Adds:
- ast/UserFunction AST node for user-defined functions.
- astbuilder/AvailableUserFunction: reference to a parse tree for a user function.
- The AST builder only generates ASTs for user functions that are actually referenced.
- astbuilder/UserFunctionVisitor: visits (builds an AST for) a parse tree for a user function.
- This happens after the .src or .inc file has been otherwise processed, so this class serves to hook up the correct SourceFileIdentifier to the AST.
Adds enough to build the AST nodes for the module function declarations in a .em file.
Adds:
- Function: base class for module function declarations and user functions
- FunctionParameterDeclaration: declaration for a function parameter, as well as its default value if any
- FunctionParameterList: just a holder for function parameter declarations
- ModuleFunctionDeclaration: for function declarations in .em files
- FunctionResolver: hooks up function calls to module functions or user functions
- ModuleProcessor: a visitor for processing const declarations and module function declarations (const declarations are yet to come from the main branch)
