Syntax for Handling Multiple Returns

[DavePearce]

(follows on from #87)

At the moment, it is valid in WyAL to declare a function with multiple returns, such as:

function f(int x) -> (int y, int z)

However, at this stage, there is not syntax for extracting the individual elements of a function which has multiple returns. For example, suppose this Whiley:

   ...
   x,y = f(0)
   ...

Then we'd want to generate an expression of the form (x == f(0)#0) && (y == f(0)#1) where the # indicates the return selector. The key here is really that every function invocation in WyAL must refer to an individual return value. This is because there are no tuple values at this time.

Proposed Syntax

Options:

(x == f(0)#0) && (y == f(0)#1)

(x == f(0):0) && (y == f(0):1)

(x == f(0)'0) && (y == f(0)'1)

Amazingly, the latter does not look that bad!!

[DavePearce]

Sadly, in the end I went with the # syntax because the ' syntax was conflicting with single character literals.