4.19. Flag reference

4.19. Flag reference
Prev	Chapter 4. Using GHC	Next

This section is a quick-reference for GHC's command-line flags. For each flag, we also list its static/dynamic status (see Section 4.3, “Static, Dynamic, and Mode options”), and the flag's opposite (if available).

4.19.1. Verbosity options

More details in Section 4.6, “Verbosity options”

Flag	Description	Static/Dynamic	Reverse
`-v`	verbose mode (equivalent to `-v3`)	dynamic	-
`-v``n`	set verbosity level	dynamic	-
`-fprint-explicit-foralls`	print explicit `forall` quantification in types	dynamic	-fno-print-explicit-foralls
`-fprint-explicit-kinds`	print explicit kind foralls and kind arguments in types	dynamic	-fno-print-explicit-kinds
`-ferror-spans`	output full span in error messages	dynamic	-
`-H``size`	Set the minimum heap size to `size`	dynamic	-
`-Rghc-timing`	Summarise timing stats for GHC (same as `+RTS -tstderr`)	dynamic	-

4.19.2. Alternative modes of operation

More details in Section 4.5, “Modes of operation”

Flag	Description	Static/Dynamic	Reverse
`--help`,`-?`	Disply help	mode	-
`--interactive`	Interactive mode - normally used by just running ghci; see Chapter 2, Using GHCi for details.	mode	-
`--make`	Build a multi-module Haskell program, automatically figuring out dependencies. Likely to be much easier, and faster, than using make; see Section 4.5.1, “Using ghc `--make`” for details..	mode	-
`-e expr`	Evaluate `expr`; see Section 4.5.2, “Expression evaluation mode” for details.	mode	-
`--show-iface`	Display the contents of an interface file.	mode	-
`-M`	Generate dependency information suitable for use in a `Makefile`; see Section 4.7.12, “Dependency generation” for details.	mode	-
`--supported-extensions`, `--supported-languages`	display the supported language extensions	mode	-
`--show-options`	display the supported command line options	mode	-
`--info`	display information about the compiler	mode	-
`--version, -V`	display GHC version	mode	-
`--numeric-version`	display GHC version (numeric only)	mode	-
`--print-libdir`	display GHC library directory	mode	-

4.19.3. Which phases to run

Section 4.5.3, “Batch compiler mode”

Flag	Description	Static/Dynamic	Reverse
`-E`	Stop after preprocessing (`.hspp` file)	mode	-
`-C`	Stop after generating C (`.hc` file)	mode	-
`-S`	Stop after generating assembly (`.s` file)	mode	-
`-c`	Stop after generating object (`.o`) file	mode	-
`-x` `suffix`	Override default behaviour for source files	dynamic	-

4.19.4. Redirecting output

Section 4.7.4, “Redirecting the compilation output(s)”

Flag	Description	Static/Dynamic	Reverse
`-hcsuf` `suffix`	set the suffix to use for intermediate C files	dynamic	-
`-hidir` `dir`	set directory for interface files	dynamic	-
`-hisuf` `suffix`	set the suffix to use for interface files	dynamic	-
`-o` `filename`	set output filename	dynamic	-
`-odir` `dir`	set directory for object files	dynamic	-
`-ohi` `filename`	set the filename in which to put the interface	dynamic
`-osuf` `suffix`	set the output file suffix	dynamic	-
`-stubdir` `dir`	redirect FFI stub files	dynamic	-
`-dumpdir` `dir`	redirect dump files	dynamic	-
`-outputdir` `dir`	set output directory	dynamic	-

4.19.5. Keeping intermediate files

Section 4.7.5, “Keeping Intermediate Files”

Flag	Description	Static/Dynamic	Reverse
`-keep-hc-file` or `-keep-hc-files`	retain intermediate `.hc` files	dynamic	-
`-keep-llvm-file` or `-keep-llvm-files`	retain intermediate LLVM `.ll` files	dynamic	-
`-keep-s-file` or `-keep-s-files`	retain intermediate `.s` files	dynamic	-
`-keep-tmp-files`	retain all intermediate temporary files	dynamic	-

4.19.6. Temporary files

Section 4.7.6, “Redirecting temporary files”

Flag	Description	Static/Dynamic	Reverse
`-tmpdir`	set the directory for temporary files	dynamic	-

4.19.7. Finding imports

Section 4.7.3, “The search path”

Flag	Description	Static/Dynamic	Reverse
`-i``dir1`:`dir2`:...	add `dir`, `dir2`, etc. to import path	dynamic/`:set`	-
`-i`	Empty the import directory list	dynamic/`:set`	-

4.19.8. Interface file options

Section 4.7.7, “Other options related to interface files”

Flag	Description	Static/Dynamic	Reverse
`-ddump-hi`	Dump the new interface to stdout	dynamic	-
`-ddump-hi-diffs`	Show the differences vs. the old interface	dynamic	-
`-ddump-minimal-imports`	Dump a minimal set of imports	dynamic	-
`--show-iface` `file`	See Section 4.5, “Modes of operation”.

4.19.9. Recompilation checking

Section 4.7.8, “The recompilation checker”

Flag	Description	Static/Dynamic	Reverse
`-fforce-recomp`	Turn off recompilation checking. This is implied by any `-ddump-X` option when compiling a single file (i.e. when using `-c`).	dynamic	`-fno-force-recomp`

4.19.10. Interactive-mode options

Section 2.9, “The .ghci file”

Flag	Description	Static/Dynamic	Reverse
`-ignore-dot-ghci`	Disable reading of `.ghci` files	dynamic	-
`-ghci-script`	Read additional `.ghci` files	dynamic	-
`-fbreak-on-error`	Break on uncaught exceptions and errors	dynamic	`-fno-break-on-error`
`-fbreak-on-exception`	Break on any exception thrown	dynamic	`-fno-break-on-exception`
`-fghci-hist-size=n`	Set the number of entries GHCi keeps for `:history`	dynamic	`(default is 50)`
`-fprint-evld-with-show`	Enable usage of Show instances in `:print`	dynamic	`-fno-print-evld-with-show`
`-fprint-bind-result`	Turn on printing of binding results in GHCi	dynamic	`-fno-print-bind-result`
`-fno-print-bind-contents`	Turn off printing of binding contents in GHCi	dynamic	-
`-fno-implicit-import-qualified`	Turn off implicit qualified import of everything in GHCi	dynamic	-
`-interactive-print`	Select the function to use for printing evaluated expressions in GHCi	dynamic	-

