<davekong>
I think shadowing is strange as it basically allows imperative style programming and means some variable can change value in a program
<davekong>
an accidental naming conflict can turn into a bug
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<whitequark>
davekong: shadowing allows you to freely compose code though.
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<davekong>
whitequark: what do you mean?
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<whitequark>
if a block of code contains no free variables, you can lexically "paste" it into any context and its meaning won't change.
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<ggole>
That's not terribly common though: even + and - are 'variables' in OCaml
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<whitequark>
bad wording. "if a block of code contains a set of free variables S, and they always have the same type in the surrounding environment", etc, etc
<whitequark>
same meaning :)
<ggole>
Mmm.
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<davekong>
If you don't have shadowing, you can compose and re-order code without worry.
<davekong>
The code won't compile if doing so would have caused an error
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<gasche>
davekong: but you have dangerous friends
<gasche>
the Coffeescript designers didn't like shadowing, so they forbid it and removed the "fresh variable" marker (let, var,...)
<gasche>
which means that in they system you can never compose and re-order code without worry
<gasche>
while in shadowing systems you can always safely compose closed code
<gasche>
(as you only have to worry about variable capture)
<gasche>
besides, warning on shadowing makes code maintenance more painful without automated tools
<gasche>
so if you require automated tools
<gasche>
you may as well allow shadowing and use those tools to detect shadowing situations when copy-pasting code
<adrien>
morning
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<levi>
That's what annoys me about all the silly minimalist syntax pseudo-functional languages.
<levi>
They don't bother learning about the subtleties involved in variable scope and just make stupid arbitrary decisions.
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<ggole>
Coffeescript has a construct for establishing a lexical variable binding, iirc
<ggole>
do or something like that
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<orbitz>
CoffeeScript seems like it's full of fail
<levi>
Well, it's not the fullest-of-fail thing I've every seen, but it's sad to see something close to nice be so flawed.
<levi>
Coming up with a nice language syntax is not as easy as it might seem, though. :P
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<orbitz>
Yes it is, SML's syntax was already handed to us by God
<orbitz>
The problem I see with CoffeeScript is this complete irrational fear of grouping symbols. If you don't support partial application I see no reason you should drop parens on a function call
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<wwilly>
bonjour
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<yezariaely>
is it possible to have types of higher kind in ocaml? (I know that I can use modules/functors to simulate that).
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<rixed>
yezariaely: what are types of higher kind, exactly?
<yezariaely>
a function from a type to a type.
<yezariaely>
e.g. type test 'a = 'a int
<yezariaely>
here, 'a is a function, because it is applied to an int.
<rixed>
what about a function from set of types to a set of types?
<ggole>
No, modules are the solution for that
<rixed>
a module is a set of types, so functors were actualy what I had in mind :)
<mrvn>
yezariaely: type 'a test = F : 'a -> 'a test?
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<mrvn>
type ('a, 'b) higher = ('a -> 'b)?
<yezariaely>
mrvn: here, 'a is still a ground type, i.e. int,string, or something user defined, but not a function from types to types.
<mrvn>
You can simulate type types with GADTs and some campl4 magic to build them automatically.
<mrvn>
Otherwise a functor is the only thing to do I think.
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<dsamarin>
"match (try Some (Queue.top bottomQ) with Queue.Empty -> None) with [...]"
<dsamarin>
Can someone help me understand this? I'm not an OCaml programmer but I need to read some OCaml code. I'd really appreciate it. :)
<ggole>
Queue.top returns the top element of a queue, returning an exception if there is no such element because the queue is empty.
<ggole>
That code maps the found-element/exception cases onto an option.
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<dsamarin>
ggole: Okay. Top meaning first?
<ggole>
Yep
<dsamarin>
Awesome, so the options appear to be: None , Some FlushEnded, and Some (Bottom (node,key))
<dsamarin>
None is matched when bottomQ has a top? (no exception)
<ggole>
None indicates "nothing here"
<ggole>
A bit like null in other languages, but more explicit
<ggole>
Some indicates a value, in this case the top element of the queue
<dsamarin>
Oh I misinterpreted the item that was being matched as a language exception
<ggole>
The point of doing this is to have the OCaml type system help out with case analysis
<dsamarin>
Last question, what's the difference between the last two options?
