance From Integer Int32 where + from = fromIntegral + +-- | Implementation is 'fromIntegral' +instance From Integer Int64 where + from = fromIntegral + +-- | Implementation is 'fromIntegral' +instance From Integer Word8 where + from = fromIntegral + +-- | Implementation is 'fromIntegral' +instance From Integer Word16 where + from = fromIntegral + +-- | Implementation is 'fromIntegral' +instance From Integer Word32 where + from = fromIntegral + +-- | Implementation is 'fromIntegral' +instance From Integer Word64 where + from = fromIntegral + +-- | Implementation is 'fromIntegral' +instance From Integer Float where + from = fromIntegral + +-- | Implementation is 'fromIntegral' +instance From Integer Double where + from = fromIntegral + +-- | Implementation is 'fromIntegral' +instance From Int8 Int where + from = fromIntegral + +-- | Implementation is 'fromIntegral' +instance From Int8 Integer where + from = fromIntegral + +-- | Implementation is 'fromIntegral' +instance From Int8 Int16 where + from = fromIntegral + +-- | Implementation is 'fromIntegral' +instance From Int8 Int32 where + from = fromIntegral + +-- | Implementation is 'fromIntegral' +instance From Int8 Int64 where + from = fromIntegral + +-- | Implementation is 'fromIntegral' +instance From Int8 Word8 where + from = fromIntegral + +-- | Implementation is 'fromIntegral' +instance From Int8 Word16 where + from = fromIntegral + +-- | Implementation is 'fromIntegral' +instance From Int8 Word32 where + from = fromIntegral + +-- | Implementation is 'fromIntegral' +instance From Int8 Word64 where + from = fromIntegral + +-- | Implementation is 'fromIntegral' +instance From Int8 Float where + from = fromIntegral + +-- | Implementation is 'fromIntegral' +instance From Int8 Double where + from = fromIntegral + +-- | Implementation is 'fromIntegral' +instance From Int16 Int where + from = fromIntegral + +-- | Implementation is 'fromIntegral' +instance From Int16 Integer where + from = fromIntegral + +-- | Implementation is 'fromIntegral' +instance From Int16 Int8 where + from = fromIntegral + +-- | Implementation is 'fromIntegral' +instance From Int16 Int32 where + from = fromIntegral + +-- | Implementation is 'fromIntegral' +instance From Int16 Int64 where + from = fromIntegral + +-- | Implementation is 'fromIntegral' +instance From Int16 Word8 where + from = fromIntegral + +-- | Implementation is 'fromIntegral' +instance From Int16 Word16 where + from = fromIntegral + +-- | Implementation is 'fromIntegral' +instance From Int16 Word32 where + from = fromIntegral + +-- | Implementation is 'fromIntegral' +instance From Int16 Word64 where + from = fromIntegral + +-- | Implementation is 'fromIntegral' +instance From Int16 Float where + from = fromIntegral + +-- | Implementation is 'fromIntegral' +instance From Int16 Double where + from = fromIntegral + +-- | Implementation is 'fromIntegral' +instance From Int32 Int where + from = fromIntegral + +-- | Implementation is 'fromIntegral' +instance From Int32 Integer where + from = fromIntegral + +-- | Implementation is 'fromIntegral' +instance From Int32 Int8 where + from = fromIntegral + +-- | Implementation is 'fromIntegral' +instance From Int32 Int16 where + from = fromIntegral + +-- | Implementation is 'fromIntegral' +instance From Int32 Int64 where + from = fromIntegral + +-- | Implementation is 'fromIntegral' +instance From Int32 Word8 where + from = fromIntegral + +-- | Implementation is 'fromIntegral' +instance From Int32 Word16 where + from = fromIntegral + +-- | Implementation is 'fromIntegral' +instance From Int32 Word32 where + from = fromIntegral + +-- | Implementation is 'fromIntegral' +instance From Int32 Word64 where + from = fromIntegral + +-- | Implementation is 'fromIntegral' +instance