The root module for the language of Fortran operators.

Language.Expression provides a way of forming expressions from what we call operators, via HFree.

For any type constructor op of kind (* -> *) -> * -> *, HFree op v a can be seen as an expression over op. op defines how we may combine different expressions. This is best illustrated with a simple example.

-- An operator type has two arguments. t is a type constructor used to refer
-- to expressions. a is the semantic type of the expression formed by the
-- operator.
data SimpleOp t a where
  -- Given two int expressions, we may add them. Notice how we refer to
  -- expressions recursively with the type constructor parameter t.
  Add :: t Int -> t Int -> SimpleOp t Int

  -- An operator does not have to actually combine expressions. It may produce
  -- an expression from a basic value, i.e. a literal int.
  Literal :: Int -> SimpleOp t Int

These modules define operators designed to be used as the higher-ranked functors for the higher-ranked free monads defined in Language.Expression. For example, HFree CoreOp v a is an expression over core Fortran operators with variables in v representing a computation of type a.

'Core' Fortran operators, that is operators that directly represent parts of