GHC

Synopsis

ghc [option|filename]
ghci [option|filename]

Description

This manual page documents briefly the ghc and ghci commands. Note that ghci is not yet available on all architectures. Extensive documentation is available in various other formats including PDF and HTML; see below.

Each of GHC’s command line options is classified as either static or dynamic. A static flag may only be specified on the command line, whereas a dynamic flag may also be given in an OPTIONS pragma in a source file or set from the GHCi command-line with :set .

As a rule of thumb, all the language options are dynamic, as are the warning options and the debugging options.

The rest are static, with the notable exceptions of -v, -cpp, -fasm, -fvia-C, -fllvm, and -#include. The OPTIONS sections lists the status of each flag.

Common suffixes of file names for Haskell are:

.hs

Haskell source code; preprocess, compile

.lhs

literate Haskell source; unlit, preprocess, compile

.hi

Interface file; contains information about exported symbols

.hc

intermediate C files

.⟨way⟩_o

object files for “way” ⟨way⟩; common ways are:

dyn

dynamically-linked

p

built with profiling

.⟨way⟩_hi

interface files for “way” ⟨way⟩; common ways are:

Options

Code generation

-fasm -fllvm -fno-code -fwrite-interface -fbyte-code -fobject-code -g⟨n⟩ -dynamic -dynamic-too

Debugging the compiler

-dcore-lint -ddump-to-file -ddump-asm -ddump-bcos -ddump-cmm-from-stg -ddump-cmm-verbose -ddump-cmm -ddump-core-stats -ddump-cse -ddump-deriv -ddump-ds -ddump-foreign -ddump-hpc -ddump-inlinings -ddump-llvm -ddump-occur-anal -ddump-opt-cmm -ddump-parsed -ddump-prep -ddump-rn -ddump-rule-firings -ddump-rule-rewrites -ddump-rules -ddump-vect -ddump-simpl -ddump-simpl-iterations -ddump-spec -ddump-splices -ddump-stg -ddump-stranal -ddump-str-signatures -ddump-tc -dth-dec-file=⟨file⟩ -ddump-types -ddump-worker-wrapper -ddump-if-trace -ddump-tc-trace -ddump-vt-trace -ddump-rn-trace -ddump-rn-stats -ddump-simpl-stats -dno-debug-output -dppr-debug -dppr-user-length -dppr-cols=⟨n⟩ -dppr-case-as-let -dsuppress-all -dsuppress-uniques -dsuppress-idinfo -dsuppress-unfoldings -dsuppress-module-prefixes -dsuppress-type-signatures -dsuppress-type-applications -dsuppress-coercions -dsource-stats -dcmm-lint -dstg-lint -dstg-stats -dverbose-core2core -dverbose-stg2stg -dshow-passes -dfaststring-stats -frule-check

C pre-processor

-cpp -D⟨symbol⟩[=⟨value⟩] -U⟨symbol⟩ -I⟨dir⟩

Finding imports

-i⟨dir⟩[:⟨dir⟩]* -i

Interactive mode

-ignore-dot-ghci -ghci-script -fbreak-on-error -fbreak-on-exception -fghci-hist-size=⟨n⟩ -fprint-evld-with-show -fprint-bind-result -fno-print-bind-contents -fno-implicit-import-qualified -interactive-print ⟨expr⟩

Interface files

-ddump-hi -ddump-hi-diffs -ddump-minimal-imports --show-iface ⟨file⟩

Keeping intermediate files

-keep-hc-file, -keep-hc-files -keep-hi-files -keep-llvm-file, -keep-llvm-files -keep-o-files -keep-s-file, -keep-s-files -keep-tmp-files

Language options

-fconstraint-solver-iterations=⟨n⟩ -freduction-depth=⟨n⟩ -fcontext-stack=⟨n⟩ -fglasgow-exts -firrefutable-tuples -fpackage-trust -ftype-function-depth=⟨n⟩ -XAllowAmbiguousTypes -XArrows -XApplicativeDo -XAutoDeriveTypeable -XBangPatterns -XBinaryLiterals -XCApiFFI -XConstrainedClassMethods -XConstraintKinds -XCPP -XDataKinds -XDefaultSignatures -XDeriveAnyClass -XDeriveDataTypeable -XDeriveFunctor -XDeriveFoldable -XDeriveGeneric -XDeriveGeneric -XDeriveLift -XDeriveTraversable -XDerivingStrategies -XDisambiguateRecordFields -XEmptyCase -XEmptyDataDecls -XExistentialQuantification -XExplicitForAll -XExplicitNamespaces -XExtendedDefaultRules -XFlexibleContexts -XFlexibleInstances -XForeignFunctionInterface -XFunctionalDependencies -XGADTs -XGADTSyntax -XGeneralizedNewtypeDeriving -XGenerics -XImplicitParams -XNoImplicitPrelude -XImpredicativeTypes -XIncoherentInstances -XTypeFamilyDependencies -XInstanceSigs -XInterruptibleFFI -XKindSignatures -XLambdaCase -XLiberalTypeSynonyms -XMagicHash -XMonadComprehensions -XMonoLocalBinds -XNoMonomorphismRestriction -XMultiParamTypeClasses -XMultiWayIf -XNamedFieldPuns -XNamedWildCards -XNegativeLiterals -XNPlusKPatterns -XNullaryTypeClasses -XNumDecimals -XOverlappingInstances -XOverloadedLabels -XOverloadedLists -XOverloadedStrings -XPackageImports -XParallelArrays -XParallelListComp -XPartialTypeSignatures -XNoPatternGuards -XPatternSynonyms -XPolyKinds -XPolymorphicComponents -XPostfixOperators -XQuasiQuotes -XRank2Types -XRankNTypes -XRebindableSyntax -XRecordWildCards -XRecursiveDo -XRoleAnnotations -XSafe -XScopedTypeVariables -XStandaloneDeriving -XStaticPointers -XStrictData -XTemplateHaskell -XTemplateHaskellQuotes -XNoTraditionalRecordSyntax -XTransformListComp -XTrustworthy -XTupleSections -XTypeFamilies -XTypeInType -XTypeOperators -XTypeSynonymInstances -XUnboxedTuples -XUnboxedSums -XUndecidableInstances -XUnicodeSyntax -XUnliftedFFITypes -XUnsafe -XViewPatterns

Linking options

-shared -staticlib -fPIC -fPIE -pie -dynload -framework ⟨name⟩ -framework-path ⟨dir⟩ -l ⟨lib⟩ -L ⟨dir⟩ -main-is ⟨thing⟩ --mk-dll -no-hs-main -rtsopts[=⟨none|some|all⟩] -with-rtsopts=⟨opts⟩ -no-rtsopts-suggestions -no-link -split-objs -split-sections -static -threaded -debug -ticky -eventlog -fno-gen-manifest -fno-embed-manifest -fno-shared-implib -dylib-install-name ⟨path⟩ -rdynamic

