Forth (concatenative) used to be pretty big, back then software was simpler and you did not need a Qt wrapper, XML parser etc. Forth was very practical for the things it was originally used for. Like that embedded control software for a telescope where the "user interface" consisted of a few buttons, as in physical buttons, no screen, no mouse, no harddisk, no network connection to worry about. In that environment Forth made a lot of sense, on a modern computer, as a tool to write a modern GUI application it makes no sense at all if you ask me.

And "declarative".. Prolog is old, back then it was usually called "logic-based programming", though.

Really, Forth and Prolog, every older guy who cares about programming knows those fellas.

And Prolog did not change the way I think about programming at all. I considered it breathtakingly clean and elegant (compared to C and Pascal).. for the few things it was good at (e.g. expert systems).. but utterly unsuitable as a general-purpose language / paradigm. I felt the same way about Standard ML (it was the dominant FP language before Haskell became big). "Wow, writing a simple input/output transformer (e.g. academic compiler) or doing some basic math is so clean and elegant with this! Everything else.. not so much."

In contrast, Forth actually changed my thinking. According to Charles Moore, Forth's creator, proper software development with Forth meant finding just the right set of words, the right vocabulary, for the problem domain. Once that was accomplished writing down the program logic became trivial. Note that in Forth functions are called "words", are usually very short, and indeed word-like. So you end up with code like "ARM 90 DEGREES ROTATE".

As I said my approach to programming was changed by the exposure to Forth. I aim to discover/define an efficient "vocabulary" for the problem domain in every language. That is not the same as designing a "domain-specific language" by the way. DSLs usually go much further, making up a syntax of their own. I do not like DSLs at all. Mostly because of the associated learning curve forced upon you by every new DSL and by the usually poor tool support.

EDIT: Removed needlessly trollish part