Safe Haskell | Safe-Inferred |
---|---|

Language | Haskell2010 |

## Synopsis

- tcMatchTy :: Type -> Type -> Maybe Subst
- tcMatchTyKi :: Type -> Type -> Maybe Subst
- tcMatchTys :: [Type] -> [Type] -> Maybe Subst
- tcMatchTyKis :: [Type] -> [Type] -> Maybe Subst
- tcMatchTyX :: Subst -> Type -> Type -> Maybe Subst
- tcMatchTysX :: Subst -> [Type] -> [Type] -> Maybe Subst
- tcMatchTyKisX :: Subst -> [Type] -> [Type] -> Maybe Subst
- tcMatchTyX_BM :: BindFun -> Subst -> Type -> Type -> Maybe Subst
- ruleMatchTyKiX :: TyCoVarSet -> RnEnv2 -> TvSubstEnv -> Type -> Type -> Maybe TvSubstEnv
- tcUnifyTy :: Type -> Type -> Maybe Subst
- tcUnifyTyKi :: Type -> Type -> Maybe Subst
- tcUnifyTys :: BindFun -> [Type] -> [Type] -> Maybe Subst
- tcUnifyTyKis :: BindFun -> [Type] -> [Type] -> Maybe Subst
- tcUnifyTysFG :: BindFun -> [Type] -> [Type] -> UnifyResult
- tcUnifyTyWithTFs :: Bool -> InScopeSet -> Type -> Type -> Maybe Subst
- type BindFun = TyCoVar -> Type -> BindFlag
- data BindFlag
- matchBindFun :: TyCoVarSet -> BindFun
- alwaysBindFun :: BindFun
- type UnifyResult = UnifyResultM Subst
- data UnifyResultM a
- data MaybeApartReason
- typesCantMatch :: [(Type, Type)] -> Bool
- typesAreApart :: Type -> Type -> Bool
- liftCoMatch :: TyCoVarSet -> Type -> Coercion -> Maybe LiftingContext
- flattenTys :: InScopeSet -> [Type] -> [Type]
- flattenTysX :: InScopeSet -> [Type] -> ([Type], TyVarEnv (TyCon, [Type]))

# Documentation

tcMatchTy :: Type -> Type -> Maybe Subst Source #

`tcMatchTy t1 t2`

produces a substitution (over fvs(t1))
`s`

such that `s(t1)`

equals `t2`

.
The returned substitution might bind coercion variables,
if the variable is an argument to a GADT constructor.

Precondition: typeKind ty1 `eqType`

typeKind ty2

We don't pass in a set of "template variables" to be bound by the match, because tcMatchTy (and similar functions) are always used on top-level types, so we can bind any of the free variables of the LHS. See also Note [tcMatchTy vs tcMatchTyKi]

tcMatchTyKi :: Type -> Type -> Maybe Subst Source #

Like `tcMatchTy`

, but allows the kinds of the types to differ,
and thus matches them as well.
See also Note [tcMatchTy vs tcMatchTyKi]

:: [Type] | Template |

-> [Type] | Target |

-> Maybe Subst | One-shot; in principle the template variables could be free in the target |

Like `tcMatchTy`

but over a list of types.
See also Note [tcMatchTy vs tcMatchTyKi]

Like `tcMatchTyKi`

but over a list of types.
See also Note [tcMatchTy vs tcMatchTyKi]

This is similar to `tcMatchTy`

, but extends a substitution
See also Note [tcMatchTy vs tcMatchTyKi]

Like `tcMatchTys`

, but extending a substitution
See also Note [tcMatchTy vs tcMatchTyKi]

Like `tcMatchTyKis`

, but extending a substitution
See also Note [tcMatchTy vs tcMatchTyKi]

:: TyCoVarSet | template variables |

-> RnEnv2 | |

-> TvSubstEnv | type substitution to extend |

-> Type | Template |

-> Type | Target |

-> Maybe TvSubstEnv |

This one is called from the expression matcher, which already has a MatchEnv in hand

tcUnifyTy :: Type -> Type -> Maybe Subst Source #

Simple unification of two types; all type variables are bindable Precondition: the kinds are already equal

tcUnifyTyKis :: BindFun -> [Type] -> [Type] -> Maybe Subst Source #

Like `tcUnifyTys`

but also unifies the kinds

tcUnifyTysFG :: BindFun -> [Type] -> [Type] -> UnifyResult Source #

`tcUnifyTysFG bind_tv tys1 tys2`

attempts to find a substitution `s`

(whose
domain elements all respond `BindMe`

to `bind_tv`

) such that
`s(tys1)`

and that of `s(tys2)`

are equal, as witnessed by the returned
Coercions. This version requires that the kinds of the types are the same,
if you unify left-to-right.

