Initial data commit

Task/Middle-three-digits/Factor/middle-three-digits.factor

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+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