Miscellaneous options

-j[⟨n⟩] -fno-hi-version-check -fhistory-size -fno-ghci-history -fno-ghci-sandbox -flocal-ghci-history

Modes of operation

--help,-? --interactive --make -e ⟨expr⟩ --show-iface ⟨file⟩ -M --frontend ⟨module⟩ --supported-extensions, --supported-languages --show-options --info --version, -V --numeric-version --print-libdir

Individual optimizations

-fcall-arity -fcase-merge -fcase-folding -fcmm-elim-common-blocks -fcmm-sink -fcpr-anal -fcse -fdicts-cheap -fdicts-strict -fdmd-tx-dict-sel -fdo-eta-reduction -fdo-lambda-eta-expansion -feager-blackholing -fenable-rewrite-rules -fexcess-precision -fexpose-all-unfoldings -ffloat-in -ffull-laziness -ffun-to-thunk -fignore-asserts -fignore-interface-pragmas -flate-dmd-anal -fliberate-case -fliberate-case-threshold=⟨n⟩ -floopification -fmax-inline-alloc-size=⟨n⟩ -fmax-inline-memcpy-insns=⟨n⟩ -fmax-inline-memset-insns=⟨n⟩ -fmax-relevant-binds=⟨n⟩ -fmax-uncovered-patterns=⟨n⟩ -fmax-simplifier-iterations=⟨n⟩ -fmax-worker-args=⟨n⟩ -fno-opt-coercion -fno-pre-inlining -fno-state-hack -fomit-interface-pragmas -fomit-yields -foptimal-applicative-do -fpedantic-bottoms -fregs-graph -fregs-iterative -fsimplifier-phases=⟨n⟩ -fsimpl-tick-factor=⟨n⟩ -fspec-constr -fspec-constr-count=⟨n⟩ -fspec-constr-threshold=⟨n⟩ -fspecialise -fcross-module-specialise -fstatic-argument-transformation -fstrictness -fstrictness-before=⟨n⟩ -funbox-small-strict-fields -funbox-strict-fields -funfolding-creation-threshold=⟨n⟩ -funfolding-dict-discount=⟨n⟩ -funfolding-fun-discount=⟨n⟩ -funfolding-keeness-factor=⟨n⟩ -funfolding-use-threshold=⟨n⟩ -fvectorisation-avoidance -fvectorise -fworker-wrapper

Optimization levels

-O0 -O, -O1 -O2 -Odph

Package options

-this-unit-id ⟨unit-id⟩ -package ⟨pkg⟩ -hide-all-packages -hide-package ⟨pkg⟩ -ignore-package ⟨pkg⟩ -package-db ⟨file⟩ -clear-package-db -no-global-package-db -global-package-db -no-user-package-db -user-package-db -no-auto-link-packages -trust ⟨pkg⟩ -distrust ⟨pkg⟩ -distrust-all -package-env ⟨file⟩|⟨name⟩

Phases of compilation

-F -E -C -S -c -x ⟨suffix⟩

Overriding external programs

-pgmL ⟨cmd⟩ -pgmP ⟨cmd⟩ -pgmc ⟨cmd⟩ -pgmlo ⟨cmd⟩ -pgmlc ⟨cmd⟩ -pgms ⟨cmd⟩ -pgma ⟨cmd⟩ -pgml ⟨cmd⟩ -pgmdll ⟨cmd⟩ -pgmF ⟨cmd⟩ -pgmwindres ⟨cmd⟩ -pgmlibtool ⟨cmd⟩

Phase-specific options

-optL ⟨option⟩ -optP ⟨option⟩ -optF ⟨option⟩ -optc ⟨option⟩ -optlo ⟨option⟩ -optlc ⟨option⟩ -opta ⟨option⟩ -optl ⟨option⟩ -optdll ⟨option⟩ -optwindres ⟨option⟩

Platform-specific options

-msse2 -msse4.2

Compiler plugins

-fplugin=⟨module⟩ -fplugin-opt=⟨module⟩:⟨args⟩

Profiling

-prof -fprof-auto -fprof-auto-top -fprof-auto-exported -fprof-cafs -fno-prof-count-entries -ticky

Program coverage

-fhpc -hpcdir ⟨dir⟩

Recompilation checking

-fforce-recomp

Redirecting output

-hcsuf ⟨suffix⟩ -hidir ⟨dir⟩ -hisuf ⟨suffix⟩ -o ⟨file⟩ -odir ⟨dir⟩ -ohi ⟨file⟩ -osuf ⟨suffix⟩ -stubdir ⟨dir⟩ -dumpdir ⟨dir⟩ -outputdir ⟨dir⟩ -dyno ⟨file⟩ -dynosuf ⟨suffix⟩ -dynhisuf ⟨suffix⟩

Temporary files

-tmpdir ⟨dir⟩

Verbosity options

-v -v ⟨n⟩ -fhide-source-paths -fprint-potential-instances -fprint-explicit-foralls -fprint-explicit-kinds -fprint-explicit-runtime-reps -fprint-unicode-syntax -fprint-expanded-synonyms -fprint-typechecker-elaboration -fdiagnostics-color=(always|auto|never) -f[no-]diagnostics-show-caret -ferror-spans -Rghc-timing -fshow-hole-constraints -fshow-loaded-modules

Warnings

-W -w -Wall -Wcompat -Werror -Werror=⟨wflag⟩ -Wwarn -Wwarn=⟨wflag⟩ -Wunrecognised-warning-flags -fshow-warning-groups -fdefer-type-errors -fdefer-typed-holes -fdefer-out-of-scope-variables -fhelpful-errors -freverse-errors -fmax-errors -Wdeprecated-flags -Wduplicate-constraints -Wduplicate-exports -Whi-shadowing -Widentities -Wimplicit-prelude -Wincomplete-patterns -Wincomplete-uni-patterns -fmax-pmcheck-iterations=⟨n⟩ -Wincomplete-record-updates -Wmissing-fields -Wmissing-import-lists -Wmissing-methods -Wmissing-signatures -Wmissing-exported-sigs -Wmissing-exported-signatures -Wmissing-local-sigs -Wmissing-local-signatures -Wmissing-monadfail-instances -Wsemigroup -Wmissed-specialisations -Wall-missed-specialisations -Wmonomorphism-restriction -Wname-shadowing -Wnoncanonical-monad-instances -Wnoncanonical-monadfail-instances -Wnoncanonical-monoid-instances -Worphans -Woverlapping-patterns -Wtabs -Wtype-defaults -Wunrecognised-pragmas -Wunticked-promoted-constructors -Wunused-binds -Wunused-top-binds -Wunused-local-binds -Wunused-pattern-binds -Wunused-imports -Wunused-matches -Wunused-foralls -Wunused-type-variables -Wunused-do-bind -Wwrong-do-bind -Wunsafe -Wsafe -Wtrustworthy-safe -Wwarnings-deprecations -Wdeprecations -Wamp -Wredundant-constraints -Wdeferred-type-errors -Wtyped-holes -Wdeferred-out-of-scope-variables -Wpartial-type-signatures -Wderiving-typeable -Wmissing-home-modules