4.19.11. Packages

Section 4.9, “ Packages ”

Flag	Description	Static/Dynamic	Reverse
`-this-package-key` `P`	Compile to be part of package `P`	dynamic	-
`-package` `P`	Expose package `P`	dynamic/`:set`	-
`-hide-all-packages`	Hide all packages by default	dynamic	-
`-hide-package` `name`	Hide package `P`	dynamic/`:set`	-
`-ignore-package` `name`	Ignore package `P`	dynamic/`:set`	-
`-package-db` `file`	Add `file` to the package db stack.	dynamic	-
`-clear-package-db`	Clear the package db stack.	dynamic	-
`-no-global-package-db`	Remove the global package db from the stack.	dynamic	-
`-global-package-db`	Add the global package db to the stack.	dynamic	-
`-no-user-package-db`	Remove the user's package db from the stack.	dynamic	-
`-user-package-db`	Add the user's package db to the stack.	dynamic	-
`-no-auto-link-packages`	Don't automatically link in the base and rts packages.	dynamic	-
`-trust` `P`	Expose package `P` and set it to be trusted	dynamic/`:set`	-
`-distrust` `P`	Expose package `P` and set it to be distrusted	dynamic/`:set`	-
`-distrust-all`	Distrust all packages by default	dynamic/`:set`	-

4.19.12. Language options

Language options can be enabled either by a command-line option -Xblah, or by a {-# LANGUAGE blah #-} pragma in the file itself. See Section 7.1, “Language options”. Some options are enabled using -f* flags.

