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MathGroup Archive 1999

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RE: Early out with Map?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg16041] RE: [mg16036] Early out with Map?
  • From: "Jean-Marie THOMAS" <jmthomas at agat.net>
  • Date: Sun, 21 Feb 1999 00:15:17 -0500
  • Sender: owner-wri-mathgroup at wolfram.com

You can use Catch and Throw:
myList=Range[10]
myFunction:=If[#===7,Throw["out"]]&
Catch[myFunction/@myList]

Tracing Catch[myFunction/@myList] will show you myFunction is not evaluated
for arguments after 7.

Hope this helps,


****************************************
Jean-Marie THOMAS
mailto:jmthomas at agat.net
Conseil et Audit en Ingenierie de Calcul
Strasbourg, France
http://www.agat.net
****************************************

-----Original Message-----
From: Oscar Stiffelman [mailto:ostiffel at leland.stanford.edu]
To: mathgroup at smc.vnet.net
Subject: [mg16041] [mg16036] Early out with Map?


Hi,

Is it possible to interrupt Map before it reaches then end of the list?


For example, how would I convert the following from procedural to
functional?


(* This is the procedural version *)
foundSolution = False;
For[i =1, i <= numChildren && ! foundSolution, i++,
    If[testChild[children[[i]]],
        foundSolution = True;
      ];
];
foundSolution



(*
* This keeps going until it reaches the end of the list.
* I would prefer to return as soon as testChild returns True
*)
Or @@ Map[testChild, children]


(*
* This does not actually return
*)
Map[If[testChild[#], Return[True], False]&, children]




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