The Prim.Row module is embedded in the PureScript compiler. Unlike Prim, it is not imported implicitly. It contains automatically solved type classes for working with row types.


class Union (left :: Row k) (right :: Row k) (union :: Row k) | 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.


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

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


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

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


class Cons (label :: Symbol) (a :: k) (tail :: Row k) (row :: Row k) | 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.