I am introducing the mathematica Security (MSP module) to our system. The Document suggests use MSPToExpression as followed:



$$var = "5+7";

MSPToExpression[ $$var] (*the output is 12*)

But when I tried to adapt this function to $PrePrint with scripts:

$PrePrint = With[{$$var = ToString[#, InputForm]}, MSPToExpression[$$var]] &;

$PrePrint = With[{expr = #}, MSPToExpression[expr]] &;

$PrePrint = With[{$$var = #}, MSPToExpression[$$var]] &;

Input: 5+7

there's same error says: enter image description here

It can't recognize $$var as symbol, can anyone help me on this? Many thanks! :)

  • $\begingroup$ What if you use Module? With injects expressions to held slots. $\endgroup$
    – Kuba
    Commented Nov 27, 2015 at 7:49
  • $\begingroup$ @Kuba Hi, Could you please paste the full script ? I am a real newbee for mathematica. $\endgroup$
    – Michael
    Commented Nov 27, 2015 at 7:57

1 Answer 1


I suppose this is what you need.

So the first thing is to use Module since With injects values into held expressions.

Moreover PrePrint is probably to late to catch "5+7". So I'd go with $Pre:

$Pre = Function[expr, 
        {expr$ = ToString[Unevaluated[expr], InputForm]},
  • $\begingroup$ Thanks! It works well. it's what I was looking for . $\endgroup$
    – Michael
    Commented Nov 27, 2015 at 8:29
  • 1
    $\begingroup$ Watch out when using HoldAll instead of HoldAllComplete in such functions! Evaluate[5 + 7] then evaluates to MSPToExpression["12"] $\endgroup$ Commented Nov 27, 2015 at 11:33
  • $\begingroup$ @JacobAkkerboom good point. $\endgroup$
    – Kuba
    Commented Nov 27, 2015 at 11:57

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