Homoiconicity is a start. But the killer feature is simplicity. In Lisp, only symbols and parentheses. In prolog, only predicate head, body and atoms. This is w

Homoiconicity is a start. But the killer feature is simplicity. In Lisp, only symbols and parentheses. In prolog, only predicate head, body and atoms. This is what makes those two languages so suitable to syntactic macros, while other languages claiming homoiconicity with more syntactic irregularity make syntactic macros impractical (although certainly possible). IMO, semantic AST-level macros are certainly a better choice in non homoiconic and syntactically irregular languages.