Flag	Description	Static/Dynamic	Reverse
`-fcontext-stack=``n`	set the limit for type-class context reduction. Default is 100.	dynamic
`-fglasgow-exts`	Deprecated. Enable most language extensions; see Section 7.1, “Language options” for exactly which ones.	dynamic	`-fno-glasgow-exts`
`-firrefutable-tuples`	Make tuple pattern matching irrefutable	dynamic	`-fno-irrefutable-tuples`
`-fpackage-trust`	Enable Safe Haskell trusted package requirement for trustworthy modules.	dynamic	`-`
`-ftype-function-depth=``n`	set the limit for type function reductions. Default is 200.	dynamic
`-XAllowAmbiguousTypes`	Allow the user to write ambiguous types, and the type inference engine to infer them.	dynamic	`-XNoAllowAmbiguousTypes`
`-XArrows`	Enable arrow notation extension	dynamic	`-XNoArrows`
`-XAutoDeriveTypeable`	Automatically derive Typeable instances for every datatype and type class declaration. Implies `-XDeriveDataTypeable`.	dynamic	`-XNoAutoDeriveTypeable`
`-XBangPatterns`	Enable bang patterns.	dynamic	`-XNoBangPatterns`
`-XBinaryLiterals`	Enable support for binary literals.	dynamic	`-XNoBinaryLiterals`
`-XCApiFFI`	Enable the CAPI calling convention.	dynamic	`-XNoCAPIFFI`
`-XConstrainedClassMethods`	Enable constrained class methods.	dynamic	`-XNoConstrainedClassMethods`
`-XConstraintKinds`	Enable a kind of constraints.	dynamic	`-XNoConstraintKinds`
`-XCPP`	Enable the C preprocessor.	dynamic	`-XNoCPP`
`-XDataKinds`	Enable datatype promotion.	dynamic	`-XNoDataKinds`
`-XDefaultSignatures`	Enable default signatures.	dynamic	`-XNoDefaultSignatures`
`-XDeriveAnyClass`	Enable deriving for any class.	dynamic	`-XNoDeriveAnyClass`
`-XDeriveDataTypeable`	Enable deriving for the Data and Typeable classes. Implied by `-XAutoDeriveTypeable`.	dynamic	`-XNoDeriveDataTypeable`
`-XDeriveFunctor`	Enable deriving for the Functor class. Implied by `-XDeriveTraversable`.	dynamic	`-XNoDeriveFunctor`
`-XDeriveFoldable`	Enable deriving for the Foldable class. Implied by `-XDeriveTraversable`.	dynamic	`-XNoDeriveFoldable`
`-XDeriveGeneric`	Enable deriving for the Generic class.	dynamic	`-XNoDeriveGeneric`
`-XDeriveTraversable`	Enable deriving for the Traversable class. Implies `-XDeriveFunctor` and `-XDeriveFoldable`.	dynamic	`-XNoDeriveTraversable`
`-XDisambiguateRecordFields`	Enable record field disambiguation. Implied by `-XRecordWildCards`.	dynamic	`-XNoDisambiguateRecordFields`
`-XEmptyCase`	Allow empty case alternatives.	dynamic	`-XNoEmptyCase`
`-XEmptyDataDecls`	Enable empty data declarations.	dynamic	`-XNoEmptyDataDecls`
`-XExistentialQuantification`	Enable existential quantification.	dynamic	`-XNoExistentialQuantification`
`-XExplicitForAll`	Enable explicit universal quantification. Implied by `-XScopedTypeVariables`, `-XLiberalTypeSynonyms`, `-XRankNTypes` and `-XExistentialQuantification`.	dynamic	`-XNoExplicitForAll`
`-XExplicitNamespaces`	Enable using the keyword `type` to specify the namespace of entries in imports and exports (Section 7.3.26.4, “Explicit namespaces in import/export”). Implied by `-XTypeOperators` and `-XTypeFamilies`.	dynamic	`-XNoExplicitNamespaces`
`-XExtendedDefaultRules`	Use GHCi's extended default rules in a normal module.	dynamic	`-XNoExtendedDefaultRules`
`-XFlexibleContexts`	Enable flexible contexts. Implied by `-XImplicitParams`.	dynamic	`-XNoFlexibleContexts`
`-XFlexibleInstances`	Enable flexible instances. Implies `-XTypeSynonymInstances`. Implied by `-XImplicitParams`.	dynamic	`-XNoFlexibleInstances`
`-XForeignFunctionInterface`	Enable foreign function interface.	dynamic	`-XNoForeignFunctionInterface`
`-XFunctionalDependencies`	Enable functional dependencies. Implies `-XMultiParamTypeClasses`.	dynamic	`-XNoFunctionalDependencies`
`-XGADTs`	Enable generalised algebraic data types. Implies `-XGADTSyntax` and `-XMonoLocalBinds`.	dynamic	`-XNoGADTs`
`-XGADTSyntax`	Enable generalised algebraic data type syntax.	dynamic	`-XNoGADTSyntax`
`-XGeneralizedNewtypeDeriving`	Enable newtype deriving.	dynamic	`-XNoGeneralizedNewtypeDeriving`
`-XGenerics`	Deprecated, does nothing. No longer enables generic classes. See also GHC's support for generic programming.	dynamic	`-XNoGenerics`
`-XImplicitParams`	Enable Implicit Parameters. Implies `-XFlexibleContexts` and `-XFlexibleInstances`.	dynamic	`-XNoImplicitParams`
`-XNoImplicitPrelude`	Don't implicitly `import Prelude`. Implied by `-XRebindableSyntax`.	dynamic	`-XImplicitPrelude`
`-XImpredicativeTypes`	Enable impredicative types. Implies `-XRankNTypes`.	dynamic	`-XNoImpredicativeTypes`
`-XIncoherentInstances`	Enable incoherent instances. Implies `-XOverlappingInstances`.	dynamic	`-XNoIncoherentInstances`
`-XInstanceSigs`	Enable instance signatures.	dynamic	`-XNoInstanceSigs`
`-XInterruptibleFFI`	Enable interruptible FFI.	dynamic	`-XNoInterruptibleFFI`
