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programming - Call Functions From File Without Modifying Context (Sandbox)


Let's say I have file named test.m containing


test[arg1_] := ( Print[arg1];)

What is the best technique for calling test like test["value"] while preventing test from being added to the $ContextPath?



The following almost works except you must know function values ahead of time


Block[{$ContextPath,test}, Needs["test`"];test["test"]];

My question is: How do I generalize the call above to work with any number of functions without the user needing to input definitions manually?



Answer



As Nasser notes in a comment every Symbol has a context. You should be aware that Symbols are created during parsing. See: Local variables in Module leak into the Global context.


Alright, now that we worked out what you want here is the simplified answer:


We can perform a similar operation to BeginPackage with Block:


Block[{$ContextPath = {"runPrv`", "System`"}, $Context = "runPrv`"}, . . .]


We can combine this with Leonid's method from Is it possible to use Begin and End inside a Manipulate? to keep contexts from being fully resolved until we are ready for evaluation inside the Block. (Note that Global` Symbols are still created, as discussed above, but they will not be defined.) I believe "runPrv`" may be left out of $ContextPath in our application so long as we don't change the $Context from "runPrv`" within the Block itself. Finally we have:


SetAttributes[runPrivate, HoldAllComplete];

runPrivate[code_] :=
  With[{body = MakeBoxes @ code},
    Block[{$ContextPath = {"System`"}, $Context = "runPrv`"},
      ToExpression @ body]]

Now:


runPrivate[

  Get["test.m"];
  a = 5;
  test[a]
]


5



Global Symbols a and test remain undefined:


?a

?test


Global`a


Global`test



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