This problem is related to the problem I mentioned earlier in regard to
upgrading list.factor. I am now upgrading symtab.factor
(www.rosycrew.org/symtab.factor) and it won't compile. All of the functions
involved in finding a key in the tree fail, and all for the same reason
("unbalanced branches"). These are a couple of the functions that are
failing::
:: <find-key> ( root target -- node new-root | 0 )
... ;
: find-key ( key root -- node new-root | 0 )
dup 0 = [ nip ] [ swap <find-key> ] if ;
The vertical bar in the stack-frame means "OR." The idea is that the word
either returns two values (node and new-root) OR it returns one value (0).
This is pretty typical in Forth, and Factor is derived from Forth, so I
would hope for it to work here also.
In C the work-around is to return a pointer to a struct that contains the
two values (node and new-root), or to return a 0 (null pointer) in the event
that the key isn't found. This has to be done because C doesn't support
returning multiple values. Also, C is a strongly-typed language, so you
can't return a struct or a 0, because they are different types --- you can
only return a pointer to a struct or a 0, because the 0 is considered to be
a null pointer to any type. All of this is very kludgy though. I would
really want to avoid messing around with structs (or tuples) at all, and
just return the values on the stack, the way that I would do in Forth.
The problem in Factor seems to be related to returning a variable number of
values (two or one), rather than returning multiple values, which Factor
seems to be okay with.
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