مطابقة الأنماط وعبارات الحراسة

In Erlang = is the match operator, not assignment: it binds left-side variables to right-side values, or fails if they cannot match.

Pattern matching can destructure compound terms like tuples in a single step, pulling values straight out.

The [Head | Tail] pattern splits a list into its first element and the remaining rest.

Once a variable is bound, reusing it in a pattern matches against its value rather than rebinding it.

The underscore wildcard _ matches anything and binds nothing — use it for parts you do not care about.

Function clauses are tried top to bottom, choosing the first whose arguments match. This replaces many if/else chains.

Guards add extra conditions to a clause with when; the clause fires only if both the pattern and the guard succeed.

Guards must be side-effect-free — only comparisons, arithmetic, and type tests like is_integer or is_list are allowed.

Combine guard tests with , for AND and ; for OR.

The case expression matches a value against patterns (with optional guards) and returns the branch that fits.

Pattern matching and guards make Erlang declarative — you describe data shapes instead of branching, the same skill you will use for messages.

Test your matching knowledge.

Recap: = matches and binds, you destructure tuples and lists, and function clauses with guards replace manual branching.