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0 pointstodd88y ago0 comments

I totally understand your frustration with Haskell.

I understand the tutorials and have read though the books available, but when I try to use the language on a small real project, say a 2d barcode generator, I have trouble getting off the ground. Its not even clear to me which set of features are recommended for the language. It seems like different users program in different, incompatible, languages! Here is a list of optional language extensions supported by GHC:

Cpp

OverlappingInstances

UndecidableInstances

IncoherentInstances

UndecidableSuperClasses

MonomorphismRestriction

MonoPatBinds

MonoLocalBinds

RelaxedPolyRec

ExtendedDefaultRules

ForeignFunctionInterface

UnliftedFFITypes

InterruptibleFFI

CApiFFI

GHCForeignImportPrim

JavaScriptFFI

ParallelArrays

Arrows

TemplateHaskell

TemplateHaskellQuotes

QuasiQuotes

ImplicitParams

ImplicitPrelude

ScopedTypeVariables

AllowAmbiguousTypes

UnboxedTuples

UnboxedSums

BangPatterns

TypeFamilies

TypeFamilyDependencies

TypeInType

OverloadedStrings

OverloadedLists

NumDecimals

DisambiguateRecordFields

RecordWildCards

RecordPuns

ViewPatterns

GADTs

GADTSyntax

NPlusKPatterns

DoAndIfThenElse

RebindableSyntax

ConstraintKinds

PolyKinds

DataKinds

InstanceSigs

ApplicativeDo

StandaloneDeriving

DeriveDataTypeable

AutoDeriveTypeable

DeriveFunctor

DeriveTraversable

DeriveFoldable

DeriveGeneric

DefaultSignatures

DeriveAnyClass

DeriveLift

DerivingStrategies

TypeSynonymInstances

FlexibleContexts

FlexibleInstances

ConstrainedClassMethods

MultiParamTypeClasses

NullaryTypeClasses

FunctionalDependencies

UnicodeSyntax

ExistentialQuantification

MagicHash

EmptyDataDecls

KindSignatures

RoleAnnotations

ParallelListComp

TransformListComp

MonadComprehensions

GeneralizedNewtypeDeriving

RecursiveDo

PostfixOperators

TupleSections

PatternGuards

LiberalTypeSynonyms

RankNTypes

ImpredicativeTypes

TypeOperators

ExplicitNamespaces

PackageImports

ExplicitForAll

AlternativeLayoutRule

AlternativeLayoutRuleTransitional

DatatypeContexts

NondecreasingIndentation

RelaxedLayout

TraditionalRecordSyntax

LambdaCase

MultiWayIf

BinaryLiterals

NegativeLiterals

DuplicateRecordFields

OverloadedLabels

EmptyCase

PatternSynonyms

PartialTypeSignatures

NamedWildCards

StaticPointers

TypeApplications

Strict

StrictData

MonadFailDesugaring

I've seen different subsets of these extensions recommended. Is there some canonical subset recommended by anyone doing real work in Haskell?

Even more off topic: in reference to your note about the word "stubbornness", the word "bookkeeping" has three consecutive doubled letters. I believe that there are no examples of four consecutive doubled letters in any ordinary English dictionary, but I ought to grep the longer lexicons I've got at home.

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3 comments · 1 top-level

tome8y ago· 2 in thread

> It seems like different users program in different, incompatible, languages!

None of them are incompatible as far as I am aware. If they are, I'm sure it's in very minor ways that don't occur in practice.

todd8OP8y ago

I'm sorry, I don't understand or maybe I wasn't clear. These extensions change the meanings (semantics and syntax) of Haskell programs accepted by the compiler. A program which would normally terminate using Haskell's ordinary lazy semantics might not terminate when using the Strict extension that changes the default semantics to less lazy.

As far as I can tell from blogs like [1], the other language extensions also change the language in ways that are not forward and backward compatible with out-of-the-box Haskell.

[1] https://ocharles.org.uk/blog/

tome8y ago

You were perfectly clear, but just mostly incorrect, I think.

You are correct that Strict is a language extension that significantly changes the semantics of a Haskell program. It's a new extension so it didn't cross my mind. But besides Strict the number of extensions that change semantics of existing programs in a significant but non-forward and -backward compatible way is very, very small.

Basically, the summary of Haskell extensions is:

Around half of them are new features that should be in the language standard but aren't because a new standard hasn't been produced for years. Around half of them extend (not change) the language in powerful ways and are best avoided unless you really need them. Around Ɛ% are things that significantly change the semantics, and 0% are things that mean you're programming in a "different, incompatible, language" (all extensions are compatible across module boundaries).

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