ghc-6.12.3: The GHC APISource codeContentsIndex
Constructing expressions
Taking expressions apart
Properties of expressions
Expression and bindings size
Manipulating data constructors and types
Commonly useful utilites for manipulating the Core language
mkInlineMe :: CoreExpr -> CoreExpr
mkSCC :: CostCentre -> Expr b -> Expr b
mkCoerce :: Coercion -> CoreExpr -> CoreExpr
mkCoerceI :: CoercionI -> CoreExpr -> CoreExpr
bindNonRec :: Id -> CoreExpr -> CoreExpr -> CoreExpr
needsCaseBinding :: Type -> CoreExpr -> Bool
mkAltExpr :: AltCon -> [CoreBndr] -> [Type] -> CoreExpr
mkPiType :: Var -> Type -> Type
mkPiTypes :: [Var] -> Type -> Type
findDefault :: [CoreAlt] -> ([CoreAlt], Maybe CoreExpr)
findAlt :: AltCon -> [CoreAlt] -> Maybe CoreAlt
isDefaultAlt :: CoreAlt -> Bool
mergeAlts :: [CoreAlt] -> [CoreAlt] -> [CoreAlt]
trimConArgs :: AltCon -> [CoreArg] -> [CoreArg]
exprType :: CoreExpr -> Type
coreAltType :: CoreAlt -> Type
coreAltsType :: [CoreAlt] -> Type
exprIsDupable :: CoreExpr -> Bool
exprIsTrivial :: CoreExpr -> Bool
exprIsCheap :: CoreExpr -> Bool
exprIsExpandable :: CoreExpr -> Bool
exprIsHNF :: CoreExpr -> Bool
exprOkForSpeculation :: CoreExpr -> Bool
exprIsBig :: Expr b -> Bool
exprIsConApp_maybe :: CoreExpr -> Maybe (DataCon, [CoreExpr])
exprIsBottom :: CoreExpr -> Bool
rhsIsStatic :: PackageId -> CoreExpr -> Bool
coreBindsSize :: [CoreBind] -> Int
exprSize :: CoreExpr -> Int
hashExpr :: CoreExpr -> Int
cheapEqExpr :: Expr b -> Expr b -> Bool
applyTypeToArgs :: CoreExpr -> Type -> [CoreExpr] -> Type
applyTypeToArg :: Type -> CoreExpr -> Type
dataConOrigInstPat :: [Unique] -> DataCon -> [Type] -> ([TyVar], [CoVar], [Id])
dataConRepInstPat :: [Unique] -> DataCon -> [Type] -> ([TyVar], [CoVar], [Id])
dataConRepFSInstPat :: [FastString] -> [Unique] -> DataCon -> [Type] -> ([TyVar], [CoVar], [Id])
Constructing expressions
mkInlineMe :: CoreExpr -> CoreExprSource
Wraps the given expression in an inlining hint unless the expression is trivial in some sense, so that doing so would usually hurt us
mkSCC :: CostCentre -> Expr b -> Expr bSource
Wraps the given expression in the cost centre unless in a way that maximises their utility to the user
mkCoerce :: Coercion -> CoreExpr -> CoreExprSource
Wrap the given expression in the coercion safely, coalescing nested coercions
mkCoerceI :: CoercionI -> CoreExpr -> CoreExprSource
Wrap the given expression in the coercion, dropping identity coercions and coalescing nested coercions
bindNonRec :: Id -> CoreExpr -> CoreExpr -> CoreExprSource

bindNonRec x r b produces either:

 let x = r in b


 case r of x { _DEFAULT_ -> b }

depending on whether we have to use a case or let binding for the expression (see needsCaseBinding). It's used by the desugarer to avoid building bindings that give Core Lint a heart attack, although actually the simplifier deals with them perfectly well. See also MkCore.mkCoreLet

needsCaseBinding :: Type -> CoreExpr -> BoolSource
Tests whether we have to use a case rather than let binding for this expression as per the invariants of CoreExpr: see CoreSyn
:: AltConCase alternative constructor
-> [CoreBndr]Things bound by the pattern match
-> [Type]The type arguments to the case alternative
-> CoreExpr
This guy constructs the value that the scrutinee must have given that you are in one particular branch of a case
mkPiType :: Var -> Type -> TypeSource
Makes a (->) type or a forall type, depending on whether it is given a type variable or a term variable.
mkPiTypes :: [Var] -> Type -> TypeSource
mkPiType for multiple type or value arguments
Taking expressions apart
findDefault :: [CoreAlt] -> ([CoreAlt], Maybe CoreExpr)Source
Extract the default case alternative
findAlt :: AltCon -> [CoreAlt] -> Maybe CoreAltSource
Find the case alternative corresponding to a particular constructor: panics if no such constructor exists
isDefaultAlt :: CoreAlt -> BoolSource
mergeAlts :: [CoreAlt] -> [CoreAlt] -> [CoreAlt]Source
Merge alternatives preserving order; alternatives in the first argument shadow ones in the second
trimConArgs :: AltCon -> [CoreArg] -> [CoreArg]Source


 case (C a b x y) of
        C b x y -> ...

