f::args="`1` is not a prorper table.";





In this code I want to ListPlot only proprly defined tables. If I run f[g[[2;;,{1,2}]]] this gives expected plot. But if I by mistake type f[g[[2;;{1,2}]]] this gives error message from Part and also my message from f, but I want in this error case to see only message from f and no messages from Mathematica functions. How to make f to behave this way?



1 Answer 1


Let's assume you have a good reason to for HoldAll attribute even though your example does not need it.

Before I answer let's take a look at your code:

  • you don't need to use ReleaseHold because there is no explicit Hold there, the argument is held and using Condition or PatternTest will result it being evaluated anyway.

  • ListQ should return True or False so ! ListQ[...] is more idiomatic than ListQ[..]===False]

So your original example can be rewritten as:

f[tab_ /; !ListQ[tab] ]:=Message[f::args, HoldForm@tab]

Now, if you want to suppress other messages you can use Quiet. Those messages are issued when you are checking the condition so you can do:

 f[tab_ /; Quiet[!ListQ[tab]] ]:=Message[f::args, HoldForm@tab]
  • $\begingroup$ Thanks for the answer! Actually I have a function of two arguments (two tables, or lists) that I want to ListPlot. The function's body is Manipulate with InputFields for the input arguments, and other controls (ranges, labels, grids etc.). One possibility is using InputField[..., String] and then ToExpression@ in ListPlot. I decided to try another idea of using HoldAll to suppress evaluation arguments in corresponding InputFields. So then I need ReleaseHold inside Manipulate, and I used this in my simple exmaple. Your suggestion works well, thank you! $\endgroup$
    – Alx
    Jul 16, 2019 at 13:37
  • $\begingroup$ But now I don't get how to make smth like this for checking arguments of InputField. If one dcides to edit initial tables from function input (in InputField) and makes this kind of typo--- one gets myriad error messages from Mathematica ... $\endgroup$
    – Alx
    Jul 16, 2019 at 13:41
  • $\begingroup$ Well, I can add Enabled->False to InputField to prevent erroneous editing. $\endgroup$
    – Alx
    Jul 16, 2019 at 14:23
  • $\begingroup$ @Sam_1q I find it hard to grasp your problem only from this description but I've seen your next question so let me take a look. $\endgroup$
    – Kuba
    Jul 17, 2019 at 6:26

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