Re: on passing arguments to a function, how to break a list into

*To*: mathgroup at smc.vnet.net*Subject*: [mg103728] Re: on passing arguments to a function, how to break a list into*From*: Hannes <HannesKessler at hushmail.com>*Date*: Sun, 4 Oct 2009 05:34:52 -0400 (EDT)*References*: <ha7hvj$5qe$1@smc.vnet.net>

On 3 Okt., 15:01, "Nasser Abbasi" <n... at 12000.org> wrote: > Suppose there is a function foo[] which returns back 2 items, say 'i' and > 'j'. They must be returned as a list ofcourse, so we have this > > foo[] := Module[{i, j}, > i = 3; > j = 7; > {i, j} > ] > > Now I have another function goo[] which accepts 2 items as input, and does > something with them, as in > > goo[i_, j_] := Module[{}, > i + j > ] > > Now I'd like to call foo[], and take its output, and pass it to directly to > goo[], but I can NOT do the following: > > goo[foo[]] > > because there is no function goo[] which accept a list defined. I could > solve this easily by making an intermediate step > > {i, j} = foo[]; (*first read into local variables*) > goo[i, j] (* then call goo[] *) > > I tried to see if it is possible to eliminate this intermediate step, as it > could be unnecessary, and see if there is a function or a trick in > Mathematica which takes a list and 'unwrap' it for the purpose of making > function calls. > > Assuming such a function or method, lets call it 'W' for now, then I would > just type > > goo[ W[foo[]] = ] > > Where W[] would take output from a function, and if it is a list, would > break it down to its sublists, so that goo[ W[foo[]] ] would be converted > to goo[ i,j ]. This W[] function would only ofcourse work in the context > of function calls, as it does not make sense to write > > W[{1,2}] and expect to get just "1,2" like this, without these being > grouped in a List[]. So this function W is means only to work in argument > passing. > > I can also solve this easily by making goo[] accepts a list, but I wanted to > avoid having to type this: > > goo[arg_List] := Module[{}, > arg[[1]] + arg[[2]] > ] > > I think writing "i+j" is more clear than writing " arg[[1]] + arg[[2]]", > that is why I am asking this question. > > I wish Mathematica has named arguments? or structs, so I could write > > goo[arg_Struct] := Module[{}, > arg.i + arg.j > ] > > Any ideas? > > Thank you, > --Nasser > > __________ Information from ESET NOD32 Antivirus, version of virus signature database 4476 (20091002) __________ > > The message was checked by ESET NOD32 Antivirus. > > http://www.eset.com Hello Nasser, you can use the Apply or @@ operator foo[] := Module[{i, j}, i = 3; j = 7; {i, j}] goo[i_, j_] := i + j goo[arg_List] := Plus @@ arg goo[Sequence @@ foo[]] goo @@ foo[] goo[foo[]] Best regards, Hannes Kessler