`-XKindSignatures`	Enable kind signatures. Implied by `-XTypeFamilies` and `-XPolyKinds`.	dynamic	`-XNoKindSignatures`
`-XLambdaCase`	Enable lambda-case expressions.	dynamic	`-XNoLambdaCase`
`-XLiberalTypeSynonyms`	Enable liberalised type synonyms.	dynamic	`-XNoLiberalTypeSynonyms`
`-XMagicHash`	Allow "#" as a postfix modifier on identifiers.	dynamic	`-XNoMagicHash`
`-XMonadComprehensions`	Enable monad comprehensions.	dynamic	`-XNoMonadComprehensions`
`-XMonoLocalBinds`	Enable do not generalise local bindings. Implied by `-XTypeFamilies` and `-XGADTs`.	dynamic	`-XNoMonoLocalBinds`
`-XNoMonomorphismRestriction`	Disable the monomorphism restriction.	dynamic	`-XMonomorphismRestriction`
`-XMultiParamTypeClasses`	Enable multi parameter type classes. Implied by `-XFunctionalDependencies`.	dynamic	`-XNoMultiParamTypeClasses`
`-XMultiWayIf`	Enable multi-way if-expressions.	dynamic	`-XNoMultiWayIf`
`-XNamedFieldPuns`	Enable record puns.	dynamic	`-XNoNamedFieldPuns`
`-XNamedWildcards`	Enable named wildcards.	dynamic	`-XNoNamedWildcards`
`-XNegativeLiterals`	Enable support for negative literals.	dynamic	`-XNoNegativeLiterals`
`-XNoNPlusKPatterns`	Disable support for `n+k` patterns.	dynamic	`-XNPlusKPatterns`
`-XNullaryTypeClasses`	Deprecated, does nothing. nullary (no parameter) type classes are now enabled using `-XMultiParamTypeClasses`.	dynamic	`-XNoNullaryTypeClasses`
`-XNumDecimals`	Enable support for 'fractional' integer literals.	dynamic	`-XNoNumDecimals`
`-XOverlappingInstances`	Enable overlapping instances.	dynamic	`-XNoOverlappingInstances`
`-XOverloadedLists`	Enable overloaded lists.	dynamic	`-XNoOverloadedLists`
`-XOverloadedStrings`	Enable overloaded string literals.	dynamic	`-XNoOverloadedStrings`
`-XPackageImports`	Enable package-qualified imports.	dynamic	`-XNoPackageImports`
`-XParallelArrays`	Enable parallel arrays. Implies `-XParallelListComp`.	dynamic	`-XNoParallelArrays`
`-XParallelListComp`	Enable parallel list comprehensions. Implied by `-XParallelArrays`.	dynamic	`-XNoParallelListComp`
`-XPartialTypeSignatures`	Enable partial type signatures.	dynamic	`-XNoPartialTypeSignatures`
`-XPatternGuards`	Enable pattern guards.	dynamic	`-XNoPatternGuards`
`-XPatternSynonyms`	Enable pattern synonyms.	dynamic	`-XNoPatternSynonyms`
`-XPolyKinds`	Enable kind polymorphism. Implies `-XKindSignatures`.	dynamic	`-XNoPolyKinds`
`-XPolymorphicComponents`	Enable polymorphic components for data constructors.	dynamic, synonym for `-XRankNTypes`	`-XNoPolymorphicComponents`
`-XPostfixOperators`	Enable postfix operators.	dynamic	`-XNoPostfixOperators`
`-XQuasiQuotes`	Enable quasiquotation.	dynamic	`-XNoQuasiQuotes`
`-XRank2Types`	Enable rank-2 types.	dynamic, synonym for `-XRankNTypes`	`-XNoRank2Types`
`-XRankNTypes`	Enable rank-N types. Implied by `-XImpredicativeTypes`.	dynamic	`-XNoRankNTypes`
`-XRebindableSyntax`	Employ rebindable syntax. Implies `-XNoImplicitPrelude`.	dynamic	`-XNoRebindableSyntax`
`-XRecordWildCards`	Enable record wildcards. Implies `-XDisambiguateRecordFields`.	dynamic	`-XNoRecordWildCards`
`-XRecursiveDo`	Enable recursive do (mdo) notation.	dynamic	`-XNoRecursiveDo`
`-XRelaxedPolyRec`	(deprecated) Relaxed checking for mutually-recursive polymorphic functions.	dynamic	`-XNoRelaxedPolyRec`
`-XRoleAnnotations`	Enable role annotations.	dynamic	`-XNoRoleAnnotations`
`-XSafe`	Enable the Safe Haskell Safe mode.	dynamic	`-`
`-XScopedTypeVariables`	Enable lexically-scoped type variables.	dynamic	`-XNoScopedTypeVariables`
`-XStandaloneDeriving`	Enable standalone deriving.	dynamic	`-XNoStandaloneDeriving`
`-XTemplateHaskell`	Enable Template Haskell.	dynamic	`-XNoTemplateHaskell`
`-XNoTraditionalRecordSyntax`	Disable support for traditional record syntax (as supported by Haskell 98) `C {f = x}`	dynamic	`-XTraditionalRecordSyntax`
`-XTransformListComp`	Enable generalised list comprehensions.	dynamic	`-XNoTransformListComp`
`-XTrustworthy`	Enable the Safe Haskell Trustworthy mode.	dynamic	`-`
`-XTupleSections`	Enable tuple sections.	dynamic	`-XNoTupleSections`
`-XTypeFamilies`	Enable type families. Implies `-XExplicitNamespaces`, `-XKindSignatures` and `-XMonoLocalBinds`.	dynamic	`-XNoTypeFamilies`
`-XTypeOperators`	Enable type operators. Implies `-XExplicitNamespaces`.	dynamic	`-XNoTypeOperators`
`-XTypeSynonymInstances`	Enable type synonyms in instance heads. Implied by `-XFlexibleInstances`.	dynamic	`-XNoTypeSynonymInstances`
`-XUnboxedTuples`	Enable unboxed tuples.	dynamic	`-XNoUnboxedTuples`
`-XUndecidableInstances`	Enable undecidable instances.	dynamic	`-XNoUndecidableInstances`
`-XUnicodeSyntax`	Enable unicode syntax.	dynamic	`-XNoUnicodeSyntax`
`-XUnliftedFFITypes`	Enable unlifted FFI types.	dynamic	`-XNoUnliftedFFITypes`
`-XUnsafe`	Enable Safe Haskell Unsafe mode.	dynamic	`-`
`-XViewPatterns`	Enable view patterns.	dynamic	`-XNoViewPatterns`

