Commit 1411eaf1 authored by's avatar
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Note [TyBinder] in TyCoRep

parent bd7ab668
......@@ -196,7 +196,7 @@ data Type
Type -- ^ A Π type.
-- This includes arrow types, constructed with
-- @ForAllTy (Anon ...)@.
-- @ForAllTy (Anon ...)@. See also Note [TyBinder].
| LitTy TyLit -- ^ Type literals are similar to type constructors.
......@@ -225,6 +225,7 @@ data TyLit
-- | A 'TyBinder' represents an argument to a function. TyBinders can be dependent
-- ('Named') or nondependent ('Anon'). They may also be visible or not.
-- See also Note [TyBinder]
data TyBinder
= Named TyVar VisibilityFlag
| Anon Type -- visibility is determined by the type (Constraint vs. *)
......@@ -264,6 +265,20 @@ type KindOrType = Type -- See Note [Arguments to type constructors]
type Kind = Type
Note [TyBinder]
This represents the type of binders -- that is, the type of an argument
to a Pi-type. GHC Core currently supports two different Pi-types:
a non-dependent function, written with ->, and a dependent compile-time-only
polytype, written with forall. Both Pi-types classify terms/types that
take an argument. In other words, if `x` is either a function or a polytype,
`x arg` makes sense (for an appropriate `arg`). It is thus often convenient
to group Pi-types together. This is ForAllTy.
The two constructors for TyBinder sort out the two different possibilities.
`Named` builds a polytype, while `Anon` builds an ordinary function.
(ForAllTy (Anon arg) res used to be called FunTy arg res.)
Note [The kind invariant]
The kinds
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