Type.Row

class ListToRow (list :: RowList) (row :: Row Type) | list -> row

Convert a RowList to a row of types. The inverse of this operation is RowToList.

Instances

• ListToRow Nil ()
• (ListToRow tail tailRow, Cons label ty tailRow row) => ListToRow (Cons label ty tail) row

class RowListRemove (label :: Symbol) (input :: RowList) (output :: RowList) | label input -> output

Remove all occurences of a given label from a RowList

Instances

• RowListRemove label Nil Nil
• (RowListRemove label tail tailOutput, Equals label key eq, If eq (RLProxy tailOutput) (RLProxy (Cons key head tailOutput)) (RLProxy output)) => RowListRemove label (Cons key head tail) output

class RowListSet (label :: Symbol) (typ :: Type) (input :: RowList) (output :: RowList) | label typ input -> output

Add a label to a RowList after removing other occurences.

Instances

• (TypeEquals (SProxy label) (SProxy label'), TypeEquals typ typ', RowListRemove label input lacking) => RowListSet label typ input (Cons label' typ' lacking)

class RowListNub (input :: RowList) (output :: RowList) | input -> output

Remove label duplicates, keeps earlier occurrences.

Instances

• RowListNub Nil Nil
• (TypeEquals (SProxy label) (SProxy label'), TypeEquals head head', TypeEquals (RLProxy nubbed) (RLProxy nubbed'), RowListRemove label tail removed, RowListNub removed nubbed) => RowListNub (Cons label head tail) (Cons label' head' nubbed')

class RowListAppend (lhs :: RowList) (rhs :: RowList) (out :: RowList) | lhs rhs -> out

Instances

• (TypeEquals (RLProxy rhs) (RLProxy out)) => RowListAppend Nil rhs out
• (RowListAppend tail rhs out', TypeEquals (RLProxy (Cons label head out')) (RLProxy out)) => RowListAppend (Cons label head tail) rhs out

type RowApply (f :: Row Type -> Row Type) (a :: Row Type) = f a

Type application for rows.

Operator alias for Type.Row.RowApply (right-associative / precedence 0)

Applies a type alias of open rows to a set of rows. The primary use case this operator is as convenient sugar for combining open rows without parentheses.

type Rows1 r = (a :: Int, b :: String | r)
type Rows2 r = (c :: Boolean | r)
type Rows3 r = (Rows1 + Rows2 + r)
type Rows4 r = (d :: String | Rows1 + Rows2 + r)

class Cons (label :: Symbol) (a :: Type) (tail :: Row Type) (row :: Row Type) | label a tail -> row, label row -> a tail

The Cons type class is a 4-way relation which asserts that one row of types can be obtained from another by inserting a new label/type pair on the left.

class Lacks (label :: Symbol) (row :: Row Type) 

The Lacks type class asserts that a label does not occur in a given row.

class Nub (original :: Row Type) (nubbed :: Row Type) | original -> nubbed

The Nub type class is used to remove duplicate labels from rows.

class Union (left :: Row Type) (right :: Row Type) (union :: Row Type) | left right -> union, right union -> left, union left -> right

The Union type class is used to compute the union of two rows of types (left-biased, including duplicates).

The third type argument represents the union of the first two.

data Nil :: RowList

The empty RowList.

data Cons :: Symbol -> Type -> RowList -> RowList

Constructs a new RowList from a label, a type, and an existing tail RowList. E.g: Cons "x" Int (Cons "y" Int Nil).

class RowToList (row :: Row Type) (list :: RowList) | row -> list

Compiler solved type class for generating a RowList from a closed row of types. Entries are sorted by label and duplicates are preserved in the order they appeared in the row.

data RowList :: Type

A type level list representation of a row of types.

data RProxy (row :: Row Type)

A proxy data type whose type parameter is a type of kind # Type (a row of types).

Commonly used for specialising a function with a quantified type. For example, suppose we have an identity function for records of type:

recordIdentity :: forall row . RProxy row -> Record row -> Record row
recordIdentity _ rec = rec

Then applying this function to an RProxy with a specialised type allows us to specify a concrete type for row:

:t recordIdentity (RProxy :: RProxy ( x :: Int, y :: Int ))
{ x :: Int, y :: Int } -> { x :: Int, y :: Int }

Here row has been specialised to ( x :: Int, y :: Int ).

Constructors

• RProxy

data RLProxy (rowlist :: RowList)

A proxy data type whose type parameter is a type of kind RowList.

Commonly used for specialising a function with a quantified type.

Constructors

• RLProxy