> Why call it 'extensible'? It's no more extensible than C.
Extensibility refers to the ability to extend the compiler directly in the language. Lisp supports this with macros, which are not functions and are different than macros in C because they alter the behavior of the compiler, and Forth supports this with defining words and compiling words, which behave differently from other forth words because they alter the behavior of the compiler. Compare this to a macro in C, which pre-processes the macro into more C prior to compilation rather than at the time of compilation. In this respect, both Forth and Lisp are more extensible than C because facilities to extend the language exist within the language itself.
Extensibility refers to the ability to extend the compiler directly in the language. Lisp supports this with macros, which are not functions and are different than macros in C because they alter the behavior of the compiler, and Forth supports this with defining words and compiling words, which behave differently from other forth words because they alter the behavior of the compiler. Compare this to a macro in C, which pre-processes the macro into more C prior to compilation rather than at the time of compilation. In this respect, both Forth and Lisp are more extensible than C because facilities to extend the language exist within the language itself.