Data.Binding.Hobbits.Closed

This module uses Template Haskell to distinguish closed terms, so that the library can trust such functions to not contain any Name values in their closure.

Abstract types

data Cl a

The type Cl a represents a closed term of type a, i.e., an expression of type a with no free (Haskell) variables. Since this cannot be checked directly in the Haskell type system, the Cl data type is hidden, and the user can only create closed terms using Template Haskell, through the mkClosed operator.

Operators involving Cl

cl :: Q Exp -> Q Exp

cl is used with Template Haskell quotations to create closed terms of type Cl. A quoted expression is closed if all of the names occuring in it are

1) bound globally or 2) bound within the quotation or 3) also of type Cl.

clApply :: Cl (a -> b) -> Cl a -> Cl b

Closed terms are closed (sorry) under application.

unCl :: Cl a -> a

mbApplyCl :: Cl (a -> b) -> Mb ctx a -> Mb ctx b

mbApplyCl f b applies a closed function f to the body of multi-binding b. For example:

 mbApplyCl $(cl [| f |]) (nu $ \n -> n)   =   nu f

mbLiftClosed :: Mb ctx (Cl a) -> Cl a

mbLiftClosed is safe because closed terms don't contain names.

noClosedNames :: Cl (Name a) -> b

noClosedNames encodes the hobbits guarantee that no name can escape its multi-binding.

Synonyms

mkClosed :: Q Exp -> Q Exp

mkClosed = cl

type Closed = Cl

Closed = Cl

unClosed :: Cl a -> a

unClosed = unCl