From Int32 Float where + from = fromIntegral + +-- | Implementation is 'fromIntegral' +instance From Int32 Double where + from = fromIntegral + +-- | Implementation is 'fromIntegral' +instance From Int64 Int where + from = fromIntegral + +-- | Implementation is 'fromIntegral' +instance From Int64 Integer where + from = fromIntegral + +-- | Implementation is 'fromIntegral' +instance From Int64 Int8 where + from = fromIntegral + +-- | Implementation is 'fromIntegral' +instance From Int64 Int16 where + from = fromIntegral + +-- | Implementation is 'fromIntegral' +instance From Int64 Int32 where + from = fromIntegral + +-- | Implementation is 'fromIntegral' +instance From Int64 Word8 where + from = fromIntegral + +-- | Implementation is 'fromIntegral' +instance From Int64 Word16 where + from = fromIntegral + +-- | Implementation is 'fromIntegral' +instance From Int64 Word32 where + from = fromIntegral + +-- | Implementation is 'fromIntegral' +instance From Int64 Word64 where + from = fromIntegral + +-- | Implementation is 'fromIntegral' +instance From Int64 Float where + from = fromIntegral + +-- | Implementation is 'fromIntegral' +instance From Int64 Double where + from = fromIntegral + +-- | Implementation is 'fromIntegral' +instance From Word8 Int where + from = fromIntegral + +-- | Implementation is 'fromIntegral' +instance From Word8 Integer where + from = fromIntegral + +-- | Implementation is 'fromIntegral' +instance From Word8 Int8 where + from = fromIntegral + +-- | Implementation is 'fromIntegral' +instance From Word8 Int16 where + from = fromIntegral + +-- | Implementation is 'fromIntegral' +instance From Word8 Int32 where + from = fromIntegral + +-- | Implementation is 'fromIntegral' +instance From Word8 Int64 where + from = fromIntegral + +-- | Implementation is 'fromIntegral' +instance From Word8 Word16 where + from = fromIntegral + +-- | Implementation is 'fromIntegral' +instance From Word8 Word32 where + from = fromIntegral + +-- | Implementation is 'fromIntegral' +instance From Word8 Word64 where + from = fromIntegral + +-- | Implementation is 'fromIntegral' +instance From Word8 Float where + from = fromIntegral + +-- | Implementation is 'fromIntegral' +instance From Word8 Double where + from = fromIntegral + +-- | Implementation is 'fromIntegral' +instance From Word16 Int where + from = fromIntegral + +-- | Implementation is 'fromIntegral' +instance From Word16 Integer where + from = fromIntegral + +-- | Implementation is 'fromIntegral' +instance From Word16 Int8 where + from = fromIntegral + +-- | Implementation is 'fromIntegral' +instance From Word16 Int16 where + from = fromIntegral + +-- | Implementation is 'fromIntegral' +instance From Word16 Int32 where + from = fromIntegral + +-- | Implementation is 'fromIntegral' +instance From Word16 Int64 where + from = fromIntegral + +-- | Implementation is 'fromIntegral' +instance From Word16 Word8 where + from = fromIntegral + +-- | Implementation is 'fromIntegral' +instance From Word16 Word32 where + from = fromIntegral + +-- | Implementation is 'fromIntegral' +instance From Word16 Word64 where + from = fromIntegral + +-- | Implementation is 'fromIntegral' +instance From Word16 Float where + from = fromIntegral + +-- | Implementation is 'fromIntegral' +instance From Word16 Double where + from = fromIntegral + +-- | Implementation is 'fromIntegral' +instance From Word32 Int where + from = fromIntegral + +-- | Implementation is 'fromIntegral' +instance From Word32 Integer where + from = fromIntegral + +-- | Implementation is 'fromIntegral' +instance From Word32 Int8 where + from = fromIntegral + +-- | Implementation is 'fromIntegral' +instance From Word32 Int16 where + from = fromIntegral + +-- | Implementation is 'fromIntegral' +instance