RE: Re: A riddle: Functions that return unevaluated when they cannot
- To: mathgroup at smc.vnet.net
- Subject: [mg82777] RE: [mg82716] Re: A riddle: Functions that return unevaluated when they cannot
- From: "Ingolf Dahl" <ingolf.dahl at telia.com>
- Date: Tue, 30 Oct 2007 05:50:21 -0500 (EST)
- References: <ff9sin$5vc$1@smc.vnet.net> <ffckoe$sop$1@smc.vnet.net> <ffed3p$bg7$1@smc.vnet.net> <ffhqss$4mr$1@smc.vnet.net> <fg4d62$681$1@smc.vnet.net> <200710300816.DAA12863@smc.vnet.net>
But it is documented in the doc page for Condition. Look beneath "Scope"! There I can read "Share a variable between a condition and function body: In[1]:= f[x_] := Module[{u}, u^2 /; ((u = x - 1) > 0)] In[2]:= f[0] Out[2]= f[0] In[3]:= f[6] Out[3]= 25" I must confess I do not really understand the use of the concept "Scope" here. Best regards Ingolf Dahl > -----Original Message----- > From: Albert [mailto:awnl at arcor.net] > Sent: den 30 oktober 2007 09:16 > To: mathgroup at smc.vnet.net > Subject: [mg82716] Re: A riddle: Functions that return > unevaluated when they cannot > > Szabolcs Horv=C3=A1t wrote: > > Albert wrote: > >> Hi, > >> > >> Is this what you are looking for? > > > > Yes, it it. Thank you! My newsreader has misplaced your > message, so > > I= > > > did not notice it until now. > > > > A function like > > g[x_] := Module[{res}, Pause[3]; res = x + 2; res /; res < 10] > > reproduces the timing behaviour of Integrate[] et al. :-) > I was not > > familiar with this use of /; (it is described in the doc page of > > Module= > , > > not in the doc page of Condition) > > ah, now I know that it is at least documented somewhere, also > to my understanding it is not clear from the docpage (and > also not from the examples or the old documentation in > version 5) what exactly it does. > Strange. But well, it works and seems to stay there... And for > completeness: With and Block have the same part in their docpages. > > albert > > >
- References:
- Re: A riddle: Functions that return unevaluated when they cannot
- From: Albert <awnl@arcor.net>
- Re: A riddle: Functions that return unevaluated when they cannot