Erlang Reference Manual

User's Guide

Version 12.0.2

Chapters

4 Pattern Matching

4.1  Pattern Matching

Variables are bound to values through the pattern matching mechanism. Pattern matching occurs when evaluating a function call, case- receive- try- expressions and match operator (=) expressions.

In a pattern matching, a left-hand side pattern is matched against a right-hand side term. If the matching succeeds, any unbound variables in the pattern become bound. If the matching fails, a run-time error occurs.

Examples:

1> X.
** 1:1: variable 'X' is unbound **
2> X = 2.
2
3> X + 1.
3
4> {X, Y} = {1, 2}.
** exception error: no match of right hand side value {1,2}
5> {X, Y} = {2, 3}.
{2,3}
6> Y.
3