Code generation

-fasm

Use the native code generator

-fllvm

Compile using the LLVM code generator

-fno-code

Omit code generation

-fwrite-interface

Always write interface files

-fbyte-code

Generate byte-code

-fobject-code

Generate object code

-g⟨n⟩

Produce DWARF debug information in compiled object files.⟨n⟩ can be 0, 1, or 2, with higher numbers producing richer output. If ⟨n⟩ is omitted level 2 is assumed.

-dynamic

Build dynamically-linked object files and executables

-dynamic-too

Build dynamic object files as well as static object files during compilation

Debugging the compiler

-dcore-lint

Turn on internal sanity checking

-ddump-to-file

Dump to files instead of stdout

-ddump-asm

Dump assembly

-ddump-bcos

Dump interpreter byte code

-ddump-cmm-from-stg

Dump STG-to-C– output

-ddump-cmm-verbose

Show output from each C– pipeline pass

-ddump-cmm

Dump the final C– output

-ddump-core-stats

Print a one-line summary of the size of the Core program at the end of the optimisation pipeline

-ddump-cse

Dump CSE output

-ddump-deriv

Dump deriving output

-ddump-ds

Dump desugarer output

-ddump-foreign

Dump foreign export stubs

-ddump-hpc

Dump after instrumentation for program coverage

-ddump-inlinings

Dump inlining info

-ddump-llvm

Dump LLVM intermediate code. Implies -fllvm.

-ddump-occur-anal

Dump occurrence analysis output

-ddump-opt-cmm

Dump the results of C– to C– optimising passes

-ddump-parsed

Dump parse tree

-ddump-prep

Dump prepared core

-ddump-rn

Dump renamer output

-ddump-rule-firings

Dump rule firing info

-ddump-rule-rewrites

Dump detailed rule firing info

-ddump-rules

Dump rules

-ddump-vect

Dump vectoriser input and output

-ddump-simpl

Dump final simplifier output

-ddump-simpl-iterations

Dump output from each simplifier iteration

-ddump-spec

Dump specialiser output

-ddump-splices

Dump TH spliced expressions, and what they evaluate to

-ddump-stg

Dump final STG

-ddump-stranal

Dump strictness analyser output

-ddump-str-signatures

Dump strictness signatures

-ddump-tc

Dump typechecker output

-dth-dec-file=⟨file⟩

Show evaluated TH declarations in a .th.hs file

-ddump-types

Dump type signatures

-ddump-worker-wrapper

Dump worker-wrapper output

-ddump-if-trace

Trace interface files

-ddump-tc-trace

Trace typechecker

-ddump-vt-trace

Trace vectoriser

-ddump-rn-trace

Trace renamer

-ddump-rn-stats

Renamer stats

-ddump-simpl-stats

Dump simplifier stats

-dno-debug-output

Suppress unsolicited debugging output

-dppr-debug

Turn on debug printing (more verbose)

-dppr-user-length

Set the depth for printing expressions in error msgs

-dppr-cols=⟨n⟩

Set the width of debugging output. For example -dppr-cols200

-dppr-case-as-let

Print single alternative case expressions as strict lets.

-dsuppress-all

In core dumps, suppress everything (except for uniques) that is suppressible.

-dsuppress-uniques

Suppress the printing of uniques in debug output (easier to use diff)

-dsuppress-idinfo

Suppress extended information about identifiers where they are bound

-dsuppress-unfoldings

Suppress the printing of the stable unfolding of a variable at its binding site

-dsuppress-module-prefixes

Suppress the printing of module qualification prefixes

-dsuppress-type-signatures

Suppress type signatures

-dsuppress-type-applications

Suppress type applications

-dsuppress-coercions

Suppress the printing of coercions in Core dumps to make them shorter

-dsource-stats

Dump haskell source stats

-dcmm-lint

C– pass sanity checking

-dstg-lint

STG pass sanity checking

-dstg-stats

Dump STG stats

-dverbose-core2core

Show output from each core-to-core pass

-dverbose-stg2stg

Show output from each STG-to-STG pass

-dshow-passes

Print out each pass name as it happens

-dfaststring-stats

Show statistics for fast string usage when finished

-frule-check

Report sites with rules that could have fired but didn’t. Takes a string argument.

C pre-processor

-cpp

Run the C pre-processor on Haskell source files

-D⟨symbol⟩[=⟨value⟩]

Define a symbol in the C pre-processor

-U⟨symbol⟩

Undefine a symbol in the C pre-processor

-I⟨dir⟩

Add ⟨dir⟩ to the directory search list for #include files

Finding imports

-i⟨dir⟩[:⟨dir⟩]*

add ⟨dir⟩, ⟨dir2⟩, etc. to import path

-i

Empty the import directory list

Interactive mode

-ignore-dot-ghci

Disable reading of .ghci files

-ghci-script

Read additional .ghci files

-fbreak-on-error

Break on uncaught exceptions and errors

-fbreak-on-exception

Break on any exception thrown

-fghci-hist-size=⟨n⟩

Set the number of entries GHCi keeps for :history. See The GHCi Debugger.

-fprint-evld-with-show

Enable usage of Show instances in :print. See Breakpoints and inspecting variables.

-fprint-bind-result

Turn on printing of binding results in GHCi

-fno-print-bind-contents

Turn off printing of binding contents in GHCi

-fno-implicit-import-qualified

Turn off implicit qualified import of everything in GHCi

-interactive-print ⟨expr⟩

Select the function to use for printing evaluated expressions in GHCi

Interface files

-ddump-hi

Dump the new interface to stdout

-ddump-hi-diffs

Show the differences vs. the old interface

-ddump-minimal-imports

Dump a minimal set of imports

--show-iface ⟨file⟩

See Modes of operation.

Keeping intermediate files

-keep-hc-file, -keep-hc-files

Retain intermediate .hc files.

-keep-hi-files

Retain intermediate .hi files (the default).

-keep-llvm-file, -keep-llvm-files

Retain intermediate LLVM .ll files. Implies -fllvm.

