Hi!
I bet that the behavior I describe below is well known to fricas developers,
but I report this because I find it fun and awful at the same time...
1) WARM-UP:
IF I understand well, my UG's readings, SPAD and Aldor have **different
semantics** for commas. N>=2 below.
* in Aldor (expr1, expr2,..,exprN) is a tuple (multivalue) and {expr1;
expr2;..; exprN}
is a sequence of expression evaluated in that order. Parentheses () and braces
{} are
used for precedence's sake and 99% interchangeable (different behavior for
external trailing semicolon).
Aldor allows internal trailing semicolon in blocks {e1;e2;e3;} while this is an
error in spad.
* In Spad (expr1, expr2,..,exprN) is a tuple (not really, see point 2)
while {e1;..; eN} **AND** {e1,..,eN} are sequences of expressions evaluated in
the order.
OK, I find Aldor semantics much more clean & logic than that of Spad, but this
is not the problem.
2) THE MYSTERY:
The mysterious behavior is this one: one would expect that "{expression}" has a
value equal to "expression,
but this is NOT the case in the interpreter if "expression" is a tuple.
(1) -> {1;2;3} -- this is a sequence of expressions in a block, OK.
(1) 3
Type: PositiveInteger
(2) -> {1,2,3} -- this is a sequence of expressions in a block, OK.
(2) 3
Type: PositiveInteger
(3) -> 1,2,3 -- tuple
(3) [1, 2, 3]
Type: Tuple(PositiveInteger)
(4) -> (1,2,3) -- tuple
(4) [1, 2, 3]
Type: Tuple(PositiveInteger)
(5) -> {"bum"} --{expr} same as expr? YES
(5) "bum"
Type: String
(6) -> {(1,2,3)} --{expr} same as expr? NOOOO
(6) 3
Type: PositiveInteger
(7) -> ((1,2),(3,4)) --tuple of tuples
(7) [(1, 2), (3, 4)]
Type: Tuple(Tuple(PositiveInteger))
(8) -> {((1,2),(3,4))} -- tuple of tuples? NOOOOO
(8) [3, 4]
Type: Tuple(PositiveInteger)
In the example above I would have expected [1,2,3] as result of (6) and
[[1,2],[3,4]] as result of (8).
As a second choice I would have expected syntax errors because, for instance,
in (6) I try to see "(1" as first expression in a comma separated sequence
of expressions but it is not a well formed expression. Same for "((1,2)" in (8).
It is like the semantics of commas (,...,) for tuple is forgotten inside
a singleton block and mutated to that of a sequence.
weird feature...
regards
ric
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