Data.KindID.Class

This module contains the type-level mechanisms that are used to define custom KindID-ish identifier types.

Prefix

type ValidPrefix prefix = (KnownSymbol prefix, LengthSymbol prefix < 64, IsLowerSymbol prefix ~ 'True)

A constraint for valid prefix Symbols.

class ToPrefix a

A class that translates any kind to a Symbol. It is used to translate custom data kinds to a Symbol so that they can be used as KindID prefixes.

For example, suppose we have the following data structure that represents the prefixes we are going to use:

data Prefix = User | Post | Comment

Then we can make it an instance of ToPrefix like this:

instance ToPrefix 'User where
  type PrefixSymbol 'User = "user"

instance ToPrefix 'Post where
  type PrefixSymbol 'Post = "post"

instance ToPrefix 'Comment where
  type PrefixSymbol 'Comment = "comment"

Now we can use Prefix as a prefix for KindIDs, e.g.

do
  userID <- genKindID @'User -- Same as genKindID @"user"
  postID <- genKindID @'Post -- Same as genKindID @"post"
  commentID <- genKindID @'Comment -- Same as genKindID @"comment"

Associated Types

type PrefixSymbol a :: Symbol

Instances

ToPrefix (a :: Symbol)

The PrefixSymbol of a Symbol is the Symbol itself.

Defined in Data.KindID.Class

Associated Types

type PrefixSymbol a :: Symbol

Helpers

type family LengthSymbol (prefix :: Symbol) :: Nat where ...

The length of a Symbol as a Nat.

Equations

LengthSymbol prefix = LSUH (UnconsSymbol prefix)

type family IsLowerSymbol (prefix :: Symbol) :: Bool where ...

Is a Symbol lower case?

Equations

IsLowerSymbol prefix = ILSUH (UnconsSymbol prefix)

type family IsLowerChar (ch :: Char) :: Bool where ...

Is a type-level Char lower case?

Equations

IsLowerChar ch = (Compare '`' ch == 'LT) && (Compare ch '{' == 'LT)

type family LSUH (uncons :: Maybe (Char, Symbol)) :: Nat where ...

Length Symbol Uncons Helper.

Equations

LSUH 'Nothing = 0

LSUH ('Just '(c, s)) = 1 + LengthSymbol s

type family ILSUH (uncons :: Maybe (Char, Symbol)) :: Bool where ...

Is Lower Symbol Uncons Helper.

Equations

ILSUH 'Nothing = 'True

ILSUH ('Just '(c, s)) = IsLowerChar c && IsLowerSymbol s