Made IDENTITY an optional parameter to ADD-LEXICAL-VARIABLE.
Added depenency on the AST interpreter.
Added test for BLOCK-AST and RETURN-FROM-AST.
Use the AST as the identity for lexical variables.
Made IDENTITY an optional parameter to ADD-BLOCK.
Supply the BLOCK-AST as the identity.
Define method on INTERPRET-AST specialized to BLOCK-AST.
Define method on INTERPRET-AST specialized to RETURN-FROM-AST.