4.19.13. Warnings

Section 4.8, “Warnings and sanity-checking”

Flag	Description	Static/Dynamic	Reverse
`-W`	enable normal warnings	dynamic	`-w`
`-w`	disable all warnings	dynamic	-
`-Wall`	enable almost all warnings (details in Section 4.8, “Warnings and sanity-checking”)	dynamic	`-w`
`-Werror`	make warnings fatal	dynamic	-Wwarn
`-Wwarn`	make warnings non-fatal	dynamic	-Werror
`-fdefer-type-errors`	Turn type errors into warnings, deferring the error until runtime. Implies `-fdefer-typed-holes`.	dynamic	`-fno-defer-type-errors`
`-fdefer-typed-holes`	Convert typed hole errors into warnings, deferring the error until runtime. Implied by `-fdefer-type-errors`. See also `-fwarn-typed-holes`.	dynamic	`-fno-defer-typed-holes`
`-fhelpful-errors`	Make suggestions for mis-spelled names.	dynamic	`-fno-helpful-errors`
`-fwarn-deprecated-flags`	warn about uses of commandline flags that are deprecated	dynamic	`-fno-warn-deprecated-flags`
`-fwarn-duplicate-constraints`	warn when a constraint appears duplicated in a type signature	dynamic	`-fno-warn-duplicate-constraints`
`-fwarn-duplicate-exports`	warn when an entity is exported multiple times	dynamic	`-fno-warn-duplicate-exports`
`-fwarn-hi-shadowing`	warn when a `.hi` file in the current directory shadows a library	dynamic	`-fno-warn-hi-shadowing`
`-fwarn-identities`	warn about uses of Prelude numeric conversions that are probably the identity (and hence could be omitted)	dynamic	`-fno-warn-identities`
`-fwarn-implicit-prelude`	warn when the Prelude is implicitly imported	dynamic	`-fno-warn-implicit-prelude`
`-fwarn-incomplete-patterns`	warn when a pattern match could fail	dynamic	`-fno-warn-incomplete-patterns`
`-fwarn-incomplete-uni-patterns`	warn when a pattern match in a lambda expression or pattern binding could fail	dynamic	`-fno-warn-incomplete-uni-patterns`
`-fwarn-incomplete-record-updates`	warn when a record update could fail	dynamic	`-fno-warn-incomplete-record-updates`
`-fwarn-lazy-unlifted-bindings`	(deprecated) warn when a pattern binding looks lazy but must be strict	dynamic	`-fno-warn-lazy-unlifted-bindings`
`-fwarn-missing-fields`	warn when fields of a record are uninitialised	dynamic	`-fno-warn-missing-fields`
`-fwarn-missing-import-lists`	warn when an import declaration does not explicitly list all the names brought into scope	dynamic	`-fnowarn-missing-import-lists`
`-fwarn-missing-methods`	warn when class methods are undefined	dynamic	`-fno-warn-missing-methods`
`-fwarn-missing-signatures`	warn about top-level functions without signatures	dynamic	`-fno-warn-missing-signatures`
`-fwarn-missing-exported-sigs`	warn about top-level functions without signatures, only if they are exported. takes precedence over -fwarn-missing-signatures	dynamic	`-fno-warn-missing-exported-sigs`
`-fwarn-missing-local-sigs`	warn about polymorphic local bindings without signatures	dynamic	`-fno-warn-missing-local-sigs`
`-fwarn-monomorphism-restriction`	warn when the Monomorphism Restriction is applied	dynamic	`-fno-warn-monomorphism-restriction`
`-fwarn-name-shadowing`	warn when names are shadowed	dynamic	`-fno-warn-name-shadowing`
`-fwarn-orphans, -fwarn-auto-orphans`	warn when the module contains orphan instance declarations or rewrite rules	dynamic	`-fno-warn-orphans, -fno-warn-auto-orphans`
`-fwarn-overlapping-patterns`	warn about overlapping patterns	dynamic	`-fno-warn-overlapping-patterns`
`-fwarn-tabs`	warn if there are tabs in the source file	dynamic	`-fno-warn-tabs`
`-fwarn-type-defaults`	warn when defaulting happens	dynamic	`-fno-warn-type-defaults`
`-fwarn-unrecognised-pragmas`	warn about uses of pragmas that GHC doesn't recognise	dynamic	`-fno-warn-unrecognised-pragmas`
`-fwarn-unticked-promoted-constructors`	warn if promoted constructors are not ticked	dynamic	`-fno-warn-unticked-promoted-constructors`
`-fwarn-unused-binds`	warn about bindings that are unused	dynamic	`-fno-warn-unused-binds`
`-fwarn-unused-imports`	warn about unnecessary imports	dynamic	`-fno-warn-unused-imports`
`-fwarn-unused-matches`	warn about variables in patterns that aren't used	dynamic	`-fno-warn-unused-matches`
`-fwarn-unused-do-bind`	warn about do bindings that appear to throw away values of types other than `()`	dynamic	`-fno-warn-unused-do-bind`
`-fwarn-wrong-do-bind`	warn about do bindings that appear to throw away monadic values that you should have bound instead	dynamic	`-fno-warn-wrong-do-bind`
`-fwarn-unsafe`	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.	dynamic	`-fno-warn-unsafe`
`-fwarn-safe`	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.	dynamic	`-fno-warn-safe`
`-fwarn-trustworthy-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 detect once a Safe Haskell bound can be improved as dependencies are updated.	dynamic	`-fno-warn-safe`
`-fwarn-warnings-deprecations`	warn about uses of functions & types that have warnings or deprecated pragmas	dynamic	`-fno-warn-warnings-deprecations`
`-fwarn-amp`	(deprecated) warn on definitions conflicting with the Applicative-Monad Proposal (AMP)	dynamic	`-fno-warn-amp`
`-fwarn-typed-holes`	Report warnings when typed hole errors are deferred until runtime. See `-fdefer-typed-holes`.	dynamic	`-fno-warn-typed-holes`
`-fwarn-partial-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 Section 7.15, “Partial Type Signatures”.	dynamic	`-fno-warn-partial-type-signatures`