-keep-o-files

Retain intermediate .o files (the default).

-keep-s-file, -keep-s-files

Retain intermediate .s files.

-keep-tmp-files

Retain all intermediate temporary files.

Language options

-fconstraint-solver-iterations=⟨n⟩

default: 4. Set the iteration limit for the type-constraint solver. Typically one iteration suffices; so please yell if you find you need to set it higher than the default. Zero means infinity.

-freduction-depth=⟨n⟩

default: 200. Set the limit for type simplification. Zero means infinity.

-fcontext-stack=⟨n⟩

Deprecated. Use -freduction-depth=⟨n⟩ instead.

-fglasgow-exts

Deprecated. Enable most language extensions; see Language options for exactly which ones.

-firrefutable-tuples

Make tuple pattern matching irrefutable

-fpackage-trust

Enable Safe Haskell trusted package requirement for trustworthy modules.

-ftype-function-depth=⟨n⟩

Deprecated. Use -freduction-depth=⟨n⟩ instead.

-XAllowAmbiguousTypes

Allow the user to write ambiguous types, and the type inference engine to infer them.

-XArrows

Enable arrow notation extension

-XApplicativeDo

Enable Applicative do-notation desugaring

-XAutoDeriveTypeable

As of GHC 7.10, this option is not needed, and should not be used. Previously this would automatically derive Typeable instances for every datatype and type class declaration. Implies -XDeriveDataTypeable.

-XBangPatterns

Enable bang patterns.

-XBinaryLiterals

Enable support for binary literals.

-XCApiFFI

Enable the CAPI calling convention.

-XConstrainedClassMethods

Enable constrained class methods.

-XConstraintKinds

Enable a kind of constraints.

-XCPP

Enable the C preprocessor.

-XDataKinds

Enable datatype promotion.

-XDefaultSignatures

Enable default signatures.

-XDeriveAnyClass

Enable deriving for any class.

-XDeriveDataTypeable

Enable deriving for the Data class. Implied by -XAutoDeriveTypeable.

-XDeriveFunctor

Enable deriving for the Functor class. Implied by -XDeriveTraversable.

-XDeriveFoldable

Enable deriving for the Foldable class. Implied by -XDeriveTraversable.

-XDeriveGeneric

Enable deriving for the Generic class.

-XDeriveGeneric

Enable deriving for the Generic class.

-XDeriveLift

Enable deriving for the Lift class

-XDeriveTraversable

Enable deriving for the Traversable class. Implies -XDeriveFunctor and -XDeriveFoldable.

-XDerivingStrategies

Enables deriving strategies.

-XDisambiguateRecordFields

Enable record field disambiguation. Implied by -XRecordWildCards.

-XEmptyCase

Allow empty case alternatives.

-XEmptyDataDecls

Enable empty data declarations.

-XExistentialQuantification

Enable existential quantification.

-XExplicitForAll

Enable explicit universal quantification. Implied by -XScopedTypeVariables, -XLiberalTypeSynonyms, -XRankNTypes and -XExistentialQuantification.

-XExplicitNamespaces

Enable using the keyword type to specify the namespace of entries in imports and exports (Explicit namespaces in import/export). Implied by -XTypeOperators and -XTypeFamilies.

-XExtendedDefaultRules

Use GHCi’s extended default rules in a normal module.

-XFlexibleContexts

Enable flexible contexts. Implied by -XImplicitParams.

-XFlexibleInstances

Enable flexible instances. Implies -XTypeSynonymInstances. Implied by -XImplicitParams.

-XForeignFunctionInterface

Enable foreign function interface.

-XFunctionalDependencies

Enable functional dependencies. Implies -XMultiParamTypeClasses.

-XGADTs

Enable generalised algebraic data types. Implies -XGADTSyntax and -XMonoLocalBinds.

-XGADTSyntax

Enable generalised algebraic data type syntax.

-XGeneralizedNewtypeDeriving

Enable newtype deriving.

-XGenerics

Deprecated, does nothing. No longer enables generic classes. See also GHC’s support for generic programming.

-XImplicitParams

Enable Implicit Parameters. Implies -XFlexibleContexts and -XFlexibleInstances.

-XNoImplicitPrelude

Don’t implicitly import Prelude. Implied by -XRebindableSyntax.

-XImpredicativeTypes

Enable impredicative types. Implies -XRankNTypes.

-XIncoherentInstances

Enable incoherent instances. Implies -XOverlappingInstances.

-XTypeFamilyDependencies

Enable injective type families. Implies -XTypeFamilies.

-XInstanceSigs

Enable instance signatures.

-XInterruptibleFFI

Enable interruptible FFI.

-XKindSignatures

Enable kind signatures. Implied by -XTypeFamilies and -XPolyKinds.

-XLambdaCase

Enable lambda-case expressions.

-XLiberalTypeSynonyms

Enable liberalised type synonyms.

-XMagicHash

Allow # as a postfix modifier on identifiers.

-XMonadComprehensions

Enable monad comprehensions.

-XMonoLocalBinds

Enable do not generalise local bindings. Implied by -XTypeFamilies and -XGADTs.

-XNoMonomorphismRestriction

Disable the monomorphism restriction.

-XMultiParamTypeClasses

Enable multi parameter type classes. Implied by -XFunctionalDependencies.

-XMultiWayIf

Enable multi-way if-expressions.

-XNamedFieldPuns

Enable record puns.

-XNamedWildCards

Enable named wildcards.

-XNegativeLiterals

Enable support for negative literals.

-XNPlusKPatterns

Enable support for n+k patterns. Implied by -XHaskell98.

-XNullaryTypeClasses

Deprecated, does nothing. nullary (no parameter) type classes are now enabled using -XMultiParamTypeClasses.

-XNumDecimals

Enable support for ‘fractional’ integer literals.

-XOverlappingInstances

Enable overlapping instances.

-XOverloadedLabels

Enable overloaded labels.

-XOverloadedLists

Enable overloaded lists.

-XOverloadedStrings

Enable overloaded string literals.

-XPackageImports

Enable package-qualified imports.

-XParallelArrays

Enable parallel arrays. Implies -XParallelListComp.

-XParallelListComp

Enable parallel list comprehensions. Implied by -XParallelArrays.

-XPartialTypeSignatures

Enable partial type signatures.

-XNoPatternGuards

Disable pattern guards. Implied by -XHaskell98.

-XPatternSynonyms

Enable pattern synonyms.

-XPolyKinds

Enable kind polymorphism. Implies -XKindSignatures.

-XPolymorphicComponents

Enable polymorphic components for data constructors. Synonym for -XRankNTypes.

-XPostfixOperators

Enable postfix operators.

-XQuasiQuotes

Enable quasiquotation.

