Ocaml offers pattern matching on arrays, but it doesn't seem to behave
like list pattern-matching.

For instance, the following, where 'x' is the first element and '_' is
the rest of the array doesn't work:
# match [|1;2;3|] with [|x;_|] -> x;;

Characters 0-33:

match [|1;2;3|] with [|x;_|] -> x;;

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Warning P: this pattern-matching is not exhaustive.

Here is an example of a value that is not matched:

[| |]

Exception: Match_failure ("", 100, -408).

Is there some way to do this in Ocaml?
-deech

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--- In ocaml_beginners <at> yahoogroups.com, "ben.aurel" <ben.aurel <at> ...> wrote:
>
> hi
> I make another attempt with ocaml and it seems like it doesn't fit my
> brain yet.
>
> ---
> let max a b =
> if a > b then a else b
> ;;
>
> print_newline (max 3 5) ;;
>
> ---
>
> The error message is the following:
> This expression has type int but is here used with type unit
>
>
> If tried several things like 'int max' or casting like 'then int a',
> but it doesn't work.
>
> What am I doing wrong here?
> thanks
> ben
>

you miss the case when a = b

let max a b =
if a <= b then b else a;;

print_int (max 3 5);;

piseth kem

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--- In ocaml_beginners <at> yahoogroups.com, "murray2004eisenberg"
<murray <at> ...> wrote:
>
> How do I quit/exit/end an interactive Objective Caml session? I don't
> see this mentioned in the getting started docs.
>

#quit;;
or

exit 0; (* for return 0, same as unix command : true *)
exit 1; (* same as unix command : false *)

(* exit can be used in both interpreter and *.ml code *)

or

^D (Control + D) to send EOF to the interpreter.

---------
pisethkem

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Howdy,

bash-3.2$ ocaml
Objective Caml version 3.10.2

# exit 1;;
bash-3.2$ echo $?
1
bash-3.2$ ocaml
Objective Caml version 3.10.2

# exit 50;;
bash-3.2$ echo $?
50

The $? variable is the value that the terminated process returned.

DSL

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--- In ocaml_beginners <at> yahoogroups.com, "murray2004eisenberg"
<murray <at> ...> wrote:
>
> How do I quit/exit/end an interactive Objective Caml session? I don't
> see this mentioned in the getting started docs.
>

Use the exit method. In the toplevel type:
# exit 1;;

I am not sure what the number after 'exit' does. The exit function is
defined as:
# exit ;;
- : int -> 'a = <fun>

-deech

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Hi,

Thanks for the reply. In the meantime I managed to track down
the problem. Remember that I was using ocamlmklib to automate
the generation of the libraries:

blahcaml.cma: blahtex_stubs.o blahcaml.cmo
ocamlmklib -verbose -o blahcaml -oc blahcaml -cclib -lstdc++ $+

These are the actions taken by ocamlmklib:

+ gcc -shared -o ./dllblahcaml.so blahtex_stubs.o -L/home/dario/.godi/lib -Wl,-rpath,/home/dario/.godi/lib
+ ar rc ./libblahcaml.a blahtex_stubs.o; ranlib ./libblahcaml.a
+ ocamlc -a -o blahcaml.cma blahcaml.cmo -dllib -lblahcaml -cclib -lblahcaml -ccopt -L/home/dario/.godi/lib -ccopt -Wl,-rpath,/home/dario/.godi/lib -cclib -lstdc++

The problem is that ocamlmklib does not pass the -cclib -lstdc++
parameters to the first invocation of gcc. When I do it manually
then everything works. I'm filing this as a bug.

On a side note: how is the path /home/dario/.godi/lib obtained?
Sure, I can run `ocamlc -where` and remove the last two directories,
but I'm guessing there's a cleaner way, right?

Cheers,
Dario

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> In both cases, the reason is that exhaustiveness checking is based
> only on the type of the expression, not on its value.

Is it correct to explain let-binding for this syntax

let <pattern> = <expression1> in <expression2>

as the type inference mechanism computes type T1 of <pattern> and type
T2 of <expression1> inferring the type of variables in <pattern> using
T2, and then T1 must be the same as T2?

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>
> The warning tells you that your constants are from types with
multiple values.
> The value "()" of the type "unit" is the only value of that type so
the
> pattern "()" is exhaustive (matches the only value of that type).
In
> contrast, the type "int" contains more values than just "0", so the
> pattern "0" is not exhaustive.
>
> However, constants are just a special case of this. Any patterns
that cover
> all of the values of a type will satisfy OCaml even if they do not
contain
> any identifiers to be bound:
>
> [] | _::_
>
> None | Some _
>
> let ignore _ = ()
>
> and so on.

The value of g() is []. Why doesn't [] match g()?

> > Here is an example of a value that is not matched:
> > _::_
> > let [] = g();;
> > ^^

The value of h() is 0. Why doesn't 0 match h()?

> > Here is an example of a value that is not matched:
> > 1
> > let 0 = h();;
> > ^

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Thanks very much.
I'm studying OcamlP3L system and in its source there is a large use of Obj.magic, so I wanted to know something deeper about it.

Bye,
nicoletta
--- Mar 18/11/08, Dario Teixeira <darioteixeira <at> yahoo.com> ha scritto:
Da: Dario Teixeira <darioteixeira <at> yahoo.com>
Oggetto: Re: "ocaml_beginners"::[] Obj.magic
A: ocaml_beginners <at> yahoogroups.com
Data: Martedì 18 novembre 2008, 16:25

Hi,

> I can't find exhaustive documentation about this

> function. Could somebody explain me its specification?

The first rule of Obj.magic is that you do not talk about

Obj.magic... On a more serious note, Obj.magic is used to

"magically" overrule the type system, allowing you to do

a low-level cast of a type into another. As an example,

try this code in the top-level:

let foo : float = Obj.magic 1;;

Note that this is not a safe type-casting. In fact, on my

machine the above example causes a segfault.

While gurus can certainly find situations where Obj.magic is

indeed useful, I reckon it's almost certain that if you think

you might need Obj.magic, then there must be something wrong

with your design or you are trying to do things which are not

possible within the Ocaml type system.

Cheers,

Dario Teixeira











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Hello,
I am very new to Ocaml, this is my first day, and I wanted to know
if it is possible to prove correctness of a multi-threaded application
written in Ocaml.
Basically, I want to check that a multi-threaded implementation of an
algorithm that detects cycles in a dynamically changing graph, actually
detects the cycles. Also, the algorithm prevents previously detected
cycles from happening by not allowing certain edges to be added. And I
want to check that this property also holds.

Thank you and I hope you can help me,
Silviu ANDRICA.

[Non-text portions of this message have been removed]

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Hi all,
Is it possible to convert from a Bison parser spec to Ocaml?

thanks ...
-deech

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