ghc-7.10.3: The GHC API

Safe HaskellNone




Types for the per-module compiler


compilation state

data HscEnv Source

Hscenv is like Session, except that some of the fields are immutable. An HscEnv is used to compile a single module from plain Haskell source code (after preprocessing) to either C, assembly or C--. Things like the module graph don't change during a single compilation.

Historical note: "hsc" used to be the name of the compiler binary, when there was a separate driver and compiler. To compile a single module, the driver would invoke hsc on the source code... so nowadays we think of hsc as the layer of the compiler that deals with compiling a single module.




hsc_dflags :: DynFlags

The dynamic flag settings

hsc_targets :: [Target]

The targets (or roots) of the current session

hsc_mod_graph :: ModuleGraph

The module graph of the current session

hsc_IC :: InteractiveContext

The context for evaluating interactive statements

hsc_HPT :: HomePackageTable

The home package table describes already-compiled home-package modules, excluding the module we are compiling right now. (In one-shot mode the current module is the only home-package module, so hsc_HPT is empty. All other modules count as "external-package" modules. However, even in GHCi mode, hi-boot interfaces are demand-loaded into the external-package table.)

hsc_HPT is not mutable because we only demand-load external packages; the home package is eagerly loaded, module by module, by the compilation manager.

The HPT may contain modules compiled earlier by --make but not actually below the current module in the dependency graph.

(This changes a previous invariant: changed Jan 05.)

hsc_EPS :: !(IORef ExternalPackageState)

Information about the currently loaded external packages. This is mutable because packages will be demand-loaded during a compilation run as required.

hsc_NC :: !(IORef NameCache)

As with hsc_EPS, this is side-effected by compiling to reflect sucking in interface files. They cache the state of external interface files, in effect.

hsc_FC :: !(IORef FinderCache)

The cached result of performing finding in the file system

hsc_MLC :: !(IORef ModLocationCache)

This caches the location of modules, so we don't have to search the filesystem multiple times. See also hsc_FC.

hsc_type_env_var :: Maybe (Module, IORef TypeEnv)

Used for one-shot compilation only, to initialise the IfGblEnv. See tcg_type_env_var for TcGblEnv

hscEPS :: HscEnv -> IO ExternalPackageState Source

Retrieve the ExternalPackageState cache.

type FinderCache = ModuleNameEnv FindResult Source

The FinderCache maps home module names to the result of searching for that module. It records the results of searching for modules along the search path. On :load, we flush the entire contents of this cache.

Although the FinderCache range is FindResult for convenience, in fact it will only ever contain Found or NotFound entries.

data FindResult Source

The result of searching for an imported module.


Found ModLocation Module

The module was found

NoPackage PackageKey

The requested package was not found

FoundMultiple [(Module, ModuleOrigin)]

_Error_: both in multiple packages


Not found

type ModLocationCache = ModuleEnv ModLocation Source

Cache that remembers where we found a particular module. Contains both home modules and package modules. On :load, only home modules are purged from this cache.

data Target Source

A compilation target.

A target may be supplied with the actual text of the module. If so, use this instead of the file contents (this is for use in an IDE where the file hasn't been saved by the user yet).




targetId :: TargetId

module or filename

targetAllowObjCode :: Bool

object code allowed?

targetContents :: Maybe (StringBuffer, UTCTime)

in-memory text buffer?


data TargetId Source


TargetModule ModuleName

A module name: search for the file

TargetFile FilePath (Maybe Phase)

A filename: preprocess & parse it to find the module name. If specified, the Phase indicates how to compile this file (which phase to start from). Nothing indicates the starting phase should be determined from the suffix of the filename.

type ModuleGraph = [ModSummary] Source

A ModuleGraph contains all the nodes from the home package (only). There will be a node for each source module, plus a node for each hi-boot module.