-XRank2Types

Enable rank-2 types. Synonym for -XRankNTypes.

-XRankNTypes

Enable rank-N types. Implied by -XImpredicativeTypes.

-XRebindableSyntax

Employ rebindable syntax. Implies -XNoImplicitPrelude.

-XRecordWildCards

Enable record wildcards. Implies -XDisambiguateRecordFields.

-XRecursiveDo

Enable recursive do (mdo) notation.

-XRoleAnnotations

Enable role annotations.

-XSafe

Enable the Safe Haskell Safe mode.

-XScopedTypeVariables

Enable lexically-scoped type variables.

-XStandaloneDeriving

Enable standalone deriving.

-XStaticPointers

Enable static pointers.

-XStrictData

Enable default strict datatype fields.

-XTemplateHaskell

Enable Template Haskell.

-XTemplateHaskellQuotes

Enable quotation subset of Template Haskell.

-XNoTraditionalRecordSyntax

Disable support for traditional record syntax (as supported by Haskell 98) C {f = x}

-XTransformListComp

Enable generalised list comprehensions.

-XTrustworthy

Enable the Safe Haskell Trustworthy mode.

-XTupleSections

Enable tuple sections.

-XTypeFamilies

Enable type families. Implies -XExplicitNamespaces, -XKindSignatures, and -XMonoLocalBinds.

-XTypeInType

Allow kinds to be used as types, including explicit kind variable quantification, higher-rank kinds, kind synonyms, and kind families. Implies -XDataKinds, -XKindSignatures, and -XPolyKinds.

-XTypeOperators

Enable type operators. Implies -XExplicitNamespaces.

-XTypeSynonymInstances

Enable type synonyms in instance heads. Implied by -XFlexibleInstances.

-XUnboxedTuples

Enable unboxed tuples.

-XUnboxedSums

Enable :ref: unboxed sums <unboxed-sums>.

-XUndecidableInstances

Enable undecidable instances.

-XUnicodeSyntax

Enable unicode syntax.

-XUnliftedFFITypes

Enable unlifted FFI types.

-XUnsafe

Enable Safe Haskell Unsafe mode.

-XViewPatterns

Enable view patterns.

Linking options

-shared

Generate a shared library (as opposed to an executable)

-staticlib

On Darwin/OS X/iOS only, generate a standalone static library (as opposed to an executable). This is the usual way to compile for iOS.

-fPIC

Generate position-independent code (where available)

-fPIE

Generate code for a position-independent executable (where available)

-pie

Instruct the linker to produce a position-independent executable.

-dynload

Selects one of a number of modes for finding shared libraries at runtime.

-framework ⟨name⟩

On Darwin/OS X/iOS only, link in the framework ⟨name⟩. This option corresponds to the -framework option for Apple’s Linker.

-framework-path ⟨dir⟩

On Darwin/OS X/iOS only, add ⟨dir⟩ to the list of directories searched for frameworks. This option corresponds to the -F option for Apple’s Linker.

-l ⟨lib⟩

Link in library ⟨lib⟩

-L ⟨dir⟩

Add ⟨dir⟩ to the list of directories searched for libraries

-main-is ⟨thing⟩

Set main module and function

--mk-dll

DLL-creation mode (Windows only)

-no-hs-main

Don’t assume this program contains main

-rtsopts[=⟨none|some|all⟩]

Control whether the RTS behaviour can be tweaked via command-lineflags and the GHCRTS environment variable. Using none means no RTS flags can be given; some means only a minimum of safe options can be given (the default), and all (or no argument at all) means that all RTS flags are permitted.

-with-rtsopts=⟨opts⟩

Set the default RTS options to ⟨opts⟩.

-no-rtsopts-suggestions

Don’t print RTS suggestions about linking with -rtsopts[=⟨none|some|all⟩].

-no-link

Omit linking

-split-objs

Split objects (for libraries)

-split-sections

Split sections for link-time dead-code stripping

-static

Use static Haskell libraries

-threaded

Use the threaded runtime

-debug

Use the debugging runtime

-ticky

For linking, this simply implies -debug; see Using “ticky-ticky” profiling (for implementors).

-eventlog

Enable runtime event tracing

-fno-gen-manifest

Do not generate a manifest file (Windows only)

-fno-embed-manifest

Do not embed the manifest in the executable (Windows only)

-fno-shared-implib

Don’t generate an import library for a DLL (Windows only)

-dylib-install-name ⟨path⟩

Set the install name (via -install_name passed to Apple’s linker), specifying the full install path of the library file. Any libraries or executables that link with it later will pick up that path as their runtime search location for it. (Darwin/OS X only)

-rdynamic

This instructs the linker to add all symbols, not only used ones, to the dynamic symbol table. Currently Linux and Windows/MinGW32 only. This is equivalent to using -optl -rdynamic on Linux, and -optl -export-all-symbols on Windows.

Miscellaneous options

-j[⟨n⟩]

When compiling with --make, compile ⟨n⟩ modules in parallel.

-fno-hi-version-check

Don’t complain about .hi file mismatches

-fhistory-size

Set simplification history size

-fno-ghci-history

Do not use the load/store the GHCi command history from/to ghci_history.

-fno-ghci-sandbox

Turn off the GHCi sandbox. Means computations are run in the main thread, rather than a forked thread.

-flocal-ghci-history

Use current directory for the GHCi command history file .ghci-history.

Modes of operation

--help,-?

Display help

--interactive

Interactive mode - normally used by just running ghci; see Using GHCi for details.

--make

Build a multi-module Haskell program, automatically figuring out dependencies. Likely to be much easier, and faster, than using make; see Using ghc --make for details.

-e ⟨expr⟩

Evaluate expr; see Expression evaluation mode for details.

--show-iface ⟨file⟩

display the contents of an interface file.

-M

generate dependency information suitable for use in a Makefile; see Dependency generation for details.

--frontend ⟨module⟩

run GHC with the given frontend plugin; see Frontend plugins for details.

--supported-extensions, --supported-languages

display the supported language extensions

--show-options

display the supported command line options

--info

display information about the compiler

--version, -V

display GHC version

--numeric-version

display GHC version (numeric only)

--print-libdir

display GHC library directory

Individual optimizations

-fcall-arity

Enable call-arity optimisation. Implied by -O.

-fcase-merge

Enable case-merging. Implied by -O.

-fcase-folding

Enable constant folding in case expressions. Implied by -O.

-fcmm-elim-common-blocks

Enable Cmm common block elimination. Implied by -O.

-fcmm-sink

Enable Cmm sinking. Implied by -O.

-fcpr-anal

Turn on CPR analysis in the demand analyser. Implied by -O.

-fcse

Enable common sub-expression elimination. Implied by -O.