:: Bool | True = do two-way unification; False = do one-way matching. See end of sec 5.2 from the paper |

-> InScopeSet | |

-> Type | |

-> Type | |

-> Maybe Subst |

Unify two types, treating type family applications as possibly unifying with anything and looking through injective type family applications. Precondition: kinds are the same

type BindFun = TyCoVar -> Type -> BindFlag Source #

Some unification functions are parameterised by a `BindFun`

, which
says whether or not to allow a certain unification to take place.
A `BindFun`

takes the `TyVar`

involved along with the `Type`

it will
potentially be bound to.

It is possible for the variable to actually be a coercion variable
(Note [Matching coercion variables]), but only when one-way matching.
In this case, the `Type`

will be a `CoercionTy`

.

matchBindFun :: TyCoVarSet -> BindFun Source #

Allow binding only for any variable in the set. Variables may be bound to any type. Used when doing simple matching; e.g. can we find a substitution

S = [a :-> t1, b :-> t2] such that S( Maybe (a, b->Int ) = Maybe (Bool, Char -> Int)

alwaysBindFun :: BindFun Source #

Allow the binding of any variable to any type

type UnifyResult = UnifyResultM Subst Source #

data UnifyResultM a Source #

See Note [Unification result]

#### Instances

Applicative UnifyResultM Source # | |

Defined in GHC.Core.Unify pure :: a -> UnifyResultM a Source # (<*>) :: UnifyResultM (a -> b) -> UnifyResultM a -> UnifyResultM b Source # liftA2 :: (a -> b -> c) -> UnifyResultM a -> UnifyResultM b -> UnifyResultM c Source # (*>) :: UnifyResultM a -> UnifyResultM b -> UnifyResultM b Source # (<*) :: UnifyResultM a -> UnifyResultM b -> UnifyResultM a Source # | |

Functor UnifyResultM Source # | |

Defined in GHC.Core.Unify fmap :: (a -> b) -> UnifyResultM a -> UnifyResultM b Source # (<$) :: a -> UnifyResultM b -> UnifyResultM a Source # | |

Monad UnifyResultM Source # | |

Defined in GHC.Core.Unify (>>=) :: UnifyResultM a -> (a -> UnifyResultM b) -> UnifyResultM b Source # (>>) :: UnifyResultM a -> UnifyResultM b -> UnifyResultM b Source # return :: a -> UnifyResultM a Source # | |

Outputable a => Outputable (UnifyResultM a) Source # | |

Defined in GHC.Core.Unify ppr :: UnifyResultM a -> SDoc Source # |

data MaybeApartReason Source #

Why are two types `MaybeApart`

? `MARInfinite`

takes precedence:
This is used (only) in Note [Infinitary substitution in lookup] in GHC.Core.InstEnv
As of Feb 2022, we never differentiate between MARTypeFamily and MARTypeVsConstraint;
it's really only MARInfinite that's interesting here.

MARTypeFamily | matching e.g. F Int ~? Bool |

MARInfinite | matching e.g. a ~? Maybe a |

MARTypeVsConstraint | matching Type ~? Constraint or the arrow types See Note [Type and Constraint are not apart] in GHC.Builtin.Types.Prim |

#### Instances

Semigroup MaybeApartReason Source # | |

Defined in GHC.Core.Unify (<>) :: MaybeApartReason -> MaybeApartReason -> MaybeApartReason Source # sconcat :: NonEmpty MaybeApartReason -> MaybeApartReason Source # stimes :: Integral b => b -> MaybeApartReason -> MaybeApartReason Source # | |

Outputable MaybeApartReason Source # | |

Defined in GHC.Core.Unify ppr :: MaybeApartReason -> SDoc Source # |

typesCantMatch :: [(Type, Type)] -> Bool Source #

Given a list of pairs of types, are any two members of a pair surely apart, even after arbitrary type function evaluation and substitution?

liftCoMatch :: TyCoVarSet -> Type -> Coercion -> Maybe LiftingContext Source #

`liftCoMatch`

is sort of inverse to `liftCoSubst`

. In particular, if
`liftCoMatch vars ty co == Just s`

, then `liftCoSubst s ty == co`

,
where `==`

there means that the result of `liftCoSubst`

has the same
type as the original co; but may be different under the hood.
That is, it matches a type against a coercion of the same
"shape", and returns a lifting substitution which could have been
used to produce the given coercion from the given type.
Note that this function is incomplete -- it might return Nothing
when there does indeed exist a possible lifting context.

This function is incomplete in that it doesn't respect the equality
in `eqType`

. That is, it's possible that this will succeed for t1 and
fail for t2, even when t1 `eqType`

t2. That's because it depends on
there being a very similar structure between the type and the coercion.
This incompleteness shouldn't be all that surprising, especially because
it depends on the structure of the coercion, which is a silly thing to do.

The lifting context produced doesn't have to be exacting in the roles of the mappings. This is because any use of the lifting context will also require a desired role. Thus, this algorithm prefers mapping to nominal coercions where it can do so.

flattenTys :: InScopeSet -> [Type] -> [Type] Source #

flattenTysX :: InScopeSet -> [Type] -> ([Type], TyVarEnv (TyCon, [Type])) Source #