The graph is not necessarily stored in topologically-sorted order. Use topSortModuleGraph and flattenSCC to achieve this.

data HscStatus Source

Status of a compilation to hard-code

Hsc monad

runHsc :: HscEnv -> Hsc a -> IO a Source

Information about modules

data ModDetails Source

The ModDetails is essentially a cache for information in the ModIface for home modules only. Information relating to packages will be loaded into global environments in ExternalPackageState.




md_exports :: [AvailInfo]
md_types :: !TypeEnv

Local type environment for this particular module Includes Ids, TyCons, PatSyns

md_insts :: ![ClsInst]

DFunIds for the instances in this module

md_fam_insts :: ![FamInst]
md_rules :: ![CoreRule]

Domain may include Ids from other modules

md_anns :: ![Annotation]

Annotations present in this module: currently they only annotate things also declared in this module

md_vect_info :: !VectInfo

Module vectorisation information

emptyModDetails :: ModDetails Source

Constructs an empty ModDetails

data ModGuts Source

A ModGuts is carried through the compiler, accumulating stuff as it goes There is only one ModGuts at any time, the one for the module being compiled right now. Once it is compiled, a ModIface and ModDetails are extracted and the ModGuts is discarded.




mg_module :: !Module

Module being compiled

mg_boot :: IsBootInterface

Whether it's an hs-boot module

mg_exports :: ![AvailInfo]

What it exports

mg_deps :: !Dependencies

What it depends on, directly or otherwise

mg_dir_imps :: !ImportedMods

Directly-imported modules; used to generate initialisation code

mg_used_names :: !NameSet

What the module needed (used in mkIface)

mg_used_th :: !Bool

Did we run a TH splice?

mg_rdr_env :: !GlobalRdrEnv

Top-level lexical environment

mg_fix_env :: !FixityEnv

Fixities declared in this module. Used for creating interface files.

mg_tcs :: ![TyCon]

TyCons declared in this module (includes TyCons for classes)

mg_insts :: ![ClsInst]

Class instances declared in this module

mg_fam_insts :: ![FamInst]

Family instances declared in this module

mg_patsyns :: ![PatSyn]

Pattern synonyms declared in this module

mg_rules :: ![CoreRule]

Before the core pipeline starts, contains See Note [Overall plumbing for rules] in Rules.lhs

mg_binds :: !CoreProgram

Bindings for this module

mg_foreign :: !ForeignStubs

Foreign exports declared in this module

mg_warns :: !Warnings

Warnings declared in the module

mg_anns :: [Annotation]

Annotations declared in this module

mg_hpc_info :: !HpcInfo

Coverage tick boxes in the module

mg_modBreaks :: !ModBreaks

Breakpoints for the module

mg_vect_decls :: ![CoreVect]

Vectorisation declarations in this module (produced by desugarer & consumed by vectoriser)

mg_vect_info :: !VectInfo

Pool of vectorised declarations in the module

mg_inst_env :: InstEnv

Class instance environment from home-package modules (including this one); c.f. tcg_inst_env

mg_fam_inst_env :: FamInstEnv

Type-family instance environment for home-package modules (including this one); c.f. tcg_fam_inst_env

mg_safe_haskell :: SafeHaskellMode

Safe Haskell mode

mg_trust_pkg :: Bool

Do we need to trust our own package for Safe Haskell? See Note [RnNames . Trust Own Package]

mg_dependent_files :: [FilePath]

dependencies from addDependentFile

data CgGuts Source

A restricted form of ModGuts for code generation purposes




cg_module :: !Module

Module being compiled

cg_tycons :: [TyCon]

Algebraic data types (including ones that started life as classes); generate constructors and info tables. Includes newtypes, just for the benefit of External Core

cg_binds :: CoreProgram

The tidied main bindings, including previously-implicit bindings for record and class selectors, and data constructor wrappers. But *not* data constructor workers; reason: we we regard them as part of the code-gen of tycons

cg_foreign :: !ForeignStubs

Foreign export stubs

cg_dep_pkgs :: ![PackageKey]

Dependent packages, used to generate #includes for C code gen

cg_hpc_info :: !HpcInfo

Program coverage tick box information

cg_modBreaks :: !ModBreaks

Module breakpoints

data ForeignStubs Source

Foreign export stubs



We don't have any stubs

ForeignStubs SDoc SDoc

There are some stubs. Parameters:

1) Header file prototypes for "foreign exported" functions

2) C stubs to use when calling "foreign exported" functions

type ImportedMods = ModuleEnv [ImportedModsVal] Source

Records the modules directly imported by a module for extracting e.g. usage information

data ModSummary Source

A single node in a ModuleGraph. The nodes of the module graph are one of:

