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Groups > comp.soft-sys.math.mathematica > #16436

Default value in pattern matching

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Hello,

I was investigating the usage of the "a_." pattern. I understand that for some built-in functions with default value, we can do

In[] := a /. {a + b_. -> "matched"}

Out[] = "matched"

However, if I define a function myself with 

In[] := Default[myPlus] = 0;
        myPlus[0] := 0;
        a /. {a + myPlus[b_.] -> "matched"}

Out[] = a

In other words, my default value is not used in the "b_." pattern. Is there a way to get a /. {a + myPlus[b_.] -> "matched"} match in the same way as a /. {a + b_. -> "matched"}?

Otherwise I have to write separately as

In[] := a /. {a -> "matched", a + myPlus[b_] -> "matched"}

This is a lot of additional work for complicated cases.

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Default value in pattern matching Yi Wang <tririverwangyi@gmail.com> - 2014-01-18 10:04 +0000
  Re: Default value in pattern matching Yi Wang <tririverwangyi@gmail.com> - 2014-01-28 11:05 +0000

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