Scope

Erlang is very relaxed in its scoping rules, and does not, in many cases, abide by lexical scoping.

Joining scopes

In the case where control flow splits into several branches, if a variable is bound in all branches, the variable will be available in the outer scope as well.

joining_scope(A) ->

case A of

1 ->

B = a,

C = b;

2 ->

B = c

end,

% C is NOT in scope, it was only bound in one arm of the case clause.

% foo(C),

% B IS in scope, it was bound in both case clause arms.

foo(B).

This works on both case expressions, if expressions and receive expressions.