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<eikke>
in core, Fn.const is defined as "let const c = (); fun _ -> c". Why the unit?
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<flux>
maybe it has something to do with partial egaluation/application and the generatedcode
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<wmeyer>
hello
<introom>
what's the meaning of using "let _" let _ = List.iter (fun s -> printf "%s\n" s) my_data
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<orbitz>
introom: means they don't care about the result
<jpdeplaix>
introom: here it's useless since we can use « let () = », but in general it's used when we don't want to bother about the result
<orbitz>
shoudl probbaly have been written let () = List ... or ignore (List ..)
<jpdeplaix>
:D
<wmeyer>
it just creates binding, so you can enforce that the operation in the next scope goes after. The _ is a in-exhaustive pattern match, and it's telling the compiler to match anything (is polymorphic) and throw away the value
<introom>
jpdeplaix: why () can do it? shouldn't () immutable?
<wmeyer>
so basically, the operations separated by ";" can be transformed to sequence of lets, the _ is very useful when you don't know the type of the calue or you just don't care about the value. In either ways.
<wmeyer>
introom: () is a single constructor of unit. Unit type has just single value of ()
<jpdeplaix>
introom: this is not an assignation, it's a binding
<wmeyer>
so if your expression is unit, you can write () instead of _, but if you don't want this constraint, you can still write _
<wmeyer>
jpdeplaix: is right, let's just introduce "named value"
<wmeyer>
s/let's/lets
<introom>
wmeyer: I somewhat get it.
<wmeyer>
so if you had this type
<introom>
and seems _ itself is discarded. let _ = "sdf";; and if I do _;; will raise parse error in utop
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<wmeyer>
type singleton = S
<wmeyer>
is isomorhic to unit
<wmeyer>
has single constructor without arguments
<wmeyer>
then you could say let S = <expression that type is "singleton">
<wmeyer>
the same with ()
<wmeyer>
but if you say _, you also don't care about the type
<wmeyer>
in a global scope, it's a fine way of implementing blocks of expressions without using too much ;;
<introom>
ype singleton = S | Sme of int;; let S = Sme 3;; it raises "not exhaustive warning"
<introom>
s/^/t/
<wmeyer>
so you can say let _ = let x = 1 in let y = 2 in let s = x + y in let foo = string_of_int s
<wmeyer>
yes, because singleton now has two constructors
<wmeyer>
and let can match only single one
<wmeyer>
that is called in-exhaustive pattern
<wmeyer>
therefore let is only applicable where you cover all the possible cases for the match
<wmeyer>
otherwise you risk failing to match but *at runtime*
<introom>
and let can match only single one ??
<introom>
it says "Sme _" is not matched.
<wmeyer>
so let ahs special case of patterns, called irrefutable
<wmeyer>
yes, let just binds, it's just convenience it can match
<wmeyer>
and deconstruct values
<ggole>
Almost always used for tuples
<ggole>
(And 'newtype' style wrappers, I guess)
<wmeyer>
actually it might be very useful with GADTS where the only way to use GADT is through constructor, and sometimes there is just single one
<ggole>
Oh, good point
<introom>
goes out of my understanding.
<wmeyer>
introom: GADTS are fairly new, and complicated for the new users :-)
<ggole>
You can pretty much ignore them until you are more fluent in the language
<wmeyer>
(and not used that often in practice at the moment)
<introom>
I can understand the bind thing for let x = 1 in ... but why do you say let () = <some expr returns () ) is also a bind?
<introom>
I mean, there is no "in"
<ggole>
let at the top level is a special case
<ggole>
If there is no in, it refers to the rest of the file (or input, if you are at the repl)
<introom>
just the above example, x points to 1, and () """points to "" () ??
<ggole>
The second let does not bind any variables
<introom>
just an assert that the expression should return () ?
<ggole>
Yeah
<wmeyer>
yes, a sort of static assert
<ggole>
Which is a bit more specific than let _ = ...
<introom>
got it. that's what wmeyer called *match*
<ousado>
let () = expr is saying that the expression exists for its side-effects only
<wmeyer>
because there is no conditional code on () ever :-)
<wmeyer>
so, the value itself is useless, but exists
<wmeyer>
so it might be used for marking some placeholder or arguments
<ggole>
Well, some people like to use unit refs as unique values
<ggole>
Although that's pretty horrible
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<wmeyer>
it surpisingly has it's applications even in purely functional languages
<wmeyer>
don't forget ggole that there is always second identifier to use, unit
<wmeyer>
where on type level you can throw away type parameters you don't care abot
<ggole>
Yeah, true. At the value level, though, losing the ability to have sets and maps is a major downside.
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<hcarty>
def-lkb_: Using merlin 1.1 + vim + syntastic, is it possible to jump to errors? :lnext/:lprev say that there is no location list.
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<rks`>
hcarty: which version of syntastic/vim are you using?