We want to drop the leading type argument of the scrutinee leaving the arguments to match agains the pattern

Properties of expressions
exprType :: CoreExpr -> TypeSource
Recover the type of a well-typed Core expression. Fails when applied to the actual Type expression as it cannot really be said to have a type
coreAltType :: CoreAlt -> TypeSource
Returns the type of the alternatives right hand side
coreAltsType :: [CoreAlt] -> TypeSource
Returns the type of the first alternative, which should be the same as for all alternatives
exprIsDupable :: CoreExpr -> BoolSource
exprIsTrivial :: CoreExpr -> BoolSource
exprIsCheap :: CoreExpr -> BoolSource
exprIsExpandable :: CoreExpr -> BoolSource
exprIsHNF :: CoreExpr -> BoolSource

This returns true for expressions that are certainly already evaluated to head normal form. This is used to decide whether it's ok to change:

 case x of _ -> e



and to decide whether it's safe to discard a seq. So, it does not treat variables as evaluated, unless they say they are. However, it does treat partial applications and constructor applications as values, even if their arguments are non-trivial, provided the argument type is lifted. For example, both of these are values:

 (:) (f x) (map f xs)
 map (...redex...)

Because seq on such things completes immediately.

For unlifted argument types, we have to be careful:

 C (f x :: Int#)

Suppose f x diverges; then C (f x) is not a value. However this can't happen: see CoreSyn. This invariant states that arguments of unboxed type must be ok-for-speculation (or trivial).

exprOkForSpeculation :: CoreExpr -> BoolSource

exprOkForSpeculation returns True of an expression that is:

  • Safe to evaluate even if normal order eval might not evaluate the expression at all, or
  • Safe not to evaluate even if normal order would do so

Precisely, it returns True iff:

  • The expression guarantees to terminate,
  • soon,
  • without raising an exception,
  • without causing a side effect (e.g. writing a mutable variable)

Note that if exprIsHNF e, then exprOkForSpecuation e. As an example of the considerations in this test, consider:

 let x = case y# +# 1# of { r# -> I# r# }
 in E

being translated to:

 case y# +# 1# of { r# -> 
    let x = I# r#
    in E 

We can only do this if the y + 1 is ok for speculation: it has no side effects, and can't diverge or raise an exception.

exprIsBig :: Expr b -> BoolSource
Returns True of expressions that are too big to be compared by cheapEqExpr
exprIsConApp_maybe :: CoreExpr -> Maybe (DataCon, [CoreExpr])Source
Returns Just (dc, [x1..xn]) if the argument expression is a constructor application of the form dc x1 .. xn
exprIsBottom :: CoreExpr -> BoolSource
True of expressions that are guaranteed to diverge upon execution
rhsIsStatic :: PackageId -> CoreExpr -> BoolSource
This function is called only on *top-level* right-hand sides. Returns True if the RHS can be allocated statically in the output, with no thunks involved at all.
Expression and bindings size
coreBindsSize :: [CoreBind] -> IntSource
exprSize :: CoreExpr -> IntSource
A measure of the size of the expressions, strictly greater than 0 It also forces the expression pretty drastically as a side effect
hashExpr :: CoreExpr -> IntSource

Two expressions that hash to the same Int may be equal (but may not be) Two expressions that hash to the different Ints are definitely unequal.

The emphasis is on a crude, fast hash, rather than on high precision.

But unequal here means "not identical"; two alpha-equivalent expressions may hash to the different Ints.

We must be careful that \x.x and \y.y map to the same hash code, (at least if we want the above invariant to be true).

cheapEqExpr :: Expr b -> Expr b -> BoolSource

A cheap equality test which bales out fast! If it returns True the arguments are definitely equal, otherwise, they may or may not be equal.

See also exprIsBig

Manipulating data constructors and types
applyTypeToArgs :: CoreExpr -> Type -> [CoreExpr] -> TypeSource
A more efficient version of applyTypeToArg when we have several arguments. The first argument is just for debugging, and gives some context
applyTypeToArg :: Type -> CoreExpr -> TypeSource
Determines the type resulting from applying an expression to a function with the given type
dataConOrigInstPat :: [Unique] -> DataCon -> [Type] -> ([TyVar], [CoVar], [Id])Source
dataConRepInstPat :: [Unique] -> DataCon -> [Type] -> ([TyVar], [CoVar], [Id])Source
dataConRepFSInstPat :: [FastString] -> [Unique] -> DataCon -> [Type] -> ([TyVar], [CoVar], [Id])Source
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