  • A regular Haskell source module
  • A hi-boot source module
  • An external-core source module




ms_mod :: Module

Identity of the module

ms_hsc_src :: HscSource

The module source either plain Haskell, hs-boot or external core

ms_location :: ModLocation

Location of the various files belonging to the module

ms_hs_date :: UTCTime

Timestamp of source file

ms_obj_date :: Maybe UTCTime

Timestamp of object, if we have one

ms_iface_date :: Maybe UTCTime

Timestamp of hi file, if we *only* are typechecking (it is Nothing otherwise. See Note [Recompilation checking when typechecking only] and #9243

ms_srcimps :: [Located (ImportDecl RdrName)]

Source imports of the module

ms_textual_imps :: [Located (ImportDecl RdrName)]

Non-source imports of the module from the module *text*

ms_hspp_file :: FilePath

Filename of preprocessed source file

ms_hspp_opts :: DynFlags

Cached flags from OPTIONS, INCLUDE and LANGUAGE pragmas in the modules source code

ms_hspp_buf :: Maybe StringBuffer

The actual preprocessed source, if we have it

isBootSummary :: ModSummary -> Bool Source

Did this ModSummary originate from a hs-boot file?

data SourceModified Source

Indicates whether a given module's source has been modified since it was last compiled.



the source has been modified


the source has not been modified. Compilation may or may not be necessary, depending on whether any dependencies have changed since we last compiled.


the source has not been modified, and furthermore all of its (transitive) dependencies are up to date; it definitely does not need to be recompiled. This is important for two reasons: (a) we can omit the version check in checkOldIface, and (b) if the module used TH splices we don't need to force recompilation.

Information about the module being compiled

State relating to modules in this package

type HomePackageTable = ModuleNameEnv HomeModInfo Source

Helps us find information about modules in the home package

data HomeModInfo Source

Information about modules in the package being compiled




hm_iface :: !ModIface

The basic loaded interface file: every loaded module has one of these, even if it is imported from another package

hm_details :: !ModDetails

Extra information that has been created from the ModIface for the module, typically during typechecking

hm_linkable :: !(Maybe Linkable)

The actual artifact we would like to link to access things in this module.

hm_linkable might be Nothing:

  1. If this is an .hs-boot module
  2. Temporarily during compilation if we pruned away the old linkable because it was out of date.

After a complete compilation (load), all hm_linkable fields in the HomePackageTable will be Just.

When re-linking a module (HscNoRecomp), we construct the HomeModInfo by building a new ModDetails from the old ModIface (only).

emptyHomePackageTable :: HomePackageTable Source

Constructs an empty HomePackageTable

hptInstances :: HscEnv -> (ModuleName -> Bool) -> ([ClsInst], [FamInst]) Source

Find all the instance declarations (of classes and families) from the Home Package Table filtered by the provided predicate function. Used in tcRnImports, to select the instances that are in the transitive closure of imports from the currently compiled module.

hptRules :: HscEnv -> [(ModuleName, IsBootInterface)] -> [CoreRule] Source

Get rules from modules "below" this one (in the dependency sense)

hptVectInfo :: HscEnv -> VectInfo Source

Get the combined VectInfo of all modules in the home package table. In contrast to instances and rules, we don't care whether the modules are "below" us in the dependency sense. The VectInfo of those modules not "below" us does not affect the compilation of the current module.

State relating to known packages

data ExternalPackageState Source

Information about other packages that we have slurped in by reading their interface files




eps_is_boot :: !(ModuleNameEnv (ModuleName, IsBootInterface))

In OneShot mode (only), home-package modules accumulate in the external package state, and are sucked in lazily. For these home-pkg modules (only) we need to record which are boot modules. We set this field after loading all the explicitly-imported interfaces, but before doing anything else

The ModuleName part is not necessary, but it's useful for debug prints, and it's convenient because this field comes direct from imp_dep_mods

eps_PIT :: !PackageIfaceTable

The ModIfaces for modules in external packages whose interfaces we have opened. The declarations in these interface files are held in the eps_decls, eps_inst_env, eps_fam_inst_env and eps_rules fields of this record, not in the mi_decls fields of the interface we have sucked in.

