RE: match case unused

Thanks, 
 
The exercise is not explicite said to use match but the exercise is stated as this : 
 
Rewri t e t h e not f u n ct ion  f rom  t h e previou s ch apt er in  pat t ern  m at ch in g  st y le
 
The biggest problem I have is mostly that I understand if I read about things but have struggles to use it in practice. 
 
Roelof

 
To: [email protected]
From: [email protected]
Date: Fri, 27 Feb 2015 18:10:43 +0000
Subject: Re: "ocaml_beginners"::[] match case unused














 

 



  


    
      
      
      Hi,



> I have to rewrite a not function with pattern matching.> 

>So I did this : 

> 

>let not x = 

>   match x with 

>     x -> false

>     | _ -> true ;;

> 

>but now I see this warning : Warning 11: this match case is unused.



The first match case, "x", matches everything, which is why the compiler

is rightfully telling you that the second match case will never be used.



You may have a common misunderstanding among beginners: confusing the

pattern in a "match" expression with let-bindings and/or arguments with

the same name.  Note that if you rename that first pattern to "whatever",

then the problem with the function becomes obvious:



let not x = match x with

    | whatever -> false

    | _        -> true



What you actually want is probably something like this:



let not x = match x with

    | true  -> false

    | false -> true



(As you probably realise this is a silly way to write a "not" function,

but if the exercise explicitly demands using "match", so be it).



Anyway, you seem bogged down by very "beginnery" problems.  Make sure

to read and re-read the first chapters of the book you're following

until you're 100% confident you've understood it all.



Best regards,

Dario Teixeira