-fdicts-cheap

Make dictionary-valued expressions seem cheap to the optimiser.

-fdicts-strict

Make dictionaries strict

-fdmd-tx-dict-sel

Use a special demand transformer for dictionary selectors. Always enabled by default.

-fdo-eta-reduction

Enable eta-reduction. Implied by -O.

-fdo-lambda-eta-expansion

Enable lambda eta-expansion. Always enabled by default.

-feager-blackholing

Turn on eager blackholing

-fenable-rewrite-rules

Switch on all rewrite rules (including rules generated by automatic specialisation of overloaded functions). Implied by -O.

-fexcess-precision

Enable excess intermediate precision

-fexpose-all-unfoldings

Expose all unfoldings, even for very large or recursive functions.

-ffloat-in

Turn on the float-in transformation. Implied by -O.

-ffull-laziness

Turn on full laziness (floating bindings outwards). Implied by -O.

-ffun-to-thunk

Allow worker-wrapper to convert a function closure into a thunk if the function does not use any of its arguments. Off by default.

-fignore-asserts

Ignore assertions in the source. Implied by -O.

-fignore-interface-pragmas

Ignore pragmas in interface files. Implied by -O0 only.

-flate-dmd-anal

Run demand analysis again, at the end of the simplification pipeline

-fliberate-case

Turn on the liberate-case transformation. Implied by -O2.

-fliberate-case-threshold=⟨n⟩

default: 2000. Set the size threshold for the liberate-case transformation to ⟨n⟩

-floopification

Turn saturated self-recursive tail-calls into local jumps in the generated assembly. Implied by -O.

-fmax-inline-alloc-size=⟨n⟩

default: 128. Set the maximum size of inline array allocations to ⟨n⟩ bytes (default: 128). GHC will allocate non-pinned arrays of statically known size in the current nursery block if they’re no bigger than ⟨n⟩ bytes, ignoring GC overheap. This value should be quite a bit smaller than the block size (typically: 4096).

-fmax-inline-memcpy-insns=⟨n⟩

default: 32. Inline memcpy calls if they would generate no more than ⟨n⟩ pseudo instructions.

-fmax-inline-memset-insns=⟨n⟩

default: 32. Inline memset calls if they would generate no more than ⟨n⟩ pseudo instructions

-fmax-relevant-binds=⟨n⟩

default: 6. Set the maximum number of bindings to display in type error messages.

-fmax-uncovered-patterns=⟨n⟩

default: 4. Set the maximum number of patterns to display in warnings about non-exhaustive ones.

-fmax-simplifier-iterations=⟨n⟩

default: 4. Set the max iterations for the simplifier.

-fmax-worker-args=⟨n⟩

default: 10. If a worker has that many arguments, none will be unpacked anymore.

-fno-opt-coercion

Turn off the coercion optimiser

-fno-pre-inlining

Turn off pre-inlining

-fno-state-hack

Turn off the “state hack” whereby any lambda with a real-world state token as argument is considered to be single-entry. Hence OK to inline things inside it.

-fomit-interface-pragmas

Don’t generate interface pragmas. Implied by -O0 only.

-fomit-yields

Omit heap checks when no allocation is being performed.

-foptimal-applicative-do

Use a slower but better algorithm for ApplicativeDo

-fpedantic-bottoms

Make GHC be more precise about its treatment of bottom (but see also -fno-state-hack). In particular, GHC will not eta-expand through a case expression.

-fregs-graph

Use the graph colouring register allocator for register allocation in the native code generator. Implied by -O2.

-fregs-iterative

Use the iterative coalescing graph colouring register allocator in the native code generator.

-fsimplifier-phases=⟨n⟩

default: 2. Set the number of phases for the simplifier. Ignored with -O0.

-fsimpl-tick-factor=⟨n⟩

default: 100. Set the percentage factor for simplifier ticks.

-fspec-constr

Turn on the SpecConstr transformation. Implied by -O2.

-fspec-constr-count=⟨n⟩

default: 3.* Set to ⟨n⟩ the maximum number of specialisations that will be created for any one function by the SpecConstr transformation.

-fspec-constr-threshold=⟨n⟩

default: 2000. Set the size threshold for the SpecConstr transformation to ⟨n⟩.

-fspecialise

Turn on specialisation of overloaded functions. Implied by -O.

-fcross-module-specialise

Turn on specialisation of overloaded functions imported from other modules.

-fstatic-argument-transformation

Turn on the static argument transformation.

-fstrictness

Turn on strictness analysis. Implied by -O. Implies -fworker-wrapper

-fstrictness-before=⟨n⟩

Run an additional strictness analysis before simplifier phase ⟨n⟩

-funbox-small-strict-fields

Flatten strict constructor fields with a pointer-sized representation. Implied by -O.

-funbox-strict-fields

Flatten strict constructor fields

-funfolding-creation-threshold=⟨n⟩

default: 750. Tweak unfolding settings.

-funfolding-dict-discount=⟨n⟩

default: 30. Tweak unfolding settings.

-funfolding-fun-discount=⟨n⟩

default: 60. Tweak unfolding settings.

-funfolding-keeness-factor=⟨n⟩

default: 1.5. Tweak unfolding settings.

-funfolding-use-threshold=⟨n⟩

default: 60. Tweak unfolding settings.

-fvectorisation-avoidance

Enable vectorisation avoidance. Always enabled by default.

-fvectorise

Enable vectorisation of nested data parallelism

-fworker-wrapper

Enable the worker-wrapper transformation after a strictness analysis pass. Implied by -O, and by -fstrictness. Disabled by -fno-strictness. Enabling -fworker-wrapper while strictness analysis is disabled (by -fno-strictness) has no effect.

Optimization levels

-O0

Disable optimisations (default)

-O, -O1

Enable level 1 optimisations

-O2

Enable level 2 optimisations

-Odph

Enable level 2 optimisations, set -fmax-simplifier-iterations=20 and -fsimplifier-phases=3.

Package options

-this-unit-id ⟨unit-id⟩

Compile to be part of unit (i.e. package) ⟨unit-id⟩

-package ⟨pkg⟩

Expose package ⟨pkg⟩

-hide-all-packages

Hide all packages by default

-hide-package ⟨pkg⟩

Hide package ⟨pkg⟩

-ignore-package ⟨pkg⟩

Ignore package ⟨pkg⟩

-package-db ⟨file⟩

Add ⟨file⟩ to the package db stack.

-clear-package-db

Clear the package db stack.

-no-global-package-db

Remove the global package db from the stack.

-global-package-db

Add the global package db to the stack.

-no-user-package-db

Remove the user’s package db from the stack.

-user-package-db

Add the user’s package db to the stack.