From Word32 Int32 where + from = fromIntegral + +-- | Implementation is 'fromIntegral' +instance From Word32 Int64 where + from = fromIntegral + +-- | Implementation is 'fromIntegral' +instance From Word32 Word8 where + from = fromIntegral + +-- | Implementation is 'fromIntegral' +instance From Word32 Word16 where + from = fromIntegral + +-- | Implementation is 'fromIntegral' +instance From Word32 Word64 where + from = fromIntegral + +-- | Implementation is 'fromIntegral' +instance From Word32 Float where + from = fromIntegral + +-- | Implementation is 'fromIntegral' +instance From Word32 Double where + from = fromIntegral + +-- | Implementation is 'fromIntegral' +instance From Word64 Int where + from = fromIntegral + +-- | Implementation is 'fromIntegral' +instance From Word64 Integer where + from = fromIntegral + +-- | Implementation is 'fromIntegral' +instance From Word64 Int8 where + from = fromIntegral + +-- | Implementation is 'fromIntegral' +instance From Word64 Int16 where + from = fromIntegral + +-- | Implementation is 'fromIntegral' +instance From Word64 Int32 where + from = fromIntegral + +-- | Implementation is 'fromIntegral' +instance From Word64 Int64 where + from = fromIntegral + +-- | Implementation is 'fromIntegral' +instance From Word64 Word8 where + from = fromIntegral + +-- | Implementation is 'fromIntegral' +instance From Word64 Word16 where + from = fromIntegral + +-- | Implementation is 'fromIntegral' +instance From Word64 Word32 where + from = fromIntegral + +-- | Implementation is 'fromIntegral' +instance From Word64 Float where + from = fromIntegral + +-- | Implementation is 'fromIntegral' +instance From Word64 Double where + from = fromIntegral diff --git a/test/Main.hs b/test/Main.hs new file mode 100644 --- /dev/null +++ b/test/Main.hs @@ -0,0 +1,90 @@ +{-# LANGUAGE OverloadedStrings #-} + +module Main (main) where + +import Control.Exception +import Data.ByteString (ByteString) +import qualified Data.ByteString as B +import Data.ByteString.Builder (Builder) +import qualified Data.ByteString.Builder as B +import RawFilePath +import System.Exit +import System.IO +import System.Posix.Env.ByteString +import System.Posix.Temp.ByteString + +srcTypes :: [ByteString] +srcTypes = + [ "Int" + , "Integer" + , "Int8" + , "Int16" + , "Int32" + , "Int64" + , "Word8" + , "Word16" + , "Word32" + , "Word64" + ] + +dstTypes :: [ByteString] +dstTypes = + [ "Int" + , "Integer" + , "Int8" + , "Int16" + , "Int32" + , "Int64" + , "Word8" + , "Word16" + , "Word32" + , "Word64" + , "Float" + , "Double" + ] + +main :: IO () +main = do + args <- getArgs + let shouldKeepFile = "--keep" `elem` args + bracket acquire (release shouldKeepFile) $ \(tmpPath, hdl) -> do + B.putStr $ tmpPath <> "\n" + B.hPutBuilder hdl $ header <> mconcat instancePart + hClose hdl + diffExitCode <- + runProcess "diff" ["-u", "--color=always", tmpPath, "src/From/Num.hs"] + case diffExitCode of + ExitSuccess -> return () + _ -> exitWith diffExitCode + where + acquire = mkstemps "haskell-from-" ".hs" + release shouldKeepFile (path, hdl) + | shouldKeepFile = hClose hdl + | otherwise = hClose hdl >> removeFile path + + runProcess cmd args = startProcess (proc cmd args) >>= waitForProcess + + instanceLine src dst = + mconcat ["instance From ", B.byteString src, " ", B.byteString dst, " where\n"] + instancePart = + [ mconcat + [ "\n" + , "-- | Implementation is 'fromIntegral'\n" + , instanceLine src dst + , " from = fromIntegral\n" + ] + | src <- srcTypes + , dst <- dstTypes + , src /= dst + ] + +header :: Builder +header = + "{-# LANGUAGE MultiParamTypeClasses #-}\n\ + \{-# OPTIONS_GHC -Wno-orphans #-}\n\ + \\n\ + \module From.Num () where\n\ + \\n\ + \import Data.Int\n\ + \import Data.Word\n\ + \import From.Classes\n"