<rks`>
(the error report mechanism hasn't changed in merlin since version 1.0)
<rks`>
also: "it's working for me"
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<hcarty>
rks`: vim 7.3, syntastic is 3.0.0 I think
<def-lkb_>
hcarty: try after setting :let g:syntastic_auto_loc_list=1
<hcarty>
def-lkb_: That works! And gives me a list at the bottom of the window.
<hcarty>
def-lkb_, rks`: Thank you both
<def-lkb_>
hcarty: you're welcome :)
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<rks`>
I didn't do much, but ok :)
<travisbrady>
def-lkb_: do you use merlin w/ ocp-indent?
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<rks`>
travisbrady: we tried to, but having ocp-indent work with vim is not that easy.
<rks`>
(or wasn't, last time I tried)
<def-lkb_>
travisbrady: for some time I tried, it was possible to get something quite efficient… but there is a lot of work to integrate it properly
<def-lkb_>
so I think it would be cool to have proper support for ocp-indent, but that's not possible at the moment (you can still the default ocp-indent script, it shall work independently of merlin)
<def-lkb_>
use*
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<travisbrady>
Ahh. so do you have syntastic or merlin handling indentation for you?
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<def-lkb_>
not anymore, worked at some point in the past, but code rote :/
<def-lkb_>
can't speak for rks`, but I am still using default vim indentation
<hcarty>
travisbrady: I'm using merlin + ocp-indent as separate plugins and it works (mostly) well.
<hcarty>
travisbrady: But the default/auto-indentation still comes from vim. I need to explictly tell vim to use ocp-indent.
<rks`>
def-lkb_: me too.
<rks`>
hcarty: yes, that's what we were trying to avoid
<rks`>
we wanted ocp-indent to do the auto-indent
<hcarty>
rks`: That would be nice
<def-lkb_>
definitely possible, but needs some work...
<gasche>
def-lkb_: what kind of work?
<travisbrady>
I've been using a bit of ocp-indent but sometimes it does some strange things and I have to fix it manually.
<hcarty>
travisbrady: For what it's worth, when I've run into that I've found the authors respond quickly to issues on github.
<def-lkb_>
gasche: two things, independent of merlin, I would like some checkpointing system to speed up ocp-indent (it can feels slow on thousand long files and it is wasting power)
<def-lkb_>
gasche: second, I have the feeling that indentation can be used as a much more robust heuristic for syntax correction than current tricks on grammar, and there is a lot to be learned from ocp-indent
<rks`>
def-lkb_: I think he just wondered about the changes necessary to have ocp-indent working with vim
<rks`>
not about how it could be used by merlin.
<def-lkb_>
rks`: point 1
<rks`>
yes yes, I was merely mentionning that your 2nd point was useless :}
<def-lkb_>
rks`: réglisse
<rks`>
:D
<gasche>
I don't care about vim
<gasche>
but I care about the design of programming-assistant tools
<gasche>
def-lkb_: so you want to make (something such as ocp-indent) incremental
<def-lkb_>
gasche: at least for the purupose of experimenting, yes
<gasche>
what do you mean by "syntax correction"? going farther in a parsetree with holes?
<def-lkb_>
yes
<gasche>
I haven't looked at ocp-indent closely, but I did camlp4 extensions for indentation-aware syntax for OCaml
<gasche>
and I think they use rather similar stack-based reasoning on the lexing output
<def-lkb_>
yes, it seems
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<rks`>
gasche: I never said you cared about vim :)
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<gasche>
in fact I'm mildly interested in vim
<gasche>
I nearly considered learning to use it once
<gasche>
but no time
<gasche>
(I think I would rather use the viper mode)
<rks`>
(If you do, consider evil, it's supposed to be better)
<rks`>
(I'd be curious to know how that interacts with other emacs modes/packages)
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<smondet>
rks`: i use emacs+evil, sometimes it's a bit of a pain but much better than plain emacs IMHO
<gasche>
def-lkb_: the token stream has a much simpler structure than the AST
<gasche>
if you store the location of each token, you can probably re-lex only the parts that changed
<gasche>
(start at the first one that cross the begining of the changed location, and stop at the first one that stops outside this location at the boundary of one that was lexed already)
<gasche>
as you see, it's even rather easy to preserve the end of the input, unless what Merlin does for parsing
<rks`>
gasche: from what I remember def-lkb_ did something like that when trying to have ocp-indent working
<rks`>
he didn't save the whole stream of tokens but some "meaningful" tokens (which acted as checkpoints)
<rks`>
and tried to work only on the parts that changed
<def-lkb_>
gasche: yeah, that's not a problem
<rks`>
the thing is
<rks`>
the problem is having vim tell you what changed.
<gasche>
erf
<rks`>
(and vim does a really _really_ poor job on that front)
<def-lkb_>
the problem was essentially corner-cases not being handled (say long comments)
<def-lkb_>
(and vim sucking)
<rks`>
(at the moment we have merlin [and coquille] working [kinda] by using a set of more or less ugly heuristics)