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Catch

  • Catch[ expr ] returns the argument of the first Throw generated in the evaluation of expr.
  • Catch[ expr , form ] returns value from the first Throw[ value , tag ] for which form matches tag.
  • Catch[ expr , form , f ] returns f [ value , tag ].
  • Catch[ expr , ... ] always returns the value of expr if no Throw was generated during the evaluation.
  • form can be any expression, and is often a pattern.
  • tag in Throw[ value , tag ] is re-evaluated every time it is compared to form.
  • See the Mathematica book: Section 2.5.9.
  • See also: Check, CheckAbort.

    Further Examples

    This function throws overflow if its argument is greater than 10.

    In[1]:=

    g[20] throws overflow, which is returned as the value of the enclosing Catch.

    In[2]:=

    Out[2]=

    In this case, overflow is not generated, and the Catch has no effect.

    In[3]:=

    Out[3]=