GHC.Types.RepType

Gets rid of the stuff that prevents us from understanding the runtime representation of a type. Including: 1. Casts 2. Newtypes 3. Foralls 4. Synonyms But not type/data families, because we don't have the envs to hand.

True if the type has zero width.

Discovers the primitive representation of a Type. Returns a list of PrimRep: it's a list because of the possibility of no runtime representation (void) or multiple (unboxed tuple/sum) See also Note [Getting from RuntimeRep to PrimRep]

Like typePrimRep, but assumes that there is at most one PrimRep output; an empty list of PrimReps becomes a VoidRep. This assumption holds after unarise, see Note [Post-unarisation invariants]. Before unarise it may or may not hold. See also Note [RuntimeRep and PrimRep] and Note [VoidRep]

Take a type of kind RuntimeRep and extract the list of PrimRep that it encodes. See also Note [Getting from RuntimeRep to PrimRep]. The [PrimRep] is the final runtime representation after unarisation.

A PrimRep is an abstraction of a non-void type. (Use PrimRepOrVoidRep if you want void types too.) It contains information that the code generator needs in order to pass arguments, return results, and store values of this type. See also Note [RuntimeRep and PrimRep] in GHC.Types.RepType and Note [VoidRep] in GHC.Types.RepType.

Convert a PrimRep to a Type of kind RuntimeRep

Convert a PrimRep back to a Type. Used only in the unariser to give types to fresh Ids. Really, only the type's representation matters. See also Note [RuntimeRep and PrimRep]

Count the arity of a function post-unarisation, including zero-width arguments.

The post-unarisation arity may be larger than the arity of the original function type. See Note [Unarisation].

Give the demands on the arguments of a Core constructor application (Con dc args) at runtime. Assumes the constructor is not levity polymorphic. For example unboxed tuples won't work.

Find the runtime representation of a TyCon. Defined here to avoid module loops. Returns a list of the register shapes necessary. See also Note [Getting from RuntimeRep to PrimRep]

Take a type of kind RuntimeRep and extract the list of PrimRep that it encodes. See also Note [Getting from RuntimeRep to PrimRep]. The [PrimRep] is the final runtime representation after unarisation.

Returns Nothing if rep can't be determined. Eg. levity polymorphic types.

Take a kind (of shape `TYPE rr` or `CONSTRAINT rr`) and produce the PrimReps of values of types of this kind. See also Note [Getting from RuntimeRep to PrimRep] Returns Nothing if rep can't be determined. Eg. levity polymorphic types.

Discovers the primitive representation of a Type. Returns a list of PrimRep: it's a list because of the possibility of no runtime representation (void) or multiple (unboxed tuple/sum) See also Note [Getting from RuntimeRep to PrimRep] Returns Nothing if rep can't be determined. Eg. levity polymorphic types.

Given the arguments of a sum type constructor application, return the unboxed sum rep type.

E.g.

(# Int# | Maybe Int | (# Int#, Float# #) #)

We call `ubxSumRepType [ [IntRep], [LiftedRep], [IntRep, FloatRep] ]`, which returns [WordSlot, PtrSlot, WordSlot, FloatSlot]

INVARIANT: Result slots are sorted (via Ord SlotTy), except that at the head of the list we have the slot for the tag.

Might this type be a function type, including after looking through newtypes and reducing type family applications?

In particular, returns True for IO a: after unwrapping the newtype, we get State# RealWorld -> (# State# RealWorld, a #), which is indeed a function type.

This function is conservative: it returns False only if the type is **definitely not** a function type. It returns True when it's not sure, e.g. for a type family application.

This function is generally used when we can perform certain optimisations when we are sure a type is not a function type (i.e. operationally does not take a value argument at runtime).

This is different from isFunTy, which only returns True when the type is a function arrow on-the-nose (without looking through newtypes). In particular, isFunTy returns False for IO () as well as for all type family applications.