Task

 verify the version/revision of your currently running (compiler/interpreter/byte-compiler/runtime environment/whatever your language uses) and exit if it is too old.
 check whether the variable "bloop" exists and whether the math-function "abs()" is available and if yes compute abs(bloop).


Extra credit

 Report the number of integer variables in global scope, and their sum.


: if-older ( n true false -- )
    [ build > ] 2dip if ; inline
 
: when-older ( n true -- )
    [ ] if-older ; inline
: unless-older ( n false -- )
    [ [ ] ] dip if-older ; inline
 
900 [ "Your version of Factor is too old." print 1 exit ] when-older