LOL. i am trying this:
instance [U, V with Str[U]] Str[U ** V] {
fun str (x: U ** V) =>
match x with
| ?a ,, ?b => str a +", " + str b
endmatch
;
}
/*
instance[T,U] Str[T*U] {
fun str (t:T, u:U) => "("+str t + ", " + str u+")";
}
*/
Somehow this breaks my test program (I get an overload error in C++
for an assignment). Strangely enough Felix builds and some tests seem
to work .. some not:
Cannot find type double * string^2 in registry
Error 1 in flx: Operation not permitted
* build/release/bin/flx --test=build/release:
build/release/test/regress/rt/objects-01.flx ->
build/release/test/regress/rt/objects-01
This works tho:
var x =
1,2.3, "Hello",
1,2.3, "Hello",
1,2.3, "Hello",
1,2.3, "Hello",
1,2.3, "Hello",
1,2.3, "Hello",
1,2.3, "Hello"
;
println$ x;
But in any case there's a problem! The tuple cons
instance using ** doesn't put the parens in!
It's not cool, because (1,("2",3.3)) will print as
1,2,3.3
which is wrong. Its not possible for this routine to put in the parens
because it calls itself on the tail which would make a "(" before every element.
The workaround is the usual one in all computer science: if you can't
make the dang thing work, KICK IT. That doesn't fix anything, but it
makes you feel better.
Then, try indirection :)
We need Str [U **V] to call InnerStr[U ** V] which has function inner_str
which defaults to str, but is specialised on U ** V to produce the comma list,
whilst the outer Str:: str instance just puts in the parens.
--
john skaller
[email protected]
http://felix-lang.org
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