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<penryu>
I'm trying to make sure I understand the difference between these two expressions.
<penryu>
since, I think to the average C/C++ programmer, they're indistinguishable
<penryu>
let x = 5 (* this is a symbolic operation *)
<penryu>
x <- 5 (* this is an ... imperative operation? *)
<_habnabit>
yes. the latter mutates something, and the former doesn't
<penryu>
since in the first isn't an assignment, despite the =; it merely tells the interpreter/compiler that x is hereafter synonymous with the value 5
<_habnabit>
yes
<penryu>
ah. thank you.
<penryu>
even if, in the second expression, x is already the value 5, so it not mutated. it's just the intent of the operation that x is not a label or symbol representing a value, but an actual container for value(s)
<_habnabit>
I can't parse the first part of what you said, but the rest is accurate
<_habnabit>
:= does the same thing
<penryu>
ok. the second part is what mappers. the first is just disclaimer.
<penryu>
sigh.
<penryu>
*matters*
<penryu>
_habnabit: thanks.
<penryu>
I'm fascinated by ML's approach to FP, but I'm still somewhat new.
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<mrvn>
penryu: let x = 5 --> int *x = &5, x <- 5 --> *x = 5
<penryu>
I've thought of the "let x =" as more like a const or, maybe a #define is even closer to the definition.
<penryu>
I'm more trying to wrap my head around the semantic different between symbolic and imperative operations.
<mrvn>
penryu: wether it is const or not depends on what you bind. let x = "foo" in x.[0] <- 'F'
<penryu>
and I think I've mostly got it.
<mrvn>
Point is that let just gives the thing a new name
<penryu>
ok
<mrvn>
or in other words let never makes a copy.
<penryu>
ah, gotcha.
<flux>
it is basically 'const'. let x = 5 is const int x = 5, however let x = "hello" is char* const x = "hello"
<flux>
I suppose mrvn was pointing to tagging with the pointers and all, but that doesn't happen with integers
<flux>
actually I should say it's int const x = 5 to be a bit more consistent :)
<mrvn>
flux: makes no difference semantically wether ints are boxed or not.
<flux>
mrvn, well it does, when you use identity comparison operator
<flux>
but, breakfast
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<pippijn>
what is a good book on ocaml?
<pippijn>
or are books not recommended for ocaml?
<reynir_>
We don't read them book
<Qrntz>
I've read practical ocaml, but it's nowhere as good as practical CL, honestly
<reynir_>
Seriously though, Jason Hickey's book on ocaml is OK although it's still a draft
<reynir_>
(I have only read the first ~8 chapters)
<pippijn>
it's my birthday soon and I need to give some ideas.. I never have any ideas
<pippijn>
is there a book I should read if I'm interested in type theory?
<reynir_>
There's "Types and programming languages" by Benjamin Pierce. I have heard it's good
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<nico-tls>
bonjour, je "débute" en caml et j'ai un petit souci : l'utilisation de Scanf.fscanf me fait avancer la position de lecture (pos_in) de quelques 1000 caractères... normal ?
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<mrvn>
if only everyone would understand french
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<hiptobecubic>
adrien, nico-tls
<nico-tls>
hi mrvn
<nico-tls>
English is fine for me too
<nico-tls>
I am beginning with caml, and my problem is that using Scanf.fscanf move the input position (post_in) approximately 1000 characters forward
<nico-tls>
that's not very convenient as I would like to use input_byte after to read a file. so is it normal? avoidable?
<gnuvince>
nico-tls: (je parle français, donc si tu te sens plus à l'aise, te gêne pas) on peut voir ton bout de code?
<mrvn>
sure that is not just the buffering of the in_channel?
<gnuvince>
Oh, that last part was supposed to be in English; can we see your code?
<nico-tls>
here is a screenshot (128kio) with the code on the left side, toplevel on right side: http://www.izipik.com/fr/images.php?date=201204/21&img=lzwkvkhiuey9kfbudj-capture_du_2012-04-13_22_07_11.png
<nico-tls>
the use of Scanf.fscanf f "%d %d " (fun w h -> width := w; height := h); just after the "read metadata" comment moves pos_in around 1000 chars forward
<nico-tls>
line starting with (* *) are meant to print the current input position (in brackets)
<nico-tls>
penryu: which warning ? I don't see anything regarding the position
<nico-tls>
oh, I found it...
<nico-tls>
thank you mrvn and penryu
<nico-tls>
I should have read the doc more attentively
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<nico-tls>
so is there a way to use fscanf to read characters from a binary file containing integers, the same way as input_byte does?
<vext01>
anyone using ocamleditor?
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<mrvn>
nico-tls: maybe with bscanf and %r or something
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<mrvn>
gildor: ping. Could you make a release of ExtUnix please?
<zorun>
it doesn't integrate with gmail, but you can easily import/export icalendar files
<vext01>
zorun: yeh i have had my eye on that
<zorun>
and it's quite hackable :)
<vext01>
gmails was on the feaure list
<vext01>
is it implemented now?
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<zorun>
was it?
<zorun>
I doubt so
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<vext01>
once upon a time they had a wishlist
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<hiptobecubic>
wyrd looks really great
<mrvn>
I need an idea for creating a terrain map for a game. Terrain goes from Ocean to snow covered mountains in 5 steps and tiles are hexagonal. ideas?
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<hiptobecubic>
ideas for what
<thelema_>
mrvn: on how to generate?
<mrvn>
how to generate such a map that isn't just completly random tiles.
<hiptobecubic>
probabilistic function to choose tile type?
<hiptobecubic>
such that low values are ocean, high are snow mountains, etc?
<mrvn>
hiptobecubic: that puts snow capped mountains next to ocean. Should be a slope going through the terrains.