4.19.14. Optimisation levels

These options are described in more detail in Section 4.10, “Optimisation (code improvement)”

Flag	Description	Static/Dynamic	Reverse
`-O0`	Disable optimisations (default)	dynamic	`-O`
`-O` or `-O1`	Enable level 1 optimisations	dynamic	`-O0`
`-O2`	Enable level 2 optimisations	dynamic	`-O0`
`-Odph`	Enable level 2 optimisations, set `-fmax-simplifier-iterations=20` and `-fsimplifier-phases=3`.	dynamic	-

See Section 4.19.15, “Individual optimisations” for a list of optimisations enabled on level 1 and level 2.

4.19.15. Individual optimisations

These options are described in more detail in Section 4.10.2, “-f*: platform-independent flags”. If a flag is implied by -O then it is also implied by -O2 (unless flag description explicitly says otherwise). If a flag is implied by -O0 only then the flag is not implied by -O and -O2.

Flag	Description	Static/Dynamic	Reverse
`-fcall-arity`	Enable call-arity optimisation. Implied by `-O`.	dynamic	`-fno-call-arity`
`-fcase-merge`	Enable case-merging. Implied by `-O`.	dynamic	`-fno-case-merge`
`-fcmm-elim-common-blocks`	Enable Cmm common block elimination. Implied by `-O`.	dynamic	`-fno-cmm-elim-common-blocks`
`-fcmm-sink`	Enable Cmm sinking. Implied by `-O`.	dynamic	`-fno-cmm-sink`
`-fcpr-off`	Switch off CPR analysis in the demand analyser.	static	-
`-fcse`	Enable common sub-expression elimination. Implied by `-O`.	dynamic	`-fno-cse`
`-fdicts-cheap`	Make dictionary-valued expressions seem cheap to the optimiser.	dynamic	`-fno-dicts-cheap`
`-fdicts-strict`	Make dictionaries strict	dynamic	`-fno-dicts-strict`
`-fdmd-tx-dict-sel`	Use a special demand transformer for dictionary selectors. Always enabled by default.	dynamic	`-fno-dmd-tx-dict-sel`
`-fdo-eta-reduction`	Enable eta-reduction. Implied by `-O`.	dynamic	`-fno-do-eta-reduction`
`-fdo-lambda-eta-expansion`	Enable lambda eta-expansion. Always enabled by default.	dynamic	`-fno-do-lambda-eta-expansion`
`-feager-blackholing`	Turn on eager blackholing	dynamic	-
`-fenable-rewrite-rules`	Switch on all rewrite rules (including rules generated by automatic specialisation of overloaded functions). Implied by `-O`.	dynamic	`-fno-enable-rewrite-rules`
`-fexcess-precision`	Enable excess intermediate precision	dynamic	`-fno-excess-precision`
`-fexpose-all-unfoldings`	Expose all unfoldings, even for very large or recursive functions.	dynamic	`-fno-expose-all-unfoldings`
`-ffloat-in`	Turn on the float-in transformation. Implied by `-O`.	dynamic	`-fno-float-in`
`-ffull-laziness`	Turn on full laziness (floating bindings outwards). Implied by `-O`.	dynamic	`-fno-full-laziness`
`-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.	dynamic	`-fno-fun-to-thunk`
`-fignore-asserts`	Ignore assertions in the source. Implied by `-O`.	dynamic	`-fno-ignore-asserts`
`-fignore-interface-pragmas`	Ignore pragmas in interface files. Implied by `-O0` only.	dynamic	`-fno-ignore-interface-pragmas`
`-flate-dmd-anal`	Run demand analysis again, at the end of the simplification pipeline	dynamic	`-fno-late-dmd-anal`
`-fliberate-case`	Turn on the liberate-case transformation. Implied by `-O2`.	dynamic	-fno-liberate-case
`-fliberate-case-threshold`=`n`	Set the size threshold for the liberate-case transformation to `n` (default: 2000)	dynamis	`-fno-liberate-case-threshold`
`-floopification`	Turn saturated self-recursive tail-calls into local jumps in the generated assembly. Implied by `-O`.	dynamic	`-fno-loopification`
`-fmax-inline-alloc-size`=`n`	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).	dynamic	-
`-fmax-inline-memcpy-insns`=`n`	Inline memcpy calls if they would generate no more than `n` pseudo instructions (default: 32).	dynamic	-
`-fmax-inline-memset-insns`=`n`	Inline memset calls if they would generate no more than `n` pseudo instructions (default: 32).	dynamic	-
`-fmax-relevant-binds=n`	Set the maximum number of bindings to display in type error messages (default 6).	dynamic	`-fno-max-relevant-bindings`
`-fmax-simplifier-iterations=n`	Set the max iterations for the simplifier (default 4).	dynamic	-
`-fmax-worker-args=n`	If a worker has that many arguments, none will be unpacked anymore (default: 10)	dynamic	-
`-fno-opt-coercion`	Turn off the coercion optimiser	static	-
`-fno-pre-inlining`	Turn off pre-inlining	dynamic	-
`-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.	static	-
`-fomit-interface-pragmas`	Don't generate interface pragmas. Implied by `-O0` only.	dynamic	`-fno-omit-interface-pragmas`
`-fomit-yields`	Omit heap checks when no allocation is being performed.	dynamic	`-fno-omit-yields`
`-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.	dynamic	`-fno-pedantic-bottoms`
`-fregs-graph`	Use the graph colouring register allocator for register allocation in the native code generator. Implied by `-O2`.	dynamic	`-fno-regs-graph`
`-fregs-iterative`	Use the iterative coalescing graph colouring register allocator in the native code generator.	dynamic	`-fno-regs-iterative`
`-fsimplifier-phases=n`	Set the number of phases for the simplifier (default 2). Ignored with `-O0`.	dynamic	-
`-fsimpl-tick-factor=n`	Set the percentage factor for simplifier ticks (default 100)	dynamic	-
`-fspec-constr`	Turn on the SpecConstr transformation. Implied by `-O2`.	dynamic	`-fno-spec-constr`
`-fspec-constr-count`=`n`	Set to `n` (default: 3) the maximum number of specialisations that will be created for any one function by the SpecConstr transformation	dynamic	`-fno-spec-constr-count`
`-fspec-constr-threshold`=`n`	Set the size threshold for the SpecConstr transformation to `n` (default: 2000)	dynamic	`-fno-spec-constr-threshold`
`-fspecialise`	Turn on specialisation of overloaded functions. Implied by `-O`.	dynamic	`-fno-specialise`
`-fstatic-argument-transformation`	Turn on the static argument transformation.	dynamic	`-fno-static-argument-transformation`
`-fstrictness`	Turn on strictness analysis. Implied by `-O`.	dynamic	`-fno-strictness`
`-fstrictness-before`=`n`	Run an additional strictness analysis before simplifier phase `n`	dynamic	-
`-funbox-small-strict-fields`	Flatten strict constructor fields with a pointer-sized representation. Implied by `-O`.	dynamic	`-fno-unbox-small-strict-fields`
`-funbox-strict-fields`	Flatten strict constructor fields	dynamic	`-fno-unbox-strict-fields`
`-funfolding-creation-threshold=n`	Tweak unfolding settings. Default: 750	dynamic	-
`-funfolding-dict-discount=n`	Tweak unfolding settings. Default: 30	dynamic	-
`-funfolding-fun-discount=n`	Tweak unfolding settings. Default: 60	dynamic	-
`-funfolding-keeness-factor=n`	Tweak unfolding settings. Default: 1.5	dynamic	-
`-funfolding-use-threshold=n`	Tweak unfolding settings. Default: 60	dynamic	-
`-fvectorisation-avoidance`	Enable vectorisation avoidance. Always enabled by default.	dynamic	`-fno-vectorisation-avoidance`
`-fvectorise`	Enable vectorisation of nested data parallelism	dynamic	`-fno-vectorise`

4.19.16. Profiling options

Chapter 5, Profiling

Flag	Description	Static/Dynamic	Reverse
`-prof`	Turn on profiling	dynamic	-
`-fprof-auto`	Auto-add `SCC`s to all bindings not marked INLINE	dynamic	`-fno-prof-auto`
`-fprof-auto-top`	Auto-add `SCC`s to all top-level bindings not marked INLINE	dynamic	`-fno-prof-auto`
`-fprof-auto-exported`	Auto-add `SCC`s to all exported bindings not marked INLINE	dynamic	`-fno-prof-auto`
`-fprof-cafs`	Auto-add `SCC`s to all CAFs	dynamic	`-fno-prof-cafs`
`-fno-prof-count-entries`	Do not collect entry counts	dynamic	`-fprof-count-entries`
`-ticky`	Turn on ticky-ticky profiling	dynamic	-

4.19.17. Program coverage options

Section 5.7, “Observing Code Coverage”

