Locals Lines are lines in a defined function or operator that serve only to define local names.
A Locals Line may appear anywhere between line [0] and the first executable statement in the function or operator. Locals lines may be interspersed with blank lines and comments. A Locals Line is identified by starting with a semicolon, prefixed optionally by whitespace. It may contain a comment at the end.
A Locals Line must be of the form ;name;name;name where name is any valid APL name or localisable system variable. The names are localised on entry to the function exactly as if they were specified as locals on line [0].
∇ r←foo y;a;b ⍝ some locals
;c;d ⍝ some more locals
(a b c d)←y
r←a+b-c×d
∇
The function foo shown above localises names a, b, c and d (the indentation on line [1] in this example is entirely optional)
Syntactical errors on Locals Lines are detected when the user attempts to fix the function using the Editor or ⎕FX and will causes the operation to fail.