Documentation

Type variable that might be a metavariable

Create a new flexi ty var with a specific name

Create a tyvar that can be a lifted or unlifted type. Returns alpha :: TYPE kappa, where both alpha and kappa are fresh

Emits a new Wanted. Deals with both equalities and non-equalities.

Emits a new equality constraint

Creates a new EvVar and immediately emits it as a Wanted. No equality predicates here.

Creates an EvBindsVar incapable of holding any bindings. It still tracks covar usages (see comments on ebv_tcvs in GHC.Tc.Types.Evidence), thus must be made monadically

Emit a new wanted expression hole

Put a value in a coercion hole

Is a coercion hole filled in?

Retrieve the contents of a coercion hole. Panics if the hole is unfilled

Retrieve the contents of a coercion hole, if it is filled

Check that a coercion is appropriate for filling a hole. (The hole itself is needed only for printing.) Always returns the checked coercion, but this return value is necessary so that the input coercion is forced only when the output is forced.

Create a new Implication with as many sensible defaults for its fields as possible. Note that the ic_tclvl, ic_binds, and ic_info fields do not have sensible defaults, so they are initialized with lazy thunks that will panic if forced, so one should take care to initialize these fields after creation.

This is monadic to look up the TcLclEnv, which is used to initialize ic_env, and to set the -Winaccessible-code flag. See Note [Avoid -Winaccessible-code when deriving] in GHC.Tc.TyCl.Instance.

An expected type to check against during type-checking. See Note [ExpType] in GHC.Tc.Utils.TcMType, where you'll also find manipulators.

Make an ExpType suitable for checking.

Infer a type using a fresh ExpType See also Note [ExpType] in GHC.Tc.Utils.TcMType

Extract a type out of an ExpType. Otherwise, panics.

Extract a type out of an ExpType, if one exists. But one should always exist. Unless you're quite sure you know what you're doing.

Same as readExpType, but for Scaled ExpTypes

Extracts the expected type if there is one, or generates a new TauTv if there isn't.

Returns the expected type when in checking mode.

Returns the expected type when in checking mode. Panics if in inference mode.

Gathers free variables to use as quantification candidates (in quantifyTyVars). This might output the same var in both sets, if it's used in both a type and a kind. The variables to quantify must have a TcLevel strictly greater than the ambient level. (See Wrinkle in Note [Naughty quantification candidates]) See Note [CandidatesQTvs determinism and order] See Note [Dependent type variables]

Like candidateQTyVarsOfType, but consider every free variable to be dependent. This is appropriate when generalizing a *kind*, instead of a type. (That way, -XNoPolyKinds will default the variables to Type.)

Like candidateQTyVarsOfType, but over a list of types The variables to quantify must have a TcLevel strictly greater than the ambient level. (See Wrinkle in Note [Naughty quantification candidates])

According to the rules around representation polymorphism (see https://gitlab.haskell.org/ghc/ghc/wikis/no-sub-kinds), no binder can have a representation-polymorphic type. This check ensures that we respect this rule. It is a bit regrettable that this error occurs in zonking, after which we should have reported all errors. But it's hard to see where else to do it, because this can be discovered only after all solving is done. And, perhaps most importantly, this isn't really a compositional property of a type system, so it's not a terrible surprise that the check has to go in an awkward spot.