GHC.Types.Basic

A *one-index* constructor tag

Type of the tags associated with each constructor possibility or superclass selector

A *zero-indexed* constructor tag

Tags are allocated from here for real constructors or for superclass selectors

The number of value arguments that can be applied to a value before it does "real work". So: fib 100 has arity 0 x -> fib x has arity 1 See also Note [Definition of arity] in GHC.Core.Opt.Arity

Syntactic (visibility) arity, i.e. the number of visible arguments. See Note [Visibility and arity]

Representation Arity

The number of represented arguments that can be applied to a value before it does "real work". So: fib 100 has representation arity 0 x -> fib x has representation arity 1 (# x, y #) -> fib (x + y) has representation arity 2

The number of arguments that a join point takes. Unlike the arity of a function, this is a purely syntactic property and is fixed when the join point is created (or converted from a value). Both type and value arguments are counted.

FullArgCount is the number of type or value arguments in an application, or the number of type or value binders in a lambda. Note: it includes both type and value arguments!

A power-of-two alignment

Is a TyCon a promoted data constructor or just a normal type constructor?

Recursivity Flag

Was this piece of code user-written or generated by the compiler?

See Note [Generated code and pattern-match checking].

Whether to run pattern-match checks in generated code.

See Note [Generated code and pattern-match checking].

Does this Origin require us to run pattern-match checking, or should we skip these checks?

See Note [Generated code and pattern-match checking].

This metadata stores the information as to why was the piece of code generated It is useful for generating the right error context See Part 3 in Note [Expanding HsDo with XXExprGhcRn] in GHC.Tc.Gen.Do

Should an argument be passed evaluated *and* tagged.

A general-purpose pretty-printing precedence type.

Are we dealing with an unboxed tuple or an unboxed sum?

Used when validity checking, see check_ubx_tuple_or_sum.

Pretty print an alternative in an unboxed sum e.g. "| a | |".

If the Id is a lambda-bound variable then it may have lambda-bound variable info. Sometimes we know whether the lambda binding this variable is a "one-shot" lambda; that is, whether it is applied at most once.

This information may be useful in optimisation, as computations may safely be floated inside such a lambda without risk of duplicating work.

See also Note [OneShotInfo overview] above.

It is always safe to assume that an Id has no lambda-bound variable information

identifier Occurrence Information

Keep only the most robust occurrence info: deadness, loop-breaker-hood.

In particular, it zaps TailCallInfo: see Note [JoinId vs TailCallInfo] in GHC.Core.Opt.Simplify.Env.

Inside Lambda

Interesting Context

Embedding Projection pair

Default Method Specification

An integer or infinity

A representation of infinity

Turn a positive number into an IntWithInf, where 0 represents infinity

Inject any integer into an IntWithInf

Subtract an Int from an IntWithInf

Multiply an IntWithInfo by an Int

Flag to see whether we're type-checking terms or kind-checking types

Paints a picture of what a TyCon represents, in broad strokes. This is used towards more informative error messages.

Whether something is a type or a data declaration, e.g. a type family or a data family.

When we only care whether a data-type declaration is data or newtype, but not what constructors it has.

Get the enclosing class TyCon (if there is one) for the given TyConFlavour

Specify whether to default type variables of kind RuntimeRepLevityMultiplicity.

Specify whether to default kind variables, and type variables of kind RuntimeRepLevityMultiplicity.

Foreign formats supported by GHC via TH

ImportLevel