-no-auto-link-packages

Don’t automatically link in the base and rts packages.

-trust ⟨pkg⟩

Expose package ⟨pkg⟩ and set it to be trusted

-distrust ⟨pkg⟩

Expose package ⟨pkg⟩ and set it to be distrusted

-distrust-all

Distrust all packages by default

-package-env ⟨file⟩|⟨name⟩

Use the specified package environment.

Phases of compilation

-F

Enable the use of a pre-processor (set with -pgmF ⟨cmd⟩)

-E

Stop after preprocessing (.hspp file)

-C

Stop after generating C (.hc file)

-S

Stop after generating assembly (.s file)

-c

Stop after generating object (.o) file

-x ⟨suffix⟩

Override default behaviour for source files

Overriding external programs

-pgmL ⟨cmd⟩

Use ⟨cmd⟩ as the literate pre-processor

-pgmP ⟨cmd⟩

Use ⟨cmd⟩ as the C pre-processor (with -cpp only)

-pgmc ⟨cmd⟩

Use ⟨cmd⟩ as the C compiler

-pgmlo ⟨cmd⟩

Use ⟨cmd⟩ as the LLVM optimiser

-pgmlc ⟨cmd⟩

Use ⟨cmd⟩ as the LLVM compiler

-pgms ⟨cmd⟩

Use ⟨cmd⟩ as the splitter

-pgma ⟨cmd⟩

Use ⟨cmd⟩ as the assembler

-pgml ⟨cmd⟩

Use ⟨cmd⟩ as the linker

-pgmdll ⟨cmd⟩

Use ⟨cmd⟩ as the DLL generator

-pgmF ⟨cmd⟩

Use ⟨cmd⟩ as the pre-processor (with -F only)

-pgmwindres ⟨cmd⟩

Use ⟨cmd⟩ as the program for embedding manifests on Windows.

-pgmlibtool ⟨cmd⟩

Use ⟨cmd⟩ as the command for libtool (with -staticlib only).

Phase-specific options

-optL ⟨option⟩

pass ⟨option⟩ to the literate pre-processor

-optP ⟨option⟩

pass ⟨option⟩ to cpp (with -cpp only)

-optF ⟨option⟩

pass ⟨option⟩ to the custom pre-processor

-optc ⟨option⟩

pass ⟨option⟩ to the C compiler

-optlo ⟨option⟩

pass ⟨option⟩ to the LLVM optimiser

-optlc ⟨option⟩

pass ⟨option⟩ to the LLVM compiler

-opta ⟨option⟩

pass ⟨option⟩ to the assembler

-optl ⟨option⟩

pass ⟨option⟩ to the linker

-optdll ⟨option⟩

pass ⟨option⟩ to the DLL generator

-optwindres ⟨option⟩

pass ⟨option⟩ to windres.

Platform-specific options

-msse2

(x86 only) Use SSE2 for floating-point operations

-msse4.2

(x86 only) Use SSE4.2 for floating-point operations

Compiler plugins

-fplugin=⟨module⟩

Load a plugin exported by a given module

-fplugin-opt=⟨module⟩:⟨args⟩

Give arguments to a plugin module; module must be specified with -fplugin

Profiling

-prof

Turn on profiling

-fprof-auto

Auto-add SCCs to all bindings not marked INLINE

-fprof-auto-top

Auto-add SCCs to all top-level bindings not marked INLINE

-fprof-auto-exported

Auto-add SCCs to all exported bindings not marked INLINE

-fprof-cafs

Auto-add SCCs to all CAFs

-fno-prof-count-entries

Do not collect entry counts

-ticky

Turn on ticky-ticky profiling

Program coverage

-fhpc

Turn on Haskell program coverage instrumentation

-hpcdir ⟨dir⟩

Directory to deposit .mix files during compilation (default is .hpc)

Recompilation checking

-fforce-recomp

Turn off recompilation checking. This is implied by any -ddump-X option when compiling a single file (i.e. when using -c).

Redirecting output

-hcsuf ⟨suffix⟩

set the suffix to use for intermediate C files

-hidir ⟨dir⟩

set directory for interface files

-hisuf ⟨suffix⟩

set the suffix to use for interface files

-o ⟨file⟩

set output filename

-odir ⟨dir⟩

set directory for object files

-ohi ⟨file⟩

set the filename in which to put the interface

-osuf ⟨suffix⟩

set the output file suffix

-stubdir ⟨dir⟩

redirect FFI stub files

-dumpdir ⟨dir⟩

redirect dump files

-outputdir ⟨dir⟩

set output directory

-dyno ⟨file⟩

Set the output filename for dynamic object files (see -dynamic-too)

-dynosuf ⟨suffix⟩

Set the object suffix for dynamic object files (see -dynamic-too)

-dynhisuf ⟨suffix⟩

Set the hi suffix for dynamic object files (see -dynamic-too)

Temporary files

-tmpdir ⟨dir⟩

set the directory for temporary files

Verbosity options

-v

verbose mode (equivalent to -v3)

-v ⟨n⟩

set verbosity level

-fhide-source-paths

hide module source and object paths

-fprint-potential-instances

display all available instances in type error messages

-fprint-explicit-foralls

Print explicit forall quantification in types. See also -XExplicitForAll

-fprint-explicit-kinds

Print explicit kind foralls and kind arguments in types. See also -XKindSignatures

-fprint-explicit-runtime-reps

Print RuntimeRep variables in types which are runtime-representation polymorphic.

-fprint-unicode-syntax

Use unicode syntax when printing expressions, types and kinds. See also -XUnicodeSyntax

-fprint-expanded-synonyms

In type errors, also print type-synonym-expanded types.

-fprint-typechecker-elaboration

Print extra information from typechecker.

-fdiagnostics-color=(always|auto|never)

Use colors in error messages

-f[no-]diagnostics-show-caret

Whether to show snippets of original source code

-ferror-spans

Output full span in error messages

-Rghc-timing

Summarise timing stats for GHC (same as +RTS -tstderr).

-fshow-hole-constraints

Show constraints when reporting typed holes

-fshow-loaded-modules

Show the names of modules that GHCi loaded after a :load command.

Warnings

-W

enable normal warnings

-w

disable all warnings

-Wall

enable almost all warnings (details in Warnings and sanity-checking)

-Wcompat

enable future compatibility warnings (details in Warnings and sanity-checking)

-Werror

make warnings fatal

-Werror=⟨wflag⟩

make a specific warning fatal

-Wwarn

make warnings non-fatal

-Wwarn=⟨wflag⟩

make a specific warning non-fatal

-Wunrecognised-warning-flags

throw a warning when an unreconised -W... flag is encountered on the command line.

