Type Macro

Verse has a special construct that can be used to get the type of an arbitrary expression (similar to decltype in modern C++): type. It can be used anywhere a type can be used. For example,

Foo() : int = 0
Bar(X : type{Foo()}) : type{Foo()} = X
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Foo() : int = 0 Bar(X : type{Foo()}) : type{Foo()} = X

It is particularly useful to describe the types of functions, and it is required to give the result type of a function as another function with non-default effects. For example,

comparison := enum:
    LT
    EQ
    GT

Less(X : int, Y : int)<decides> : int =
    X < Y

Equal(X : t, Y:comparable where t:subtype(comparable))<decides> : t =
    X = Y

Greater(X : int, Y : int)<decides> : int =
    X > Y

Comparison(Arg : comparison) : type{_(:int, :int)<decides> : int} =
    case (Arg):
        comparison.LT => Less
        comparison.EQ => Equal
        comparison.GT => Greater
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comparison := enum: LT EQ GT Less(X : int, Y : int)<decides> : int = X < Y Equal(X : t, Y:comparable where t:subtype(comparable))<decides> : t = X = Y Greater(X : int, Y : int)<decides> : int = X > Y Comparison(Arg : comparison) : type{_(:int, :int)<decides> : int} = case (Arg): comparison.LT => Less comparison.EQ => Equal comparison.GT => Greater

Here, the comparison function converts a comparison enumeration to the comparison operation each particular enumeration value corresponds to. This example also makes use of the special _ identifier, which can be used in type in places where an identifier is expected without having to actually provide a name that is otherwise unused.