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Recursion

Usually the name of a definition is not visible in the definition; but earlier definitions are usually visible:

1 0 / . \ "Floating-point unidentified fault" in Gforth on most platforms
: / ( n1 n2 -- n )
  dup 0= if
    -10 throw \ report division by zero
  endif
  /           \ old version
;
1 0 /

For recursive definitions you can use recursive (non-standard) or recurse:

: fac1 ( n -- n! ) recursive
 dup 0> if
   dup 1- fac1 *
 else
   drop 1
 endif ;
7 fac1 .

: fac2 ( n -- n! )
 dup 0> if
   dup 1- recurse *
 else
   drop 1
 endif ;
8 fac2 .

Assignment:

Write a recursive definition for computing the nth Fibonacci number.

Reference (including indirect recursion): See Calls and returns.