Re: Why Return[] does not work?

*To*: mathgroup at smc.vnet.net*Subject*: [mg109465] Re: Why Return[] does not work?*From*: dh <dh at metrohm.com>*Date*: Wed, 28 Apr 2010 01:59:58 -0400 (EDT)*References*: <hr6ihp$2f8$1@smc.vnet.net>

On 27.04.2010 13:41, Dims wrote: > I wrote a function to check if two lists contain equal members: > > Intersects[x_List, > y_List] := (Do[(Print["Outer step ", xi]; > Do[(Print[xi, yi]; > If[xi == yi, (Print["Returning True"]; Return[True])]), {yi, > y}]), {xi, x}]; False) > > But it returns False for interecting lists: > > In[47]:= Intersects[{a, b}, {c, a}] > During evaluation of In[47]:= Outer step a > During evaluation of In[47]:= ac > During evaluation of In[47]:= aa > During evaluation of In[47]:= Returning True > During evaluation of In[47]:= Outer step b > During evaluation of In[47]:= bc > During evaluation of In[47]:= ba > Out[47]= False > > Few questions: > > 1) why does not Return[] interrupt the loops? > 2) is there better way to implement intersection check? > > Thanks > Hi, Return does only return a single level . In your case only the inner Do loop is left. Use Throw and Catch to control how many levels to jump up. In general, try to avoid Return. Daniel -- Daniel Huber Metrohm Ltd. Oberdorfstr. 68 CH-9100 Herisau Tel. +41 71 353 8585, Fax +41 71 353 8907 E-Mail:<mailto:dh at metrohm.com> Internet:<http://www.metrohm.com>