Flag	Description	Static/Dynamic	Reverse
`-fhpc`	Turn on Haskell program coverage instrumentation	dynamic	`-`
`-hpcdir dir`	Directory to deposit .mix files during compilation (default is .hpc)	dynamic	`-`

4.19.18. Haskell pre-processor options

Section 4.12.4, “Options affecting a Haskell pre-processor”

Flag	Description	Static/Dynamic	Reverse
`-F`	Enable the use of a pre-processor (set with `-pgmF`)	dynamic	-

4.19.19. C pre-processor options

Section 4.12.3, “Options affecting the C pre-processor”

Flag	Description	Static/Dynamic	Reverse
`-cpp`	Run the C pre-processor on Haskell source files	dynamic	-
`-D``symbol`[=`value`]	Define a symbol in the C pre-processor	dynamic	`-U``symbol`
`-U``symbol`	Undefine a symbol in the C pre-processor	dynamic	-
`-I``dir`	Add `dir` to the directory search list for `#include` files	dynamic	-

4.19.20. Code generation options

Section 4.12.5, “Options affecting code generation”

Flag	Description	Static/Dynamic	Reverse
`-fasm`	Use the native code generator	dynamic	-fllvm
`-fllvm`	Compile using the LLVM code generator	dynamic	-fasm
`-fno-code`	Omit code generation	dynamic	-
`-fwrite-interface`	Always write interface files	dynamic	-
`-fbyte-code`	Generate byte-code	dynamic	-
`-fobject-code`	Generate object code	dynamic	-

4.19.21. Linking options

Section 4.12.6, “Options affecting linking”

Flag	Description	Static/Dynamic	Reverse
`-shared`	Generate a shared library (as opposed to an executable)	dynamic	-
`-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.	dynamic	-
`-fPIC`	Generate position-independent code (where available)	dynamic	-
`-dynamic`	Use dynamic Haskell libraries (if available)	dynamic	-
`-dynamic-too`	Build dynamic object files as well as static object files during compilation	dynamic	-
`-dyno`	Set the output path for the dynamically linked objects	dynamic	-
`-dynosuf`	Set the output suffix for dynamic object files	dynamic	-
`-dynload`	Selects one of a number of modes for finding shared libraries at runtime.	dynamic	-
`-framework` `name`	On Darwin/OS X/iOS only, link in the framework `name`. This option corresponds to the `-framework` option for Apple's Linker.	dynamic	-
`-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.	dynamic	-
`-l``lib`	Link in library `lib`	dynamic	-
`-L``dir`	Add `dir` to the list of directories searched for libraries	dynamic	-
`-main-is`	Set main module and function	dynamic	-
`--mk-dll`	DLL-creation mode (Windows only)	dynamic	-
`-no-hs-main`	Don't assume this program contains `main`	dynamic	-
`-rtsopts`, `-rtsopts={none,some,all}`	Control whether the RTS behaviour can be tweaked via command-line flags 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.	dynamic	-
`-with-rtsopts=opts`	Set the default RTS options to `opts`.	dynamic	-
`-no-link`	Omit linking	dynamic	-
`-split-objs`	Split objects (for libraries)	dynamic	-
`-static`	Use static Haskell libraries	dynamic	-
`-threaded`	Use the threaded runtime	dynamic	-
`-debug`	Use the debugging runtime	dynamic	-
`-ticky`	For linking, this simply implies `-debug`; see Section 5.8, “Using “ticky-ticky” profiling (for implementors)”.	dynamic	-
`-eventlog`	Enable runtime event tracing	dynamic	-
`-fno-gen-manifest`	Do not generate a manifest file (Windows only)	dynamic	-
`-fno-embed-manifest`	Do not embed the manifest in the executable (Windows only)	dynamic	-
`-fno-shared-implib`	Don't generate an import library for a DLL (Windows only)	dynamic	-
`-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)	dynamic	-
`-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.	dynamic	-

4.19.22. Plugin options

Section 9.3, “Compiler Plugins”

Flag	Description	Static/Dynamic	Reverse
`-fplugin`=`module`	Load a plugin exported by a given module	dynamic	-
`-fplugin-opt`=`module:args`	Give arguments to a plugin module; module must be specified with `-fplugin`	dynamic	-

4.19.23. Replacing phases

Section 4.12.1, “Replacing the program for one or more phases”

Flag	Description	Static/Dynamic	Reverse
`-pgmL` `cmd`	Use `cmd` as the literate pre-processor	dynamic	-
`-pgmP` `cmd`	Use `cmd` as the C pre-processor (with `-cpp` only)	dynamic	-
`-pgmc` `cmd`	Use `cmd` as the C compiler	dynamic	-
`-pgms` `cmd`	Use `cmd` as the splitter	dynamic	-
`-pgma` `cmd`	Use `cmd` as the assembler	dynamic	-
`-pgml` `cmd`	Use `cmd` as the linker	dynamic	-
`-pgmdll` `cmd`	Use `cmd` as the DLL generator	dynamic	-
`-pgmF` `cmd`	Use `cmd` as the pre-processor (with `-F` only)	dynamic	-
`-pgmwindres` `cmd`	Use `cmd` as the program for embedding manifests on Windows.	dynamic	-
`-pgmlibtool` `cmd`	Use `cmd` as the command for libtool (with `-staticlib` only).	dynamic	-

4.19.24. Forcing options to particular phases

Section 4.12.2, “Forcing options to a particular phase”

Flag	Description	Static/Dynamic	Reverse
`-optL` `option`	pass `option` to the literate pre-processor	dynamic	-
`-optP` `option`	pass `option` to cpp (with `-cpp` only)	dynamic	-
`-optF` `option`	pass `option` to the custom pre-processor	dynamic	-
`-optc` `option`	pass `option` to the C compiler	dynamic	-
`-optlo` `option`	pass `option` to the LLVM optimiser	dynamic	-
`-optlc` `option`	pass `option` to the LLVM compiler	dynamic	-
`-opta` `option`	pass `option` to the assembler	dynamic	-
`-optl` `option`	pass `option` to the linker	dynamic	-
`-optdll` `option`	pass `option` to the DLL generator	dynamic	-
`-optwindres` `option`	pass `option` to `windres`.	dynamic	-

