Re: weird escaping problem with StringPattern inside Module[]

*To*: mathgroup at smc.vnet.net*Subject*: [mg100860] Re: weird escaping problem with StringPattern inside Module[]*From*: dh <dh at metrohm.com>*Date*: Tue, 16 Jun 2009 21:52:59 -0400 (EDT)*References*: <h12ggp$edj$1@smc.vnet.net>

Hi Roger, to me, the mystery is that your rule works at all. From the manual: "Symbols that occur as pattern names in lhs are treated as local to the rule. This is true when the symbols appear on the right-hand side of /; conditions in lhs, and when the symbols appear anywhere in rhs, even inside other scoping constructs. " The problem seems to be that Mathematica does not always localize pattern variables. It does it only when it thinks it necessary. Consider: Module[{pat, var = x}, pat = "a" ~~ x_ ~~ "c" -> x ] this gives: "a" ~~ x_ ~~ "c" -> x on the other hand: Module[{pat, var = x}, pat = "a" ~~ x_ ~~ "c" -> var ] gives: "a" ~~ x$_ ~~ "c" -> x this will not work, but it makes sense. Giving the variable name in a variable, it is a good guess to assume that the user does not mean the pattern variable. I could live with this. However, unfortunately it is not consistently implemented. Consider: var = x; pat = "a" ~~ x_ ~~ "c" -> var this gives: "a" ~~ x_ ~~ "c" -> x what is inconsistent compared to the foregoing. I consider this a bug. It would be better when it would work like described in the manual. I think you should inform Wolfram about this. Maybe somebody from the group has something to say about this. Daniel divisor wrote: > Hello MathGroup: > > I am having a strange problem where my code works fine in a Notebook > session but acts strangely inside a Module[]. I presume that this is > some scoping problem that is currently beyond me. > > I know how Module[] takes local variables and adds "$nnn" or something > to the variable. It is doing a similar thing to my string pattern and > I have no idea how to "escape" this and disable this behavior. > > Any help you can provide is greatly appreciated. > > This code works as expected: > > parseVars = {abc, def}; > text0 = "the rain in spain stays mainly..."; > parsePattern = "the " ~~ abc__ ~~ " in " ~~ def__ ~~ " stays main" -> > parseVars; > Flatten@StringCases[text0, parsePattern] >> {"rain", "spain"} > Print["patt=", parsePattern] >> patt=the ~~abc__~~ in ~~def__~~ stays main->{abc,def} > > > This is the module containing the exact same logic: > > getWeather[inputStr_String] := Module[ > {parseVars, parsePattern} > , parseVars = {abc, def}; > parsePattern = "the " ~~ abc__ ~~ " in " ~~ def__ ~~ " stays main" - >> parseVars; > Print["patt=", parsePattern]; > Flatten@StringCases[inputStr, parsePattern] > ] > > This shows the symptom. Notice how the pattern vars are suffixed and > hence do not match those in the rhs of StringCases[] with the result > being all are "no match"!?!?! > > getWeather[text0] >> patt=the ~~abc$__~~ in ~~def$__~~ stays main->{abc,def} >> {abc, def} > > TIA. > > Regards.. > > Roger Williams > Franklin Laboratory >

**Follow-Ups**:**Re: weird escaping problem with StringPattern inside***From:*divisor <congruentialuminaire@yahoo.com>

**Re: Re: weird escaping problem with StringPattern inside***From:*DrMajorBob <btreat1@austin.rr.com>