-fshow-warning-groups

show which group an emitted warning belongs to.

-fdefer-type-errors

Turn type errors into warnings, deferring the error until runtime. Implies -fdefer-typed-holes and -fdefer-out-of-scope-variables. See also -Wdeferred-type-errors

-fdefer-typed-holes

Convert typed hole errors into warnings, deferring the error until runtime. Implied by -fdefer-type-errors. See also -Wtyped-holes.

-fdefer-out-of-scope-variables

Convert variable out of scope variables errors into warnings. Implied by -fdefer-type-errors. See also -Wdeferred-out-of-scope-variables.

-fhelpful-errors

Make suggestions for mis-spelled names.

-freverse-errors

Display errors in GHC/GHCi sorted by reverse order of source code line numbers.

-fmax-errors

Limit the number of errors displayed in GHC/GHCi.

-Wdeprecated-flags

warn about uses of commandline flags that are deprecated

-Wduplicate-constraints

warn when a constraint appears duplicated in a type signature

-Wduplicate-exports

warn when an entity is exported multiple times

-Whi-shadowing

warn when a .hi file in the current directory shadows a library

-Widentities

warn about uses of Prelude numeric conversions that are probably the identity (and hence could be omitted)

-Wimplicit-prelude

warn when the Prelude is implicitly imported

-Wincomplete-patterns

warn when a pattern match could fail

-Wincomplete-uni-patterns

warn when a pattern match in a lambda expression or pattern binding could fail

-fmax-pmcheck-iterations=⟨n⟩

the iteration limit for the pattern match checker

-Wincomplete-record-updates

warn when a record update could fail

-Wmissing-fields

warn when fields of a record are uninitialised

-Wmissing-import-lists

warn when an import declaration does not explicitly list all thenames brought into scope

-Wmissing-methods

warn when class methods are undefined

-Wmissing-signatures

warn about top-level functions without signatures

-Wmissing-exported-sigs

(deprecated) warn about top-level functions without signatures, only if they are exported. takes precedence over -Wmissing-signatures

-Wmissing-exported-signatures

warn about top-level functions without signatures, only if they are exported. takes precedence over -Wmissing-signatures

-Wmissing-local-sigs

(deprecated) warn about polymorphic local bindings without signatures

-Wmissing-local-signatures

warn about polymorphic local bindings without signatures

-Wmissing-monadfail-instances

warn when a failable pattern is used in a do-block that does not have a MonadFail instance.

-Wsemigroup

warn when a Monoid is not Semigroup, and on non-Semigroup definitions of (<>)?

-Wmissed-specialisations

warn when specialisation of an imported, overloaded function fails.

-Wall-missed-specialisations

warn when specialisation of any overloaded function fails.

-Wmonomorphism-restriction

warn when the Monomorphism Restriction is applied

-Wname-shadowing

warn when names are shadowed

-Wnoncanonical-monad-instances

warn when Applicative or Monad instances have noncanonical definitions of return, pure, (>>), or (*>). See flag description in Warnings and sanity-checking for more details.

-Wnoncanonical-monadfail-instances

warn when Monad or MonadFail instances have noncanonical definitions of fail.See flag description in Warnings and sanity-checking for more details.

-Wnoncanonical-monoid-instances

warn when Semigroup or Monoid instances have noncanonical definitions of (<>) or mappend. See flag description in Warnings and sanity-checking for more details.

-Worphans

warn when the module contains orphan instance declarations or rewrite rules

-Woverlapping-patterns

warn about overlapping patterns

-Wtabs

warn if there are tabs in the source file

-Wtype-defaults

warn when defaulting happens

-Wunrecognised-pragmas

warn about uses of pragmas that GHC doesn’t recognise

-Wunticked-promoted-constructors

warn if promoted constructors are not ticked

-Wunused-binds

warn about bindings that are unused. Alias for -Wunused-top-binds, -Wunused-local-binds and -Wunused-pattern-binds

-Wunused-top-binds

warn about top-level bindings that are unused

-Wunused-local-binds

warn about local bindings that are unused

-Wunused-pattern-binds

warn about pattern match bindings that are unused

-Wunused-imports

warn about unnecessary imports

-Wunused-matches

warn about variables in patterns that aren’t used

-Wunused-foralls

warn about type variables in user-written foralls that are unused

-Wunused-type-variables

warn about variables in type family or data family instances that are unused

-Wunused-do-bind

warn about do bindings that appear to throw away values of types other than ()

-Wwrong-do-bind

warn about do bindings that appear to throw away monadic values that you should have bound instead

-Wunsafe

warn if the module being compiled is regarded to be unsafe. Should be used to check the safety status of modules when using safe inference. Works on all module types, even those using explicit Safe Haskell modes (such as -XTrustworthy) and so can be used to have the compiler check any assumptions made.

-Wsafe

warn if the module being compiled is regarded to be safe. Should be used to check the safety status of modules when using safe inference. Works on all module types, even those using explicit Safe Haskell modes (such as -XTrustworthy) and so can be used to have the compiler check any assumptions made.

-Wtrustworthy-safe

warn if the module being compiled is marked as -XTrustworthy but it could instead be marked as -XSafe, a more informative bound. Can be used to detectonce a Safe Haskell bound can be improved as dependencies are updated.

-Wwarnings-deprecations

warn about uses of functions & types that have warnings or deprecated pragmas

-Wdeprecations

warn about uses of functions & types that have warnings or deprecated pragmas. Alias for -Wwarnings-deprecations

-Wamp

(deprecated) warn on definitions conflicting with the Applicative-Monad Proposal (AMP)

-Wredundant-constraints

Have the compiler warn about redundant constraints in typesignatures.

-Wdeferred-type-errors

Report warnings when deferred type errors are enabled. This option is enabled by default. See -fdefer-type-errors.

-Wtyped-holes

Report warnings when typed hole errors are deferred until runtime. See -fdefer-typed-holes.

-Wdeferred-out-of-scope-variables

Report warnings when variable out-of-scope errors are deferred until runtime. See :ghc-flag:-fdefer-out-of-scope-variables`.

-Wpartial-type-signatures

warn about holes in partial type signatures when -XPartialTypeSignatures is enabled. Not applicable when -XPartialTypesignatures is not enabled, in which case errors are generated for such holes. See Partial Type Signatures.

-Wderiving-typeable

warn when encountering a request to derive an instance of class Typeable. As of GHC 7.10, such declarations are unnecessary and are ignored by the compiler because GHC has a custom solver for discharging this type of constraint.

-Wmissing-home-modules

warn when encountering a home module imported, but not listed on the command line. Useful for cabal to ensure GHC won’t pick up modules, not listed neither in exposed-modules, nor in other-modules.