*       # Absolute value
        define('abs(n)') :(abs_end)
abs     abs = ~(abs = lt(n,0) -n) n :(return)
abs_end

        define('rangext(str)d1,d2') :(rangext_end)
rangext num = ('+' | '-' | '') span('0123456789')
rxt1    str ',' span(' ') = ' ' :s(rxt1)
rxt2    str num . d1 ' ' num . d2 =
+           d1 ('~,' ? *eq(abs(d2 - d1),1) '~' | ',') d2 :s(rxt2)
rxt3    str ('~' | '-') num '~' = '-' :s(rxt3)
rxt4    str '~' = ',' :s(rxt4)
        rangext = str :(return)
rangext_end

*       # Test and display
        test =  '0,  1,  2,  4,  6,  7,  8, 11, 12, 14, '
+              '15, 16, 17, 18, 19, 20, 21, 22, 23, 24, '
+              '25, 27, 28, 29, 30, 31, 32, 33, 35, 36, '
+              '37, 38, 39'
        output = rangext(test)
end