Explain concatenative languages to me like I'm an 8-year-old

Question

I\'ve read the Wikipedia article on concatenative languages, and I am now more confused than I was when I started. :-)

What is a concatenative language in stupid people

Answer 1

My pragmatic (and subjective) definition for concatenative programming (now, you can avoid read the rest of it):

-> function composition in extreme ways (with Reverse Polish notation (RPN) syntax):

( Forth code )
: fib
  dup 2 <= if
    drop 1
  else
    dup 1 - recurse
    swap 2 - recurse +
  then ;

-> everything is a function, or at least, can be a function:

( Forth code )
: 1 1 ; \ define a function 1 to push the literal number 1 on stack

-> arguments are passed implicitly over functions (ok, it seems to be a definition for tacit-programming), but, this in Forth:

a b c

may be in Lisp:

(c a b)
(c (b a))
(c (b (a)))

so, it's easy to generate ambiguous code... you can write definitions that push the xt (execution token) on stack and define a small alias for 'execute':

( Forth code )
: <- execute ; \ apply function

so, you'll get:

a b c <- \ Lisp: (c a b)
a b <- c <- \ Lisp: (c (b a))
a <- b <- c <- \ Lisp: (c (b (a)))