A little Forth-like language implemented in Clojure
For a couple of hundred lines of Clojure, Cloforth is actually pretty capable. It can do basic arithmetic, it has if statements, you can define new procedures (new 'words' in the jaron of Forth). The most interesting part is that the language is built around a compile/execute cycle: All Cloforth code, even the stuff that you type in to the REPL is compiled into an vector of functions before it is executed.
Cloforth is a stack oriented, postfix language. What this means is that numbers just get pushed onto the stack, so:
3
Will simply push 3 onto the stack, while
3 5
Will first push 3 then 5 onto the stack. The typical operators will pop a couple of numbers off of the stack, operate on them and then push the result back on, so that:
3 5 +
Will leave you with 8 on the stack.
Cloforth commands are called 'words'. So there is an 'nl' word which just prints a newline. So do this:
nl
And you will see a blank line printed. Another word is the plain old dot: . Yes, it's not much of a word, but that is the jargon. The . word justs prints whatever is on the top of the stack (popping it off in the process) Thus if you do this:
3 . nl
You will see a three followed by a newline printed.
Other handy words are dup, which pushes a copy of whatever is on top of the stack back onto the stack, so that
3 dup . nl
Will print the three and also leave it on top of the stack.
You can define your own words with : Colon takes a name and a list of words enclosed in [ ] and defines a new word. Thus this:
: plus1 [ 1 + ]
Defines a new word called 'plus1' that adds one to whatever is on the top of the stack.