USING: combinators formatting io kernel math math.parser
sequences ;
IN: rosetta-code.middle-three-digits

CONSTANT: test-values {
    123 12345 1234567 987654321 10001 -10001
    -123 -100 100 -12345 1 2 -1 -10 2002 -2002 0
}

: (middle-three) ( str -- str' )
    [ midpoint@ [ 1 - ] [ 2 + ] bi ] [ subseq ] bi ;

: too-short ( -- )
    "Number must have at least three digits." print ;

: number-even ( -- )
    "Number must have an odd number of digits." print ;

: middle-three ( n -- )
    abs number>string {
        { [ dup length 3 < ] [ drop too-short ] }
        { [ dup length even? ] [ drop number-even ] }
        [ (middle-three) print ]
    } cond ;

: main ( -- )
    test-values [ dup "%9d : " printf middle-three ] each ;

MAIN: main