module Syntax.TypeLevel.RowSyntax where
-- "row kinds" look like "Row k" where 'k' is another kind.
-- Usually, it's used with the kind, `Type`, to make Records (e.g. "Row Type")
-- You cannot find that much documentation on `Row` kinds because
-- they are built into the compiler.
type Example_of_an_Empty_Row :: forall k. Row k
type Example_of_an_Empty_Row = ()
type Example_of_a_Single_Row_of_Types = (fieldName :: ValueType)
type Example_of_a_Multiple_Row_of_Types = (first :: ValueType, second :: ValueType)
data Proxy :: forall k. k -> Type
data Proxy kind = Proxy
one_Key_Value_Pair :: Proxy (key :: Int)
one_Key_Value_Pair = Proxy
two_Key_Value_Pairs :: Proxy (key1 :: Int, key2 :: Int)
two_Key_Value_Pairs = Proxy
many_Key_Value_Pair :: Proxy ( key1 :: Int
, key2 :: String
-- , ...
, keyN :: (Int -> String)
many_Key_Value_Pair = Proxy
nested_Key_Value_Pair :: Proxy (outerKey :: Proxy (innerKey :: Int))
nested_Key_Value_Pair = Proxy
-- Since row kinds can be used with other kinds, one could also define
-- a row of Symbols:
type Example_of_a_Single_Row_of_Symbols = (a :: "a symbol")
type Example_of_a_Multiple_Row_of_Symbols = (a :: "a symbol", b :: "another symbol")
-- These can also be used with the quoted-key syntax (explained previously in the
-- Records folder):
type Quoted_Key_Row_of_Symbols = ("the key" :: "the symbol")
row_of_symbols_proxy :: Proxy ( firstField :: "this is a symbol"
, secondField :: "this is another symbol"
row_of_symbols_proxy = Proxy
Just like Symbol, Row's other type-level programming constructs
are defined in the built-in `Prim` package and the `purescript-prelude` library.
-- needed to compile
type ValueType = String