Multiple return values
======================

Syntax for returning multiple values is trivial, it could be one of
the following:

    return 1 2    # this matches how function calls look like
    return 1, 2
    return [ 1 2 ]

But how about the following:

* How to define such functions: See func_sections.txt
* How to receive multiple return values to existing variables?
* How to receive multiple return values to new variables?
    - This can lead to quite long lines
    - But it could also be convenient.
    - But in C89 and Pascal you had to define the variables on separate
      lines in many cases and it worked fine.
* How to return all return values as-is?

Syntax test
-----------

Syntax 1:

    Int e1
    Bool e2

    [ e1 e2 ] = somefunc

    [ Int n1 Bool n2 ] = somefunc

    return somefunc

Syntax 2:

    Int e1
    Bool e2

    to e1
    to e2
    somefunc

    to Int n1
    to Bool n2
    somefunc

    return somefunc

Syntax 3:

    # Using ,= to make it less confusing for C, Java or C++ programmers
    Int e1
    Bool e2
    e1, e2 ,= somefunc
    Int n1, Bool n2 ,= somefunc
    return somefunc

Syntax 4:

    Int e1
    Bool e2
    e1 =, e2 = somefunc
    Int n1=, Bool n2 = somefunc
    return somefunc

Syntax 5:

    Int e1
    Bool e2
    e1, e2 ]= somefunc
    Int n, Bool n2 ]= somefunc
    return somefunc

Syntax 6:

    # Skip support for declarations of multiple variables on 1 line.
    Int e1
    Bool e2
    e1, e2 = somefunc
    Int n1
    Bool n2
    n1, n2 = somefunc
    return somefunc

Syntax 7:

    Int e1
    Bool e2
    e1, e2 = somefunc
    Int n1,
    Bool n2,
    = somefunc
    return somefunc

Syntax 8:

    # This leads to an ambiguity with array element assignment,
    # but maybe it can be solved somehow?
    Int e1
    Bool e2

    e1 e2 = somefunc
    arr i = somefunc

    return somefunc

Syntax 9:

    Int e1
    Bool e2

    set e1 e2 = somefunc

    return somefunc

Alternative solutions
---------------------

Alternative solution 1: Error/Context objects

    Int e1
    Bool e2

    e1 = somefunc
    e2 = ctx.get_xxx

    Int n1 = somefunc
    Bool n2 = ctx.get_xxx

    return somefunc    # context is available to the caller

Alternative solution 2: Make ad-hoc definitions of structs easy

    # Syntax 1: without names
    Pair Int Bool ep
    ep = somefunc
    Pair Int Bool np = somefunc
    return somefunc

    # Syntax 2: also without names
    Int/Bool ep
    ep = somefunc
    Int/Bool np = somefunc
    return somefunc

    # Syntax 3: also without names
    # a comma is still required to distinguish it from generic types
    (Int, Bool) ep
    ep = somefunc
    (Int, Bool) np = somefunc
    return somefunc

    # Syntax 4: record definitions, with names
    record SomeFuncReturn
        Int x
        Bool b
    end

    SomeFuncReturn ep
    ep = somefunc
    SomeFuncReturn np = somefunc
    return somefunc

Alternative solution 3: Don't support multiple-return values

Classes are quite easy to define in SLUL, so it might not be necessary.