What is in the PIT is:

  • The Module
  • Fingerprint info
  • Its exports
  • Fixities
  • Deprecations and warnings
eps_PTE :: !PackageTypeEnv

Result of typechecking all the external package interface files we have sucked in. The domain of the mapping is external-package modules

eps_inst_env :: !PackageInstEnv

The total InstEnv accumulated from all the external-package modules

eps_fam_inst_env :: !PackageFamInstEnv

The total FamInstEnv accumulated from all the external-package modules

eps_rule_base :: !PackageRuleBase

The total RuleEnv accumulated from all the external-package modules

eps_vect_info :: !PackageVectInfo

The total VectInfo accumulated from all the external-package modules

eps_ann_env :: !PackageAnnEnv

The total AnnEnv accumulated from all the external-package modules

eps_mod_fam_inst_env :: !(ModuleEnv FamInstEnv)

The family instances accumulated from external packages, keyed off the module that declared them

eps_stats :: !EpsStats

Stastics about what was loaded from external packages

data EpsStats Source

Accumulated statistics about what we are putting into the ExternalPackageState. "In" means stuff that is just read from interface files, "Out" means actually sucked in and type-checked

addEpsInStats :: EpsStats -> Int -> Int -> Int -> EpsStats Source

Add stats for one newly-read interface

type PackageIfaceTable = ModuleEnv ModIface Source

Helps us find information about modules in the imported packages

emptyPackageIfaceTable :: PackageIfaceTable Source

Constructs an empty PackageIfaceTable

lookupIfaceByModule :: DynFlags -> HomePackageTable -> PackageIfaceTable -> Module -> Maybe ModIface Source

Find the ModIface for a Module, searching in both the loaded home and external package module information

emptyModIface :: Module -> ModIface Source

Constructs an empty ModIface


data MetaRequest Source

The supported metaprogramming result types

data MetaResult Source

data constructors not exported to ensure correct result type


prepareAnnotations :: HscEnv -> Maybe ModGuts -> IO AnnEnv Source

Deal with gathering annotations in from all possible places and combining them into a single AnnEnv

Interactive context

data InteractiveContext Source

Interactive context, recording information about the state of the context in which statements are executed in a GHC session.




ic_dflags :: DynFlags

The DynFlags used to evaluate interative expressions and statements.

ic_mod_index :: Int

Each GHCi stmt or declaration brings some new things into scope. We give them names like interactive:Ghci9.T, where the ic_index is the '9'. The ic_mod_index is incremented whenever we add something to ic_tythings See Note [The interactive package]

ic_imports :: [InteractiveImport]

The GHCi top-level scope (ic_rn_gbl_env) is extended with these imports

This field is only stored here so that the client can retrieve it with GHC.getContext. GHC itself doesn't use it, but does reset it to empty sometimes (such as before a GHC.load). The context is set with GHC.setContext.

ic_tythings :: [TyThing]

TyThings defined by the user, in reverse order of definition (ie most recent at the front) See Note [ic_tythings]

ic_rn_gbl_env :: GlobalRdrEnv

The cached GlobalRdrEnv, built by setContext and updated regularly It contains everything in scope at the command line, including everything in ic_tythings

ic_instances :: ([ClsInst], [FamInst])

All instances and family instances created during this session. These are grabbed en masse after each update to be sure that proper overlapping is retained. That is, rather than re-check the overlapping each time we update the context, we just take the results from the instance code that already does that.

ic_fix_env :: FixityEnv

Fixities declared in let statements

ic_default :: Maybe [Type]

The current default types, set by a 'default' declaration

ic_resume :: [Resume]

The stack of breakpoint contexts

ic_monad :: Name

The monad that GHCi is executing in

ic_int_print :: Name

The function that is used for printing results of expressions in ghci and -e mode.

ic_cwd :: Maybe FilePath

emptyInteractiveContext :: DynFlags -> InteractiveContext Source

Constructs an empty InteractiveContext.

icPrintUnqual :: DynFlags -> InteractiveContext -> PrintUnqualified Source

Get the PrintUnqualified function based on the flags and this InteractiveContext

icInScopeTTs :: InteractiveContext -> [TyThing] Source

This function returns the list of visible TyThings (useful for e.g. showBindings)

icExtendGblRdrEnv :: GlobalRdrEnv -> [TyThing] -> GlobalRdrEnv Source

Add TyThings to the GlobalRdrEnv, earlier ones in the list shadowing later ones, and shadowing existing entries in the GlobalRdrEnv.

extendInteractiveContext :: InteractiveContext -> [Id] -> [TyCon] -> [ClsInst] -> [FamInst] -> Maybe [Type] -> [PatSyn] -> InteractiveContext Source

extendInteractiveContext is called with new TyThings recently defined to update the InteractiveContext to include them. Ids are easily removed when shadowed, but Classes and TyCons are not. Some work could be done to determine whether they are entirely shadowed, but as you could still have references to them (e.g. instances for classes or values of the type for TyCons), it's not clear whether removing them is even the appropriate behavior.

