Programming Erlang, 2nd Edition

Pattern Matching Again

To round off this chapter, we’ll go back to pattern matching one more time.

The following table has some examples of patterns and terms; all the variables in the patterns are assumed unbound. A term is just an Erlang data structure. The third column of the table, marked Result, shows whether the pattern matched the term and, if so, the variable bindings that were created. Read through the examples, and make sure you really understand them.

Pattern	=	Term	Result
{X,abc}	=	{123,abc}	Succeeds with X = 123
{X,Y,Z}	=	{222,def,"cat"}	Succeeds with X = 222, Y = def, and Z = "cat"
{X,Y}	=	{333,ghi,"cat"}	Fails—the tuples have different shapes
X	=	true	Succeeds with X = true
{X,Y,X}	=	{{abc,12},42,{abc,12}}	Succeeds with X = {abc,12} and Y = 42
{X,Y,X} ...