Types and Declarations\ There are four base types: none, bool, int, and string.\ \ Function types are denoted by their parameter types and their return type.\ \ A variable (by declaration or parameter) has the type annotating the declaration.\ \ Each function declaration should add a binding to the type environment and, after all such declarations are made, initiate type checking of the function body.\ \ A variable must be declared before use. Raise an UndeclaredVariableException with the name of the identifer if an undeclared variable is used.\ \ It is an error to redeclare a variable within the same scope. Raise a VariableRedeclarationException with the name of the identifier if a variable is redeclared.\ \ Expressions