4.19.25. Platform-specific options

Section 4.16, “Platform-specific Flags”

Flag	Description	Static/Dynamic	Reverse
`-msse2`	(x86 only) Use SSE2 for floating point	dynamic	-

4.19.26. Compiler debugging options

Section 4.18, “Debugging the compiler”

Flag	Description	Static/Dynamic	Reverse
`-dcore-lint`	Turn on internal sanity checking	dynamic	-
`-ddump-to-file`	Dump to files instead of stdout	dynamic	-
`-ddump-asm`	Dump assembly	dynamic	-
`-ddump-bcos`	Dump interpreter byte code	dynamic	-
`-ddump-cmm`	Dump C-- output	dynamic	-
`-ddump-core-stats`	Print a one-line summary of the size of the Core program at the end of the optimisation pipeline	dynamic	-
`-ddump-cpranal`	Dump output from CPR analysis	dynamic	-
`-ddump-cse`	Dump CSE output	dynamic	-
`-ddump-deriv`	Dump deriving output	dynamic	-
`-ddump-ds`	Dump desugarer output	dynamic	-
`-ddump-flatC`	Dump “flat” C	dynamic	-
`-ddump-foreign`	Dump `foreign export` stubs	dynamic	-
`-ddump-hpc`	Dump after instrumentation for program coverage	dynamic	-
`-ddump-inlinings`	Dump inlining info	dynamic	-
`-ddump-llvm`	Dump LLVM intermediate code	dynamic	-
`-ddump-occur-anal`	Dump occurrence analysis output	dynamic	-
`-ddump-opt-cmm`	Dump the results of C-- to C-- optimising passes	dynamic	-
`-ddump-parsed`	Dump parse tree	dynamic	-
`-ddump-prep`	Dump prepared core	dynamic	-
`-ddump-rn`	Dump renamer output	dynamic	-
`-ddump-rule-firings`	Dump rule firing info	dynamic	-
`-ddump-rule-rewrites`	Dump detailed rule firing info	dynamic	-
`-ddump-rules`	Dump rules	dynamic	-
`-ddump-vect`	Dump vectoriser input and output	dynamic	-
`-ddump-simpl`	Dump final simplifier output	dynamic	-
`-ddump-simpl-iterations`	Dump output from each simplifier iteration	dynamic	-
`-ddump-spec`	Dump specialiser output	dynamic	-
`-ddump-splices`	Dump TH spliced expressions, and what they evaluate to	dynamic	-
`-ddump-stg`	Dump final STG	dynamic	-
`-ddump-stranal`	Dump strictness analyser output	dynamic	-
`-ddump-strsigs`	Dump strictness signatures	dynamic	-
`-ddump-tc`	Dump typechecker output	dynamic	-
`-ddump-types`	Dump type signatures	dynamic	-
`-ddump-worker-wrapper`	Dump worker-wrapper output	dynamic	-
`-ddump-if-trace`	Trace interface files	dynamic	-
`-ddump-tc-trace`	Trace typechecker	dynamic	-
`-ddump-vt-trace`	Trace vectoriser	dynamic	-
`-ddump-rn-trace`	Trace renamer	dynamic	-
`-ddump-rn-stats`	Renamer stats	dynamic	-
`-ddump-simpl-stats`	Dump simplifier stats	dynamic	-
`-dno-debug-output`	Suppress unsolicited debugging output	static	-
`-dppr-debug`	Turn on debug printing (more verbose)	static	-
`-dppr-user-length`	Set the depth for printing expressions in error msgs	dynamic	-
`-dppr-colsNNN`	Set the width of debugging output. For example `-dppr-cols200`	dynamic	-
`-dppr-case-as-let`	Print single alternative case expressions as strict lets.	dynamic	-
`-dsuppress-all`	In core dumps, suppress everything (except for uniques) that is suppressible.	dynamic	-
`-dsuppress-uniques`	Suppress the printing of uniques in debug output (easier to use diff)	dynamic	-
`-dsuppress-idinfo`	Suppress extended information about identifiers where they are bound	dynamic	-
`-dsuppress-module-prefixes`	Suppress the printing of module qualification prefixes	dynamic	-
`-dsuppress-type-signatures`	Suppress type signatures	dynamic	-
`-dsuppress-type-applications`	Suppress type applications	dynamic	-
`-dsuppress-coercions`	Suppress the printing of coercions in Core dumps to make them shorter	dynamic	-
`-dsource-stats`	Dump haskell source stats	dynamic	-
`-dcmm-lint`	C-- pass sanity checking	dynamic	-
`-dstg-lint`	STG pass sanity checking	dynamic	-
`-dstg-stats`	Dump STG stats	dynamic	-
`-dverbose-core2core`	Show output from each core-to-core pass	dynamic	-
`-dverbose-stg2stg`	Show output from each STG-to-STG pass	dynamic	-
`-dshow-passes`	Print out each pass name as it happens	dynamic	-
`-dfaststring-stats`	Show statistics for fast string usage when finished	dynamic	-
`-frule-check`	Report sites with rules that could have fired but didn't. Takes a string argument.	dynamic	-

4.19.27. Misc compiler options

Flag	Description	Static/Dynamic	Reverse
`-jN`	When compiling with `--make`, compile `N` modules in parallel.	dynamic	-
`-fno-hi-version-check`	Don't complain about `.hi` file mismatches	dynamic	-
`-fhistory-size`	Set simplification history size	dynamic	-
`-fno-ghci-history`	Do not use the load/store the GHCi command history from/to `ghci_history`.	dynamic	-
`-fno-ghci-sandbox`	Turn off the GHCi sandbox. Means computations are run in the main thread, rather than a forked thread.	dynamic	-

Prev	Up	Next
4.18. Debugging the compiler	Home	Chapter 5. Profiling