data InteractiveImport Source


IIDecl (ImportDecl RdrName)

Bring the exports of a particular module (filtered by an import decl) into scope

IIModule ModuleName

Bring into scope the entire top-level envt of of this module, including the things imported into it.

mkPrintUnqualified :: DynFlags -> GlobalRdrEnv -> PrintUnqualified Source

Creates some functions that work out the best ways to format names for the user according to a set of heuristics.

mkQualPackage :: DynFlags -> QueryQualifyPackage Source

Creates a function for formatting packages based on two heuristics: (1) don't qualify if the package in question is "main", and (2) only qualify with a package key if the package ID would be ambiguous.

mkQualModule :: DynFlags -> QueryQualifyModule Source

Creates a function for formatting modules based on two heuristics: (1) if the module is the current module, don't qualify, and (2) if there is only one exposed package which exports this module, don't qualify.

pkgQual :: DynFlags -> PrintUnqualified Source

A function which only qualifies package names if necessary; but qualifies all other identifiers.


data ModIface Source

A ModIface plus a ModDetails summarises everything we know about a compiled module. The ModIface is the stuff *before* linking, and can be written out to an interface file. The 'ModDetails is after linking and can be completely recovered from just the ModIface.

When we read an interface file, we also construct a ModIface from it, except that we explicitly make the mi_decls and a few other fields empty; as when reading we consolidate the declarations etc. into a number of indexed maps and environments in the ExternalPackageState.




mi_module :: !Module

Name of the module we are for

mi_sig_of :: !(Maybe Module)

Are we a sig of another mod?

mi_iface_hash :: !Fingerprint

Hash of the whole interface

mi_mod_hash :: !Fingerprint

Hash of the ABI only

mi_flag_hash :: !Fingerprint

Hash of the important flags used when compiling this module

mi_orphan :: !WhetherHasOrphans

Whether this module has orphans

mi_finsts :: !WhetherHasFamInst

Whether this module has family instances

mi_boot :: !IsBootInterface

Read from an hi-boot file?

mi_deps :: Dependencies

The dependencies of the module. This is consulted for directly-imported modules, but not for anything else (hence lazy)

mi_usages :: [Usage]

Usages; kept sorted so that it's easy to decide whether to write a new iface file (changing usages doesn't affect the hash of this module) NOT STRICT! we read this field lazily from the interface file It is *only* consulted by the recompilation checker

mi_exports :: ![IfaceExport]

Exports Kept sorted by (mod,occ), to make version comparisons easier Records the modules that are the declaration points for things exported by this module, and the OccNames of those things

mi_exp_hash :: !Fingerprint

Hash of export list

mi_used_th :: !Bool

Module required TH splices when it was compiled. This disables recompilation avoidance (see #481).

mi_fixities :: [(OccName, Fixity)]

Fixities NOT STRICT! we read this field lazily from the interface file

mi_warns :: Warnings

Warnings NOT STRICT! we read this field lazily from the interface file

mi_anns :: [IfaceAnnotation]

Annotations NOT STRICT! we read this field lazily from the interface file

mi_decls :: [(Fingerprint, IfaceDecl)]

Type, class and variable declarations The hash of an Id changes if its fixity or deprecations change (as well as its type of course) Ditto data constructors, class operations, except that the hash of the parent class/tycon changes

mi_globals :: !(Maybe GlobalRdrEnv)

Binds all the things defined at the top level in the original source code for this module. which is NOT the same as mi_exports, nor mi_decls (which may contains declarations for things not actually defined by the user). Used for GHCi and for inspecting the contents of modules via the GHC API only.

(We need the source file to figure out the top-level environment, if we didn't compile this module from source then this field contains Nothing).

Strictly speaking this field should live in the HomeModInfo, but that leads to more plumbing.

mi_insts :: [IfaceClsInst]

Sorted class instance

mi_fam_insts :: [IfaceFamInst]

Sorted family instances

mi_rules :: [IfaceRule]

Sorted rules

mi_orphan_hash :: !Fingerprint

Hash for orphan rules, class and family instances, and vectorise pragmas combined

mi_vect_info :: !IfaceVectInfo

Vectorisation information

mi_warn_fn :: Name -> Maybe WarningTxt

Cached lookup for mi_warns

mi_fix_fn :: OccName -> Fixity

Cached lookup for mi_fixities

mi_hash_fn :: OccName -> Maybe (OccName, Fingerprint)

