Re: type and type string option

On 18/05/2016 18:34, Philippe Veber [email protected] 
[ocaml_beginners] wrote:
> Hi,
>
> the problem lies in the expression:
> ```
> try
>  Sys.getenv varname
> with Not_found -> varname ^ " not defined"
> ```
> The body of a try ... with expression (here it is `Sys.getenv 
> varname`) and the expression for each case of the `with` part should 
> have the same type. Since you're using core, `Sys.getenv` returns a 
> string option, but `varname ^ " not defined"` is of type string, hence 
> the type error.
>
> Hope this helps,
>   Philippe.

Hi Philippe,

I have changed the try ... with to a match .. with

match Sys.getenv varname with | None -> "Empty" | Some n -> n

and I can compile it but some points remain unclear for me.


First I have read the documentation of Sys:

val getenv : string -> string
Return the value associated to a variable in the process environment. 
Raise Not_found if the variable is unbound.

Then I have read too that when you want to deal with raised exception, 
you use try ... with.


So OK it doesn't work, I must use macth ... with. So in this case what 
is the point to raise an exception Not_found ?

Another point that I don't understand is :

 > Since you're using core, `Sys.getenv` returns a string option

Does that mean that like in the documentation Sys.getenv returns a 
string but when used used with the Core module it returns a string option ?


Thanks for your help.

cedlemo