Forth has always been able to do this sort of metaprogramming- in fact this approach is how most of the language is built. Constructs and syntax like conditiona

Forth has always been able to do this sort of metaprogramming- in fact this approach is how most of the language is built. Constructs and syntax like conditionals, loops and comments are all just normal word definitions and it is easy and commonplace to extend the syntax of the language for a particular program. Forth is often described as "compiled AND interpreted" because "compiling" a program constantly swaps between interpreting pre-existing definitions and building up new definitions and allocations in memory.