How does pattern matching differ from equality comparison?

Equality comparison (== or =:=) asks a yes/no question: are these two already-known values the same? Pattern matching (=, function clauses, case) does more — it can also bind unbound variables as a side effect of a successful match, and it can check structural shape rather than a single scalar value.

5 =:= 5.              %% true, plain equality
{ok, X} = {ok, 42}.   %% match succeeds AND binds X = 42
{ok, X} = {error, _}. %% match fails (badmatch), not just "false"

Another subtlety: a failed equality check just evaluates to false, while a failed pattern match (outside a guarded context) raises a badmatch exception. That's why pattern matching is used for control flow — a mismatch is treated as an exceptional condition, not a normal boolean outcome.

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