Cached lookup for mi_decls. The Nothing in mi_hash_fn means that the thing isn't in decls. It's useful to know that when seeing if we are up to date wrt. the old interface. The OccName is the parent of the name, if it has one.

mi_hpc :: !AnyHpcUsage

True if this program uses Hpc at any point in the program.

mi_trust :: !IfaceTrustInfo

Safe Haskell Trust information for this module.

mi_trust_pkg :: !Bool

Do we require the package this module resides in be trusted to trust this module? This is used for the situation where a module is Safe (so doesn't require the package be trusted itself) but imports some trustworthy modules from its own package (which does require its own package be trusted). See Note [RnNames . Trust Own Package]


mkIfaceWarnCache :: Warnings -> Name -> Maybe WarningTxt Source

Constructs the cache for the mi_warn_fn field of a ModIface

mkIfaceHashCache :: [(Fingerprint, IfaceDecl)] -> OccName -> Maybe (OccName, Fingerprint) Source

Constructs cache for the mi_hash_fn field of a ModIface

mkIfaceFixCache :: [(OccName, Fixity)] -> OccName -> Fixity Source

Creates cached lookup for the mi_fix_fn field of ModIface


type FixityEnv = NameEnv FixItem Source

Fixity environment mapping names to their fixities

data FixItem Source

Fixity information for an Name. We keep the OccName in the range so that we can generate an interface from it


FixItem OccName Fixity 


TyThings and type environments

data TyThing Source

A typecheckable-thing, essentially anything that has a name

tyThingAvailInfo :: TyThing -> AvailInfo Source

The Names that a TyThing should bring into scope. Used to build the GlobalRdrEnv for the InteractiveContext.

tyThingTyCon :: TyThing -> TyCon Source

Get the TyCon from a TyThing if it is a type constructor thing. Panics otherwise

tyThingDataCon :: TyThing -> DataCon Source

Get the DataCon from a TyThing if it is a data constructor thing. Panics otherwise

tyThingId :: TyThing -> Id Source

Get the Id from a TyThing if it is a id *or* data constructor thing. Panics otherwise

tyThingCoAxiom :: TyThing -> CoAxiom Branched Source

Get the CoAxiom from a TyThing if it is a coercion axiom thing. Panics otherwise

tyThingParent_maybe :: TyThing -> Maybe TyThing Source

tyThingParent_maybe x returns (Just p) when pprTyThingInContext sould print a declaration for p (albeit with some "..." in it) when asked to show x It returns the *immediate* parent. So a datacon returns its tycon but the tycon could be the associated type of a class, so it in turn might have a parent.

implicitTyThings :: TyThing -> [TyThing] Source

Determine the TyThings brought into scope by another TyThing other than itself. For example, Id's don't have any implicit TyThings as they just bring themselves into scope, but classes bring their dictionary datatype, type constructor and some selector functions into scope, just for a start!

isImplicitTyThing :: TyThing -> Bool Source

Returns True if there should be no interface-file declaration for this thing on its own: either it is built-in, or it is part of some other declaration, or it is generated implicitly by some other declaration.

type TypeEnv = NameEnv TyThing Source

A map from Names to TyThings, constructed by typechecking local declarations or interface files

lookupType :: DynFlags -> HomePackageTable -> PackageTypeEnv -> Name -> Maybe TyThing Source

Find the TyThing for the given Name by using all the resources at our disposal: the compiled modules in the HomePackageTable and the compiled modules in other packages that live in PackageTypeEnv. Note that this does NOT look up the TyThing in the module being compiled: you have to do that yourself, if desired

lookupTypeHscEnv :: HscEnv -> Name -> IO (Maybe TyThing) Source

As lookupType, but with a marginally easier-to-use interface if you have a HscEnv


class Monad m => MonadThings m where Source

Class that abstracts out the common ability of the monads in GHC to lookup a TyThing in the monadic environment by Name. Provides a number of related convenience functions for accessing particular kinds of TyThing

Minimal complete definition



Information on imports and exports

type WhetherHasOrphans = Bool Source

Records whether a module has orphans. An "orphan" is one of:

  • An instance declaration in a module other than the definition module for one of the type constructors or classes in the instance head
  • A transformation rule in a module other than the one defining the function in the head of the rule
  • A vectorisation pragma

type IsBootInterface = Bool Source

Did this module originate from a *-boot file?