<flux>
basically it is summing n sin functions that have different phase and different weight
<hiptobecubic>
alright, I guess i give up on this build error for wyrd. ocaml's compiler errors defeat me.
<xlq>
I wrote a polymorphic function and called it, and it all went well. Then I called it from a different place, with different types, and got a type error at the original call.
<mrvn>
xlq: was it 'a or '_a?
<xlq>
It's as if the type parameters of the polymorphic function got unified, so that it was no longer polymorphic.
<xlq>
mrvn: 'a I think. What's '_a?
<mrvn>
xlq: a type that is jet to be unified
<xlq>
Well annotating the polymorphic function doesn't seem to help.
<thelema_>
xlq: what's the inferred type?
<xlq>
Of the polymorphic function? Don't know. How can I find out?
<thelema_>
to find out the type, enter it in the topleve
<thelema_>
*topvelel
<thelema_>
or compile with -annot
<thelema_>
and use emacs' C-c C-t to show the type
<thelema_>
or use ocamlc -i to print the interface
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<xlq>
I seem to have to go through dependency hell to use the top-level ("unbound module..."). Compiling with -annot produces non-human-readable files. ocamlc -i also has problems with "unbound module".
<thelema_>
# let f : 'a. ('a -> 'a) -> 'a list -> 'a list = List.map;;
<thelema_>
val f : ('a -> 'a) -> 'a list -> 'a list = <fun>
<thelema_>
# f (fun x -> x+1) [3];;
<thelema_>
- : int list = [4]
<zaltekk>
hey guys...i'm interested in learning ocaml. i checked out amazon and saw that the Practical OCaml book from 2006(the only relevant result) had horrible reviews. where should i start learning?
<pippijn>
ah 'a. makes sure a variable is actually polymorphic?
<zaltekk>
i typically look for a book to get a good introduction to a new language
<flux>
thelema_, hmm, it seems to me that I've had a misunderstanding then
<flux>
xlq, I was definitely wrong about the 'a scope as wel :)
<xlq>
It's always the simple things that go wrong >_<
<xlq>
Oh wait, no, the stuff I put in the .mli file was wrong :(
<xlq>
I still have the problem.
<Anarchos>
xlq try to erase the .mli file and compile with ocamlc -i
<xlq>
OK, so I've declared the function in the .mli and I've defined it in the .ml. It compiles.
<xlq>
But when I actually use the function in the .ml file, it complains that the implementation doesn't match the interface. When it does so, it displays the specific instantiation of the function's type in its error message.
<xlq>
Aha! I define the function in a "let rec ... and ... and ...".
<xlq>
When I move it out of that series of recursive definitions, everything works!
<xlq>
Solved. Here's a test-case. I wouldn't have expected "let rec" to make any difference to that!
<Hodapp>
I am examining http://caml.inria.fr/pub/docs/manual-ocaml/manual003.html; first they give their recursive functions for insertion sort, and they say that the function becomes polymorphic by virtue of <=, the comparison operator, being polymorphic
<Hodapp>
They discuss variants later, and give an example: 'type sign = Positive | Negative;; let sign_int n = if n >= 0 then Positive else Negative;;'
<Hodapp>
If the >= operator is polymorphic and I can't really see anything else being used in that function then why is sign_int not also polymorphic?
<xlq>
It should be.
<xlq>
Oh, no, because you compared to 0 of course.
<xlq>
(>=) is 'a -> 'a -> bool.
<xlq>
By doing n >= 0 you have bound 'a to int.
<Hodapp>
oh... wow, I should have noticed that.
<Anarchos>
Hodapp it reminds me the famous boolean type definition of D. Knuth : typedef boolean = enum {true,false, woops} :)
<Hodapp>
lol
<xlq>
haha
<Hodapp>
This whole 'a thing is looking sort of like templates in C++, only not an atrocious clusterf**k.
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<xlq>
Hodapp: That's pretty much what it is. But it's less powerful. It's not Turing-complete at compile-time, and you can't operate on polymorphic parameters without being given functions to do so.
<xlq>
But one implementation is shared with all instantiations, so there's no code bloat.
<xlq>
For example, in C++ you can write a "function" that maps from type to type. You can't do that in Caml.
<Hodapp>
xlq: When the compiler generates errors that are longer than the code and make no sense whatsoever, I'll gladly eschew the compile-time Turing completeness.
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<xlq>
Hodapp: Indeed.
<zaltekk>
but paragraph-long errors are the best :P
<Hodapp>
Maps from type to type - how do you mean?
<xlq>
Hodapp: f<int>::t x; // declares x to be of type f(int).
<Hodapp>
How would f then be used?
<xlq>
No, f(int) gets evaluated at compile-time.
<xlq>
So if you've defined f to map int to long int, then x will be of type long int.
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<Hodapp>
I feel like this is not worth the added complexity.
<xlq>
A perfectly reasonable opinion indeed!
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<rly>
I get checking for lablgtk2.sourceview2... ocamlfind: Package `lablgtk2.sourceview2' not found
<rly>
I installed lablgtk into somewhere below /usr/lib.
<Hodapp>
Any recommendation for good interactive environments? Right now I'm just using 'ocaml' itself but I might like to recall earlier lines and edit and such...
<rly>
./configure doesn't appear to give any options to set the path to look.
<rly>
This is for lablgtkextras-1.1
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<Anarchos>
Who ever used elkhound/elsa/olmar (parser from C++ to ocaml) ?
<mrvn>
A tile is a small unit. Buildings will take up many tiles.
<pippijn>
oh, okay
<pippijn>
a little different, then
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<pippijn>
I never thought I would actually use the Graphics module, but it turned out to be very useful in developing this function: http://paste.xinu.at/j8cR7f/