ghc-8.2.1: The GHC API

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The IdDetails type

data IdDetails Source #

Identifier Details

The IdDetails of an Id give stable, and necessary, information about the Id.



The Id for a record selector

DataConWorkId DataCon

The Id is for a data constructor worker

DataConWrapId DataCon

The Id is for a data constructor wrapper

ClassOpId Class

The Id is a superclass selector, or class operation of a class

PrimOpId PrimOp

The Id is for a primitive operator

FCallId ForeignCall

The Id is for a foreign call. Type will be simple: no type families, newtypes, etc

TickBoxOpId TickBoxOp

The Id is for a HPC tick box (both traditional and binary)

DFunId Bool

A dictionary function. Bool = True = the class has only one method, so may be implemented with a newtype, so it might be bad to be strict on this dictionary


A coercion variable This only covers un-lifted coercions, of type (t1 ~ t2), not their lifted variants

JoinId JoinArity

An Id for a join point taking n arguments Note [Join points] in CoreSyn

coVarDetails :: IdDetails Source #

Just a synonym for CoVarId. Written separately so it can be exported in the hs-boot file.

type JoinArity = Int Source #

The number of arguments that a join point takes. Unlike the arity of a function, this is a purely syntactic property and is fixed when the join point is created (or converted from a value). Both type and value arguments are counted.

The IdInfo type

data IdInfo Source #

Identifier Information

An IdInfo gives optional information about an Id. If present it never lies, but it may not be present, in which case there is always a conservative assumption which can be made.

Two Ids may have different info even though they have the same Unique (and are hence the same Id); for example, one might lack the properties attached to the other.

Most of the IdInfo gives information about the value, or definition, of the Id, independent of its usage. Exceptions to this are demandInfo, occInfo, oneShotInfo and callArityInfo.

Performance note: when we update IdInfo, we have to reallocate this entire record, so it is a good idea not to let this data structure get too big.

vanillaIdInfo :: IdInfo Source #

Basic IdInfo that carries no useful information whatsoever

noCafIdInfo :: IdInfo Source #

More informative IdInfo we can use when we know the Id has no CAF references

The OneShotInfo type

data OneShotInfo Source #

If the Id is a lambda-bound variable then it may have lambda-bound variable info. Sometimes we know whether the lambda binding this variable is a "one-shot" lambda; that is, whether it is applied at most once.

This information may be useful in optimisation, as computations may safely be floated inside such a lambda without risk of duplicating work.



No information


The lambda is applied at most once.

oneShotInfo :: IdInfo -> OneShotInfo Source #

Info about a lambda-bound variable, if the Id is one

noOneShotInfo :: OneShotInfo Source #

It is always safe to assume that an Id has no lambda-bound variable information

Zapping various forms of Info

zapLamInfo :: IdInfo -> Maybe IdInfo Source #

This is used to remove information on lambda binders that we have setup as part of a lambda group, assuming they will be applied all at once, but turn out to be part of an unsaturated lambda as in e.g:

(\x1. \x2. e) arg1

zapFragileInfo :: IdInfo -> Maybe IdInfo Source #

Zap info that depends on free variables

zapDemandInfo :: IdInfo -> Maybe IdInfo Source #

Remove all demand info on the IdInfo

zapUsageInfo :: IdInfo -> Maybe IdInfo Source #

Remove usage (but not strictness) info on the IdInfo

zapUsageEnvInfo :: IdInfo -> Maybe IdInfo Source #

Remove usage environment info from the strictness signature on the IdInfo

The ArityInfo type

type ArityInfo = Arity Source #

Arity Information

An ArityInfo of n tells us that partial application of this Id to up to n-1 value arguments does essentially no work.

That is not necessarily the same as saying that it has n leading lambdas, because coerces may get in the way.

The arity might increase later in the compilation process, if an extra lambda floats up to the binding site.

unknownArity :: Arity Source #

It is always safe to assume that an Id has an arity of 0

callArityInfo :: IdInfo -> ArityInfo Source #

How this is called. n = all calls have at least n arguments

Demand and strictness Info

demandInfo :: IdInfo -> Demand Source #

ID demand information

Unfolding Info

unfoldingInfo :: IdInfo -> Unfolding Source #

The Ids unfolding

The InlinePragInfo type

type InlinePragInfo = InlinePragma Source #

Inline Pragma Information

Tells when the inlining is active. When it is active the thing may be inlined, depending on how big it is.

If there was an INLINE pragma, then as a separate matter, the RHS will have been made to look small with a Core inline Note

The default InlinePragInfo is AlwaysActive, so the info serves entirely as a way to inhibit inlining until we want it

inlinePragInfo :: IdInfo -> InlinePragma Source #

Any inline pragma atached to the Id

The OccInfo type

data OccInfo Source #

identifier Occurrence Information



There are many occurrences, or unknown occurrences


Marks unused variables. Sometimes useful for lambda and case-bound variables.


Occurs exactly once (per branch), not inside a rule


This identifier breaks a loop of mutually recursive functions. The field marks whether it is only a loop breaker due to a reference in a rule


occInfo :: IdInfo -> OccInfo Source #

How the Id occurs in the program

type InsideLam = Bool Source #

Inside Lambda

The RuleInfo type

data RuleInfo Source #

Rule Information

Records the specializations of this Id that we know about in the form of rewrite CoreRules that target them


RuleInfo [CoreRule] DVarSet 

emptyRuleInfo :: RuleInfo Source #

Assume that no specilizations exist: always safe

ruleInfoFreeVars :: RuleInfo -> DVarSet Source #

Retrieve the locally-defined free variables of both the left and right hand sides of the specialization rules

setRuleInfoHead :: Name -> RuleInfo -> RuleInfo Source #

Change the name of the function the rule is keyed on on all of the CoreRules

ruleInfo :: IdInfo -> RuleInfo Source #

Specialisations of the Ids function which exist See Note [Specialisations and RULES in IdInfo]

The CAFInfo type

data CafInfo Source #

Constant applicative form Information

Records whether an Id makes Constant Applicative Form references



Indicates that the Id is for either:

  1. A function or static constructor that refers to one or more CAFs, or
  2. A real live CAF

A function or static constructor that refers to no CAFs.

cafInfo :: IdInfo -> CafInfo Source #

Id CAF info

Tick-box Info

data TickBoxOp Source #

Tick box for Hpc-style coverage


TickBox Module !TickBoxId 

Levity info

levityInfo :: IdInfo -> LevityInfo Source #

when applied, will this Id ever have a levity-polymorphic type?

setNeverLevPoly :: HasDebugCallStack => IdInfo -> Type -> IdInfo infixl 1 Source #

Marks an IdInfo describing an Id that is never levity polymorphic (even when applied). The Type is only there for checking that it's really never levity polymorphic