data Usage Source

Records modules for which changes may force recompilation of this module See wiki:

This differs from Dependencies. A module X may be in the dep_mods of this module (via an import chain) but if we don't use anything from X it won't appear in our Usage



Module from another package


usg_mod :: Module

External package module depended on

usg_mod_hash :: Fingerprint

Cached module fingerprint

usg_safe :: IsSafeImport

Was this module imported as a safe import


Module from the current package | A file upon which the module depends, e.g. a CPP #include, or using TH's addDependentFile


usg_mod_name :: ModuleName

Name of the module

usg_mod_hash :: Fingerprint

Cached module fingerprint

usg_entities :: [(OccName, Fingerprint)]

Entities we depend on, sorted by occurrence name and fingerprinted. NB: usages are for parent names only, e.g. type constructors but not the associated data constructors.

usg_exports :: Maybe Fingerprint

Fingerprint for the export list of this module, if we directly imported it (and hence we depend on its export list)

usg_safe :: IsSafeImport

Was this module imported as a safe import



usg_file_path :: FilePath

External file dependency. From a CPP #include or TH addDependentFile. Should be absolute.

usg_file_hash :: Fingerprint

Fingerprint of the file contents.


data Dependencies Source

Dependency information about ALL modules and packages below this one in the import hierarchy.

Invariant: the dependencies of a module M never includes M.

Invariant: none of the lists contain duplicates.




dep_mods :: [(ModuleName, IsBootInterface)]

All home-package modules transitively below this one I.e. modules that this one imports, or that are in the dep_mods of those directly-imported modules

dep_pkgs :: [(PackageKey, Bool)]

All packages transitively below this module I.e. packages to which this module's direct imports belong, or that are in the dep_pkgs of those modules The bool indicates if the package is required to be trusted when the module is imported as a safe import (Safe Haskell). See Note [RnNames . Tracking Trust Transitively]

dep_orphs :: [Module]

Transitive closure of orphan modules (whether home or external pkg).

(Possible optimization: don't include family instance orphans as they are anyway included in dep_finsts. But then be careful about code which relies on dep_orphs having the complete list!)

dep_finsts :: [Module]

Modules that contain family instances (whether the instances are from the home or an external package)

data NameCache Source

The NameCache makes sure that there is just one Unique assigned for each original name; i.e. (module-name, occ-name) pair and provides something of a lookup mechanism for those names.




nsUniqs :: !UniqSupply

Supply of uniques

nsNames :: !OrigNameCache

Ensures that one original name gets one unique

type OrigNameCache = ModuleEnv (OccEnv Name) Source

Per-module cache of original OccNames given Names

type IfaceExport = AvailInfo Source

The original names declared of a certain module that are exported


data Warnings Source

Warning information for a module



Nothing deprecated

WarnAll WarningTxt

Whole module deprecated

WarnSome [(OccName, WarningTxt)]

Some specific things deprecated

Linker stuff

data Linkable Source

Information we can use to dynamically link modules into the compiler




linkableTime :: UTCTime

Time at which this linkable was built (i.e. when the bytecodes were produced, or the mod date on the files)

linkableModule :: Module

The linkable module itself

linkableUnlinked :: [Unlinked]

Those files and chunks of code we have yet to link.

INVARIANT: A valid linkable always has at least one Unlinked item. If this list is empty, the Linkable represents a fake linkable, which is generated in HscNothing mode to avoid recompiling modules.

ToDo: Do items get removed from this list when they get linked?


data Unlinked Source

Objects which have yet to be linked by the compiler


DotO FilePath

An object file (.o)

DotA FilePath

Static archive file (.a)

DotDLL FilePath

Dynamically linked library file (.so, .dll, .dylib)

BCOs CompiledByteCode ModBreaks

A byte-code object, lives only in memory


isObject :: Unlinked -> Bool Source

Is this an actual file on disk we can link in somehow?

nameOfObject :: Unlinked -> FilePath Source

Retrieve the filename of the linkable if possible. Panic if it is a byte-code object

isInterpretable :: Unlinked -> Bool Source

Is this a bytecode linkable with no file on disk?

byteCodeOfObject :: Unlinked -> CompiledByteCode Source

Retrieve the compiled byte-code if possible. Panic if it is a file-based linkable

Program coverage

data HpcInfo Source

Information about a modules use of Haskell Program Coverage




hpcUsed :: AnyHpcUsage

Is hpc used anywhere on the module *tree*?

