Pattern Matching

## 3 Pattern Matching

### 3.1 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 lefthand side pattern is matched against a righthand 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: variable 'X' is unbound **
    2> X = 2.
    2
    3> X + 1.
    3
    4> {X, Y} = {1, 2}.
    ** exited: {{badmatch,{1,2}},...} **
    5> {X, Y} = {2, 3}.
    {2,3}
    6> Y.
    3

Copyright © 1991-2006 Ericsson AB