Mathematica 9 is now available
THIS IS DOCUMENTATION FOR AN OBSOLETE PRODUCT.
SEE THE DOCUMENTATION CENTER FOR THE LATEST INFORMATION.
Wolfram Mathematica Documentation Center
DOCUMENTATION CENTER SEARCH
New to Mathematica? Find your learning path »
Virtual Book > Core Language > Patterns > Patterns Involving Alternatives >
MATHEMATICA TUTORIAL
|Related Tutorials »

Patterns Involving Alternatives

patt1|patt2|...a pattern that can have one of several forms

Specifying patterns that involve alternatives.

This defines to give when its argument is either or .
In[1]:=
Click for copyable input
The first two cases give .
In[2]:=
Click for copyable input
Out[2]=
You can also use alternatives in transformation rules.
In[3]:=
Click for copyable input
Out[3]=
Here is another example, in which one of the alternatives is itself a pattern.
In[4]:=
Click for copyable input
Out[4]=
When you use alternatives in patterns, you should make sure that the same set of names appear in each alternative. When a pattern like matches an expression, there will always be a definite expression that corresponds to the object . If you try to match a pattern like , then there still will be definite expressions corresponding to and , but the unmatched one will be Sequence.
Here is used to name the head, which can be either or .
In[5]:=
Click for copyable input
Out[5]=
Ask a question about this page  |  Suggest an improvement  |  Leave a message for the team
Format:   HTML  |  CDF