Having too much fun with Makam…
Conversation
It's interesting that check and synth end up having the same signature here...
1
1
yeah, they have different modes though - like:
check : in -> in -> in -> mode.
synth : in -> in -> out -> mode.
(if Makam had support for this, like in Mercury)
2
Are modes restrictive or merely descriptive? Like, if you try to use `check` to synthesize a type, will it (a) fail with some bad error message, where an explicit mode would've resulted in a better one, or (b) succeed, but you'd've preferred it didn't by specifying the mode?
1
(Or do they have some other purpose besides these?)
1
Makam does not have modes - this was invented syntax, hehe. In the case of Mecury it uses them to generate different implementations of the same predicate. You can have multiple mode decls for the same predicate. If you try to use a mode that is not in that list it's an error.
2
1
This is in contrast to Makam and Prolog where the information seems to flow (?) dynamically. This is more expressive than Mercury, but harder to make run fast, from speaking to Mercury folks at work.
1
1
In my tests I'm sometimes using `check` with an output mode so that I can cover both check and synth at the same time, but that fails for more complicated terms that could be ambiguous (Makam will try searching forever I think?) gist.github.com/brendanzab/7a3
1
1
I do find that I somtimes will do a typo and that results in a foreverlööp, and I _think_ the mode checker from Mercury would catch some of that. Or maybe I'm thinking of the determinism checker…
1
Like, maybe it would be better to say:
check : in -> in -> in -> semidet.
synth : in -> in -> out -> semidet.
To say that both of those might fail, but are otherwise deterministic. Check with an output mode for the type would be:
check : in -> in -> out -> nondet.
1
1
For more reading on how Mercury does it, you can have a look at the docs: mercurylang.org/information/do
Note that I'm not a Mercury developer, so I could be getting some of this wrong! knows more about this than me!
1
2
Yep. As says, each predicate may have more than one mode in Mercury, each mode has exactly one determinism (can fail, will not fail, may have multiple answers etc).
Each time you use a predicate the compiler can figure out which mode of that predicate you need.
1
2
Show replies