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ghc - the Glasgow Haskell Compiler

GHC(1) Glasgow Haskell Compiler GHC(1)

NAME

ghc - the Glasgow Haskell Compiler

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 -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 -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 ⟨dir1⟩:⟨dir2⟩:... -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
Interface files
-ddump-hi -ddump-hi-diffs -ddump-minimal-imports --show-iface ⟨file⟩
Keeping intermediate files
-keep-hc-file, -keep-hc-files -keep-llvm-file, -keep-llvm-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 -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 -XNoNPlusKPatterns -XNullaryTypeClasses -XNumDecimals -XOverlappingInstances -XOverloadedLists -XOverloadedStrings -XPackageImports -XParallelArrays -XParallelListComp -XPartialTypeSignatures -XPatternGuards -XPatternSynonyms -XPolyKinds -XPolymorphicComponents -XPostfixOperators -XQuasiQuotes -XRank2Types -XRankNTypes -XRebindableSyntax -XRecordWildCards -XRecursiveDo -XRoleAnnotations -XSafe -XScopedTypeVariables -XStandaloneDeriving -XStrictData -XTemplateHaskell -XTemplateHaskellQuotes -XNoTraditionalRecordSyntax -XTransformListComp -XTrustworthy -XTupleSections -XTypeFamilies -XTypeOperators -XTypeSynonymInstances -XUnboxedTuples -XUndecidableInstances -XUnicodeSyntax -XUnliftedFFITypes -XUnsafe -XViewPatterns
Linking options
-shared -staticlib -fPIC -dynload -framework⟨name⟩ -framework-path⟨name⟩ -l⟨lib⟩ -L⟨dir⟩ -main-is --mk-dll -no-hs-main -rtsopts,-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
-jN -fno-hi-version-check -fhistory-size -fno-ghci-history -fno-ghci-sandbox -freverse-errors
Modes of operation
--help,-? --interactive --make -e expr --show-iface -M --frontend ⟨module⟩ --supported-extensions, --supported-languages --show-options --info --version, -V --numeric-version --print-libdir
Individual optimizations
-fcall-arity -fcase-merge -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-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⟨P⟩ -package⟨P⟩ -hide-all-packages -hide-package⟨name⟩ -ignore-package⟨name⟩ -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⟨P⟩ -distrust⟨P⟩ -distrust-all
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 ⟨filename⟩ -odir ⟨dir⟩ -ohi ⟨filename⟩ -osuf ⟨suffix⟩ -stubdir ⟨dir⟩ -dumpdir ⟨dir⟩ -outputdir ⟨dir⟩ -dyno <filename> -dynosuf <suffix> -dynhisuf <suffix>
Temporary files
-tmpdir ⟨dir⟩
Verbosity options
-v -v⟨n⟩ -fprint-potential-instances -fprint-explicit-foralls -fprint-explicit-kinds -fprint-explicit-runtime-reps -fprint-unicode-syntax -fprint-expanded-synonyms -fprint-typechecker-elaboration -ferror-spans -Rghc-timing
Warnings
-W -w -Wall -Wcompat -Werror -Wwarn -Wunrecognised-warning-flags -fshow-warning-groups -fdefer-type-errors -fdefer-typed-holes -fdefer-out-of-scope-variables -fhelpful-errors -Wdeprecated-flags -Wduplicate-constraints -Wduplicate-exports -Whi-shadowing -Widentities -Wimplicit-prelude -Wincomplete-patterns -Wincomplete-uni-patterns -Wmax-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 -Wamp -Wredundant-constraints -Wdeferred-type-errors -Wtyped-holes -Wdeferred-out-of-scope-variables -Wpartial-type-signatures -Wderiving-typeable

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
Dump 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
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 ⟨dir1⟩:⟨dir2⟩:...
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 ghci-debugger.
-fprint-evld-with-show
Enable usage of Show instances in :print. See breakpoints.
-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
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.

Keeping intermediate files

-keep-hc-file, -keep-hc-files
Retain intermediate .hc files.
-keep-llvm-file, -keep-llvm-files
Retain intermediate LLVM .ll files. Implies -fllvm.
-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 options-language 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.
-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). 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.
-XNoNPlusKPatterns
Disable support for n+k patterns.
-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.
-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.
-XPatternGuards
Enable pattern guards.
-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.
-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.
-XTypeOperators
Enable type operators. Implies -XExplicitNamespaces.
-XTypeSynonymInstances
Enable type synonyms in instance heads. Implied by -XFlexibleInstances.
-XUnboxedTuples
Enable unboxed tuples.
-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)
-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⟨name⟩
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
Set main module and function
--mk-dll
DLL-creation mode (Windows only)
-no-hs-main
Don't assume this program contains main
-rtsopts,-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.
-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 ticky-ticky.
-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

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

Modes of operation

--help,-?
Display help
--interactive
Interactive mode - normally used by just running ghci; see 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 make-mode for details.
-e expr
Evaluate expr; see eval-mode for details.
--show-iface
display the contents of an interface file.
-M
generate dependency information suitable for use in a Makefile; see makefile-dependencies 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.
-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-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⟨P⟩
Compile to be part of unit (i.e. package) ⟨P⟩
-package⟨P⟩
Expose package ⟨P⟩
-hide-all-packages
Hide all packages by default
-hide-package⟨name⟩
Hide package ⟨P⟩
-ignore-package⟨name⟩
Ignore package ⟨P⟩
-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⟨P⟩
Expose package ⟨P⟩ and set it to be trusted
-distrust⟨P⟩
Expose package ⟨P⟩ and set it to be distrusted
-distrust-all
Distrust all packages by default

Phases of compilation

-F
Enable the use of a pre-processor (set with -pgmF)
-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 ⟨filename⟩
set output filename
-odir ⟨dir⟩
set directory for object files
-ohi ⟨filename⟩
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 <filename>
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
-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 -XKindSignature
-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.
-ferror-spans
Output full span in error messages
-Rghc-timing
Summarise timing stats for GHC (same as +RTS -tstderr).

Warnings

-W
enable normal warnings
-w
disable all warnings
-Wall
enable almost all warnings (details in options-sanity)
-Wcompat
enable future compatibility warnings (details in options-sanity)
-Werror
make warnings fatal
-Wwarn
make warnings 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.
-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
-Wmax-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 options-sanity for more details.
-Wnoncanonical-monadfail-instances
warn when Monad or MonadFail instances have noncanonical definitions of fail.See flag description in options-sanity for more details.
-Wnoncanonical-monoid-instances
warn when Semigroup or Monoid instances have noncanonical definitions of (<>) or mappend. See flag description in options-sanity 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
-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 -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.

Copyright 2015. The University Court of the University of Glasgow. All rights reserved.

AUTHOR

The GHC Team 2017, GHC Team
August 29, 2017 8.0.2