Copilot.Language.Operators.Struct

Combinators to deal with streams carrying structs.

We support two kinds of operations on structs: reading the fields of structs and modifying the fields of structs.

To obtain the values of field x of a struct s, you can just write:

expr = s # x

If you want to update it, use instead a double hash to refer to the field. You can either update the field:

expr = s ## x =: 75

To update it by applying a function to it, for example, the function that updates a stream by one unit, just do:

expr = s ## x =$ (+1)

Documentation

(#) :: (KnownSymbol f, Typed t, Typed s, Struct s) => Stream s -> (s -> Field f t) -> Stream t

Create a stream that carries a field of a struct in another stream.

This function implements a projection of a field of a struct over time. For example, if a struct of type T has two fields, t1 of type Int and t2 of type Word8, and s is a stream of type Stream T, then s # t2 has type Stream Word8 and contains the values of the t2 field of the structs in s at any point in time.

data Projection s f t

Type represented an unapplied struct field accessor and a stream carrying structs.

(##) :: (KnownSymbol f, Typed t, Typed s, Struct s) => Stream s -> (s -> Field f t) -> Projection s f t

Pair a stream with a field accessor, without applying it to obtain the value of the field.

This function is needed to refer to a field accessor when the goal is to update the field value, not just to read it.

(=:) :: (KnownSymbol f, Typed t, Typed s, Struct s) => Projection s f t -> Stream t -> Stream s infixl 8

Create a stream where the field of a struct has been updated with values from another stream.

For example, if a struct of type T has two fields, t1 of type Int32 and t2 of type Word8, and s is a stream of type Stream T, and $sT1$ is a stream of type Int32 then s ## t2 =: sT1 has type Stream T and contains structs where the value of t1 is that of sT1 and the value of t2 is the value that the same field had in s, at any point in time.

(=$) :: (KnownSymbol f, Typed t, Typed s, Struct s) => Projection s f t -> (Stream t -> Stream t) -> Stream s infixl 8

Create a stream where the field of a struct has been updated by applying a function to it.

For example, if a struct of type T has two fields, t1 of type Int32 and t2 of type Word8, and s is a stream of type Stream T, and $f$ is a function from Stream Int32 -> Stream Int32 then s ## t2 =$ f has type Stream T and contains structs where the value of t1 is that of f applied to the original value of t1 in s, and the value of t2 is the value that the same field had in s, at any point in time.