Signatures are called APIs in Mythryl, for conciseness and improved C intuition.
Pursuing the theme that generics (“functors”) are compile-time functions with package (“structure”) values taking API (“signature”) types, Mythryl APIs take Mixed_Case names just like Mythryl types.
Named APIs are declared using a conventional, compact, Posix-flavored syntax:
api My_Api {
Color; # Opaque type declaration.
Point = TWO_D (Float, Float) # Transparent type declaration.
| THREE_D (Float, Float, Float);
my_function: List(Int) -> Int; # Function declaration.
}; # All statements end with a semicolon!
To avoid spending an extra reserved word (as does SML with signature and sig) Mythryl uses a simple variant of the above syntax to declare anonymous APIs, merely replacing the API name with the standard underbar wildcard:
api {
Color; # Opaque type declaration.
Point = TWO_D (Float, Float) # Transparent type declaration.
| THREE_D (Float, Float, Float);
my_function: List(Int) -> Int; # Function declaration.
}; # All statements end with a semicolon!
A Mythryl file declaring an API customarily uses the .api file extension.
Note that despite the use of vertical bar (| ) in the above syntax, it is not a reserved word in Mythryl, and may be freely defined by the application programmer. The default Mythryl library definition is integer inclusive-or, in line with C intuition.