<ggole>
The stuff inside the option? That's program specific stuff.
<dsamarin>
I don't understand the meaning behind Some FlushEnded and Some (Bottom (node,key))
<dsamarin>
Oh these are elements you would find in the queue I bet
<ggole>
Yeah
<dsamarin>
Awesome thanks for your help
<ggole>
The match construct lets you look inside the option (Some _ or None) and the custom type at the same time
<ggole>
The point of doing it that way is that the type system can help you with the case analysis
<ggole>
Er, I said that already.
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<dsamarin>
Right, very convenient. So OCaml is dynamically typed
<adrien_oww>
no but it has more advanced type than many languages
<ggole>
Constructors like that are a little bit like the tagging in dynamic languages
<ggole>
But the type system keeps them separate
<ggole>
(And you get exhaustiveness and redundancy checking, which is very nice.)
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<mrvn>
adrien_oww: It is a bit like 'enum type {FlushEnded, Bottom}; struct data { type d_type; node d_node; }' but the d_node part is only accessible in ocaml when type is Bottom.
<mrvn>
And the Some/None would repsond to passing a &data or NULL in C.
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<hcarty>
Is there a prctl binding/wrapper for OCaml?
<hcarty>
Specifically to have the subprocesses of an OCaml process killed when the parent OCaml process is killed.
<adrien>
btw, which argument would you use to do that?
<hcarty>
adrien: Assuming that works as described :-)
<adrien>
well, I'm going to test it on tomorrow
<adrien>
we have a pygtk process which spawns a critical process; however there's a segfault in pygtk which takes the UI with it but not the critical process
<adrien>
(and I'm sure I'll have uses for other cases :-) )
<hcarty>
I think that there is a Python binding
<adrien>
looked in extunix?
<hcarty>
It was one of the results I found when looking for something in OCaml
<hcarty>
adrien: Yep, didn't see it tehre
<hcarty>
there
<adrien>
was likely your best bet unfortunately; that, or Core
<adrien>
and maybe ocmalnet
<adrien>
ocamlnet*
<rks`>
(if it's in core, it's probably in Linux_ext)
<mrvn>
if you have bindings then I can merge them to extunix.
<rks`>
(there are some stubs using prctl in linux_ext in core)
<hcarty>
mrvn: If I write something I'll pass it along
<hcarty>
rks`: Thanks for the tip about where to look in Core. I'm not using it but I may be able to pinch the relevant bit of code if it's already there.
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<smondet>
hcarty: (not sure) but Unix.setsid should create a process group, then
<smondet>
when you should be able to kill the whole group (process + children)
<smondet>
s/when//
<hcarty>
smondet: Thanks, I'll take a look at that
<hcarty>
I misread the documentatio... it looks like prctl needs to be called from the child process rather than the parent to have this work.
<adrien>
I read it that way
<hcarty>
I have at least a few cases where that's not a (simple) option. On to testing process groups!
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<hcarty>
adrien: Wishful reading on my part
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<adrien>
that's why I had to ask you about it but I think something else in prctl might do it
<levi>
I was so happy to find fieldslib last night.
<adrien>
hcarty: maybe through CHILD_SUBREAPER
<adrien>
PR_SET_CHILD_SUBREAPER (since Linux 3.4)
<adrien>
ouch
<adrien>
might be too recent
<levi>
I had a record type that stored a bunch of configuration parameters, and I wanted to merge the defaults instance with the instances from reading the command line and reading the config file, but there seemed no clean way of doing it without typing the field names about 4 times each.
<hcarty>
adrien: Yep, too recent unfortunately. Needs to be able to run on RHEL 6/CentOS 6.
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<hcarty>
It looks like Unix.setsid ... (set sigX handler) ... Unix.kill 0 Sys.sigX ... (reset sigX handler) ... (continue on) ... may work
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<hcarty>
For anyone interested, that set of steps does seem to work at least one level deep.
<hcarty>
One level of child processes that is. I haven't tested processed nested more deeply than that.
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<Drup>
Does anyone know a simple http/rest client library ?