Assignment

Assignment ::= Ident ":=" Expression |
	       Connection ":=" Expression

The left part of an assignment (referred to as the  LValue) can be an identifier or connection expression. The first case characterizes a situation where a variable (global or local to a procedure) receives a value, while the second one characterizes a case where the statement attaches a value to a non-terminal as an annotation.

When the lvalue is a single identifier, the following applies:

• If the lvalue can refer to several declarations (for instance, when dealing with nested quantifiers, or when a procedure declares a local which name matches a global variable's name) the closest enclosing declaration is used.
• If the lvalue denotes a read-only variable or a constant, an error message is issued.
• Since parameter passing as supported by RainCode always happens by value, aliasing cannot occur. The only way a variable can have its value changed, is by executing an assignment where the variable's name is used as lvalue.

The rules that dictate the assignment of annotation are described extensively when describing annotation.

RainCode performs no type checking with regard to the previous value of the variable. A string value can be assigned to a variable that previously denoted an integer value. Similarly, when using the assignment to annotate a non-terminal, there is no restriction regarding the type of the previous value of the annotation if any.