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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.
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