file:read_line - conflicting return values' syntax - no case clause matching eof exception

[Kay Kay-2-3]

As per the documentation here -

http://ftp.sunet.se/pub/lang/erlang/doc/man/file.html#read_line-1  ,
the syntax reads as -

read_line(IoDevice) -> {ok, Data} | eof | {error, Reason}

Given the ambiguity in the return values of the function , I am unsure
how to handle it.



do_read_file(IoDevice, InData, Accum) ->
   case file:read_line(IoDevice) of
     {'ok', Data}  ->
       do_read_file(IoDevice, Data, lists:append(Accum, InData));
     { 'eof' } ->
       Accum
    end.


I wrote this function to use the same, but I am getting - "** exception
error: no case clause matching eof" .

What is the best way to handle the same ?

[Michael McDaniel-4]

On Sun, Feb 14, 2010 at 11:59:31PM -0800, Kay Kay wrote:

> As per the documentation here -
>
> http://ftp.sunet.se/pub/lang/erlang/doc/man/file.html#read_line-1  ,
> the syntax reads as -
>
> read_line(IoDevice) -> {ok, Data} | eof | {error, Reason}
>
> Given the ambiguity in the return values of the function , I am unsure  
> how to handle it.
>
>
>
> do_read_file(IoDevice, InData, Accum) ->
>   case file:read_line(IoDevice) of
>     {'ok', Data}  ->
>       do_read_file(IoDevice, Data, lists:append(Accum, InData));
>     { 'eof' } ->
>       Accum
>    end.
>
>
> I wrote this function to use the same, but I am getting - "** exception  
> error: no case clause matching eof" .
>
> What is the best way to handle the same ?

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

 Note that eof is not a tuple (which is the general case when using
 a single atom), so check the single atom eof in a clause

 case ...

  {ok, Data}   -> ...

  eof          -> ...

  {error, Err} -> ...

 end

~M



>
>

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[Kostis Sagonas-2]

Kay Kay wrote:
> As per the documentation here -
>
> http://ftp.sunet.se/pub/lang/erlang/doc/man/file.html#read_line-1  ,
> the syntax reads as -
>
> read_line(IoDevice) -> {ok, Data} | eof | {error, Reason}
>
> Given the ambiguity in the return values of the function , I am unsure
> how to handle it.

Ambiguity?  Which ambiguity?

The return values {ok, Data} and {error, Reason} are pairs (2-tuples)
which are distinguished by a different atom in the 1st position.  The
third return value is an *atom*.  Do not wrap it in { } and make it a
one-element tuple instead...

Kostis

> do_read_file(IoDevice, InData, Accum) ->
>   case file:read_line(IoDevice) of
>     {'ok', Data}  ->
>       do_read_file(IoDevice, Data, lists:append(Accum, InData));
>     { 'eof' } ->
>       Accum
>    end.
>
>
> I wrote this function to use the same, but I am getting - "** exception
> error: no case clause matching eof" .
>
> What is the best way to handle the same ?

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See http://www.erlang.org/faq.html
To unsubscribe; mailto:[hidden email]

[Richard O'Keefe]

On Feb 15, 2010, at 8:59 PM, Kay Kay wrote:

> As per the documentation here -
>
> http://ftp.sunet.se/pub/lang/erlang/doc/man/file.html#read_line-1  ,
> the syntax reads as -
>
> read_line(IoDevice) -> {ok, Data} | eof | {error, Reason}
>
> Given the ambiguity in the return values of the function , I am  
> unsure how to handle it.
>

What ambiguity?
All goes well: you get {ok,Data}.
Normal end of file: you get eof.
Some problem: you get {error,Reason}.

>
>
> do_read_file(IoDevice, InData, Accum) ->
>  case file:read_line(IoDevice) of
>    {'ok', Data}  ->
>      do_read_file(IoDevice, Data, lists:append(Accum, InData));
>    { 'eof' } ->
     ---------

The description says eof, not {eof}.

>
>      Accum
>   end.
>
>
> I wrote this function to use the same, but I am getting - "**  
> exception error: no case clause matching eof" .
>
> What is the best way to handle the same ?

By writing a pattern that matches eof, not {eof}.

>
>
>


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