first-class-families-0.8.0.1: First-class type families

Safe Haskell | Safe-Inferred
Language | Haskell2010

Fcf.Utils

Contents

- From Data.Type.Bool

Description

Miscellaneous families.

Synopsis

- data Error :: Symbol -> Exp a
- data TError :: ErrorMessage -> Exp a
- data Constraints :: [Constraint] -> Exp Constraint
- data TyEq :: a -> b -> Exp Bool
- type family Stuck :: a
- class IsBool (b :: Bool) where
  - _If :: (b ~ 'True => r) -> (b ~ 'False => r) -> r
- data Case :: [Match j k] -> j -> Exp k
- data Match j k
- type (-->) = 'Match_ :: j -> k -> Match j k
- type Is = 'Is_ :: (j -> Exp Bool) -> k -> Match j k
- type Any = 'Any_ :: k -> Match j k
- type Else = 'Else_ :: (j -> Exp k) -> Match j k
- type family If (cond :: Bool) (tru :: k) (fls :: k) :: k where ...

# Documentation

data Error :: Symbol -> Exp a Source #

Type-level `error`.

#### Instances

Instances details

type Eval (Error msg :: a -> Type) Source # |
Instance details Defined in Fcf.Utils type Eval (Error msg :: a -> Type) = TypeError ('Text msg) :: a

data TError :: ErrorMessage -> Exp a Source #

`TypeError` as a fcf.

#### Instances

Instances details

type Eval (TError msg :: a -> Type) Source # |
Instance details Defined in Fcf.Utils type Eval (TError msg :: a -> Type) = TypeError msg :: a

data Constraints :: [Constraint] -> Exp Constraint Source #

Conjunction of a list of constraints.

#### Instances

Instances details

type Eval (Constraints (a ': as) :: Constraint -> Type) Source # |
Instance details Defined in Fcf.Utils type Eval (Constraints (a ': as) :: Constraint -> Type) = (a, Eval (Constraints as))
type Eval (Constraints ('[] :: [Constraint])) Source # |
Instance details Defined in Fcf.Utils type Eval (Constraints ('[] :: [Constraint])) = ()

data TyEq :: a -> b -> Exp Bool Source #

Type equality.

### Details

Expand

The base library also defines a similar `(`==`)`; it differs from `TyEq` in the following ways:

- `TyEq` is heterogeneous: its arguments may have different kinds;
- `TyEq` is reflexive: `TyEq a a` always reduces to `True` even if `a` is a variable.

#### Instances

Instances details

type Eval (TyEq a b :: Bool -> Type) Source # |
Instance details Defined in Fcf.Utils type Eval (TyEq a b :: Bool -> Type)

type family Stuck :: a Source #

A stuck type that can be used like a type-level `undefined`.

class IsBool (b :: Bool) where Source #

Methods

_If :: (b ~ 'True => r) -> (b ~ 'False => r) -> r Source #

#### Instances

Instances details

IsBool 'False Source # |
Instance details Defined in Fcf.Utils Methods _If :: ('False ~ 'True => r) -> ('False ~ 'False => r) -> r Source #
IsBool 'True Source # |
Instance details Defined in Fcf.Utils Methods _If :: ('True ~ 'True => r) -> ('True ~ 'False => r) -> r Source #

data Case :: [Match j k] -> j -> Exp k Source #

(Limited) equivalent of `\case { .. }` syntax. Supports matching of exact values (`-->`) and final matches for any value (`Any`) or for passing value to subcomputation (`Else`). Examples:

    type BoolToNat = Case
      [ 'True  --> 0
      , 'False --> 1
      ]

    type NatToBool = Case
      [ 0 --> 'False
      , Any   'True
      ]

    type ZeroOneOrSucc = Case
      [ 0  --> 0
      , 1  --> 1
      , Else   ((+) 1)
      ]

#### Instances

Instances details

type Eval (Case ms a :: k -> Type) Source # |
Instance details Defined in Fcf.Utils type Eval (Case ms a :: k -> Type)

data Match j k Source #

type (-->) = 'Match_ :: j -> k -> Match j k infix 0 Source #

Match concrete type in `Case`.

type Is = 'Is_ :: (j -> Exp Bool) -> k -> Match j k Source #

Match on predicate being successful with type in `Case`.

type Any = 'Any_ :: k -> Match j k Source #

Match any type in `Case`. Should be used as a final branch.

Note: this identifier conflicts with `Any` (from Fcf.Class.Foldable) `Any` (from Data.Monoid), and `Any` (from GHC.Exts).

We recommend importing this one qualified.

type Else = 'Else_ :: (j -> Exp k) -> Match j k Source #

Pass type being matched in `Case` to subcomputation. Should be used as a final branch.

# From Data.Type.Bool

type family If (cond :: Bool) (tru :: k) (fls :: k) :: k where ... Source #

Type-level If. `If True a b` ==> `a`; `If False a b` ==> `b`

Equations

If 'True (tru :: k) (fls :: k) = tru |
If 'False (tru :: k) (fls :: k) = fls |