Pattern (x:pattn)

Mathematica lets us use (x_Foo) to say that something with the head Foo will be called (x). It also lets us use (x_?Test) to say something for which Test returns True will be called (x). Now if we want to say that something matching a certain pattern is called (x) we use .

The next cell gives an example where use of Pattern is helpful. Here (ff) is

only defined when it's argument is an Integer raised to a power. In addition

the exponent must have the head Plus.

In the example below we get the result of evaluating .

Next we see (ff) is undefined when it's argument isn't an Integer raised to a

power where the exponent has the head Plus.

Created by Mathematica (May 16, 2004)