isHpcUsed :: HpcInfo -> AnyHpcUsage Source

Find out if HPC is used by this module or any of the modules it depends upon

type AnyHpcUsage = Bool Source

This is used to signal if one of my imports used HPC instrumentation even if there is no module-local HPC usage


data ModBreaks Source

All the information about the breakpoints for a given module




modBreaks_flags :: BreakArray

The array of flags, one per breakpoint, indicating which breakpoints are enabled.

modBreaks_locs :: !(Array BreakIndex SrcSpan)

An array giving the source span of each breakpoint.

modBreaks_vars :: !(Array BreakIndex [OccName])

An array giving the names of the free variables at each breakpoint.

modBreaks_decls :: !(Array BreakIndex [String])

An array giving the names of the declarations enclosing each breakpoint.

type BreakIndex = Int Source

Breakpoint index

emptyModBreaks :: ModBreaks Source

Construct an empty ModBreaks

Vectorisation information

data VectInfo Source

Vectorisation information for ModGuts, ModDetails and ExternalPackageState; see also documentation at GlobalEnv.

NB: The following tables may also include Vars, TyCons and DataCons from imported modules, which have been subsequently vectorised in the current module.




vectInfoVar :: VarEnv (Var, Var)

(f, f_v) keyed on f

vectInfoTyCon :: NameEnv (TyCon, TyCon)

(T, T_v) keyed on T

vectInfoDataCon :: NameEnv (DataCon, DataCon)

(C, C_v) keyed on C

vectInfoParallelVars :: VarSet

set of parallel variables

vectInfoParallelTyCons :: NameSet

set of parallel type constructors


data IfaceVectInfo Source

Vectorisation information for ModIface; i.e, the vectorisation information propagated across module boundaries.

NB: The field ifaceVectInfoVar explicitly contains the workers of data constructors as well as class selectors — i.e., their mappings are not implicitly generated from the data types. Moreover, whether the worker of a data constructor is in ifaceVectInfoVar determines whether that data constructor was vectorised (or is part of an abstractly vectorised type constructor).




ifaceVectInfoVar :: [Name]

All variables in here have a vectorised variant

ifaceVectInfoTyCon :: [Name]

All TyCons in here have a vectorised variant; the name of the vectorised variant and those of its data constructors are determined by mkVectTyConOcc and mkVectDataConOcc; the names of the isomorphisms are determined by mkVectIsoOcc

ifaceVectInfoTyConReuse :: [Name]

The vectorised form of all the TyCons in here coincides with the unconverted form; the name of the isomorphisms is determined by mkVectIsoOcc

ifaceVectInfoParallelVars :: [Name]
ifaceVectInfoParallelTyCons :: [Name]

Safe Haskell information

data IfaceTrustInfo Source

Safe Haskell information for ModIface Simply a wrapper around SafeHaskellMode to sepperate iface and flags

type IsSafeImport = Bool Source

Is an import a safe import?

result of the parser

data HsParsedModule Source




hpm_module :: Located (HsModule RdrName)
hpm_src_files :: [FilePath]

extra source files (e.g. from #includes). The lexer collects these from '# file line' pragmas, which the C preprocessor leaves behind. These files and their timestamps are stored in the .hi file, so that we can force recompilation if any of them change (#3589)

hpm_annotations :: ApiAnns

Compilation errors and warnings

data SourceError Source

A source error is an error that is caused by one or more errors in the source code. A SourceError is thrown by many functions in the compilation pipeline. Inside GHC these errors are merely printed via log_action, but API clients may treat them differently, for example, insert them into a list box. If you want the default behaviour, use the idiom:

handleSourceError printExceptionAndWarnings $ do
  ... api calls that may fail ...

The SourceErrors error messages can be accessed via srcErrorMessages. This list may be empty if the compiler failed due to -Werror (Opt_WarnIsError).

See printExceptionAndWarnings for more information on what to take care of when writing a custom error handler.

data GhcApiError Source

An error thrown if the GHC API is used in an incorrect fashion.

handleSourceError Source


:: ExceptionMonad m 
=> (SourceError -> m a)

exception handler

-> m a

action to perform

-> m a 

Perform the given action and call the exception handler if the action throws a SourceError. See SourceError for more information.

printOrThrowWarnings :: DynFlags -> Bag WarnMsg -> IO () Source

Given a bag of warnings, turn them into an exception if -Werror is enabled, or print them out otherwise.