getProtocolByName

Sun, 3 Mar 2002 17:42:56 +0000

&nbsp;Finn,&nbsp;Thanks for this. I thought since I=
 wasn't actually using the socket module I wouldn't have to use withSockets=
Do.The documentation for BSD is a little spartan and a few explanato=
ry words about how errors get handled wouldn't go amiss.Anyway, it n=
ow works so I'll move on to the next bit.Dominic. Finn Wilcox &lt;finnw@sucs.org&gt; 03/=
03/2002 09:30 Please respond to finnw <B=
R> To: dominic.j.steinitz@britishairwa=
ys.com cc: haskell@haskell.=
org bcc: Subject:</FON=
T> Re: getProtocolByName On Sun, 3 Mar 2002 dominic.j.steinitz@britishairway=
s.com wrote: &gt; Here's my =
test program. TCP is a valid protocol. But I get the following &gt; when=
 I run it. I'm running under W98 by the way. I have two questions: &gt;<=
BR>&gt; 1) Why do I get an error? You want: &gt; module Main(main) where &gt; &gt; import BSD<=
BR> &nbsp;import Socket (withSocketsDo) &gt; &gt; main =3D &nbsp;=
 &nbsp; withSocketsDo $ &gt; &nbsp; &nbsp;do protocolEntry &lt;- getProt=
ocolByName &quot;TCP&quot; &nbsp; &nbsp; ... &gt; See <A HREF=3Dh=
ttp://www.haskell.org/ghc/docs/latest/set/socket.html#AEN14601>http://www.h=
askell.org/ghc/docs/latest/set/socket.html#AEN14601</A> <FONT=
 FACE=3D"Monospace,Courier">&gt; 2) Even if this is a valid error why doesn=
't the function tell me so that I &gt; can handle it rather than termina=
ting? &gt; It is a valid error. &nbsp;It is raising an exception whic=
h you can catch if you want. e.g. import IO (catch, isDoesNotExistError) ... &nbsp; catch (do=
 protocolEntry &lt;- getProtocolByName &quot;TCP&quot; &nbsp; &nbsp; &n=
bsp; &nbsp; &nbsp; &nbsp; putStrLn (&quot;Protocol name:&quot; ++ (protoNam=
e protocolEntry))) &nbsp; &nbsp; &nbsp; &nbsp; (\e -&gt; if isDoesNotEx=
istError e then &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;=
 &nbsp; putStrLn &quot;Error&quot; else &nbsp; &nbsp; &nbsp; &nbsp; &nb=
sp; &nbsp; &nbsp; &nbsp; &nbsp; ioError e) Finn.=