Variables
Variables may only contain lower case letters and underscores. They are assigned using the colon (:) operator. The value is left on the stack after the assignment has occurred.
aya> 1 :a
1
aya> 3:b a +
4
Variable Scope
A new scope is introduced if a block contains any variable declaration in its header. When a variable assignment occurs, the interpreter will walk outward until a reference to that variable appears. If it does not appear in any of the scopes before the global scope, a new reference will be created there. In order to ensure a variable is using local scope, the variable name must be included in the block header. If a block does not contain a header, a new scope will not be introduced. These concepts are best demonstrated by example.
Let us introduce the variables a and b:
"A":a; "B":b;
When blocks have arguments, a scope is introduced for that variable.
Here, the number zero is assigned to b within the scope of the
block. When the block ends, the scope is destroyed and we reference the
now global variable b.
aya> 0 {b, b.P}~ b.P
0B
Local variables also create local scopes for that variable. Here, we
create a local scope for the variable b. a is not included in
the new scope.
aya> .# Local variable b declared in header
{:b,
0:a;
1:b;
"a = $a," .P
"b = $b\n" .P
}~
"a = $a," .P
"a = $b\n" .P
a = 0,b = 1
a = 0,a = B