f.hs

{-# LANGUAGE CPP #-}
{-

With CPP enabled:
> [foldCase_ x | x <- [0..255]]
[0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,32,32,32,32,32,32,32,32,32,32,32,32,92,120,49,48,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,32,32,32,32,32,32,32,32,32,32,32,92,120,50,48,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,32,32,32,32,32,32,32,32,32,32,32,32,92,120,51,48,49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,32,32,32,32,32,32,32,32,32,32,32,32,92,120,52,48,97,98,99,100,101,102,103,104,105,106,107,108,109,110,111,32,32,32,32,32,32,32,32,32,32,32,32,92,120,55,48,113,114,115,116,117,118,119,120,121,122,91,92,93,94,95,32,32,32,32,32,32,32,32,32,32,32,32,92,120,54,48,97,98,99,100,101,102,103,104,105,106,107,108,109,110,111,32,32,32,32,32,32,32,32,32,32,32,32,92,120,55,48,113,114,115,116,117,118,119,120,121,122,123,124,125,126,127,32,32,32,32,32,32,32,32,32,32,32,32,92,120,56,48,129,130,131,132,133,134,135]

With CPP disabled:
> [foldCase_ x | x <- [0..255]]
[0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,64,97,98,99,100,101,102,103,104,105,106,107,108,109,110,111,112,113,114,115,116,117,118,119,120,121,122,91,92,93,94,95,96,97,98,99,100,101,102,103,104,105,106,107,108,109,110,111,112,113,114,115,116,117,118,119,120,121,122,123,124,125,126,127,128,129,130,131,132,133,134,135,136,137,138,139,140,141,142,143,144,145,146,147,148,149,150,151,152,153,154,155,156,157,158,159,160,161,162,163,164,165,166,167,168,169,170,171,172,173,174,175,176,177,178,179,180,181,182,183,184,185,186,187,188,189,190,191,192,193,194,195,196,197,198,199,200,201,202,203,204,205,206,207,208,209,210,211,212,213,214,215,216,217,218,219,220,221,222,223,224,225,226,227,228,229,230,231,232,233,234,235,236,237,238,239,240,241,242,243,244,245,246,247,248,249,250,251,252,253,254,255]

 - -}
{-# LANGUAGE MagicHash #-}
import           GHC.Exts (Addr#, indexWord8OffAddr#)
import           GHC.Int (Int(..))
import           GHC.Word (Word8(..))

foldCase_ :: Word8 -> Word8
foldCase_ w = case fromIntegral w of
    I# n -> W8# (indexWord8OffAddr# table n)
  where
    table :: Addr#
    table = "\x00\x01\x02\x03\x04\x05\x06\x07\x08\x09\x0a\x0b\x0c\x0d\x0e\x0f\
            \\x10\x11\x12\x13\x14\x15\x16\x17\x18\x19\x1a\x1b\x1c\x1d\x1e\x1f\
            \\x20\x21\x22\x23\x24\x25\x26\x27\x28\x29\x2a\x2b\x2c\x2d\x2e\x2f\
            \\x30\x31\x32\x33\x34\x35\x36\x37\x38\x39\x3a\x3b\x3c\x3d\x3e\x3f\
            \\x40\x61\x62\x63\x64\x65\x66\x67\x68\x69\x6a\x6b\x6c\x6d\x6e\x6f\
            \\x70\x71\x72\x73\x74\x75\x76\x77\x78\x79\x7a\x5b\x5c\x5d\x5e\x5f\
            \\x60\x61\x62\x63\x64\x65\x66\x67\x68\x69\x6a\x6b\x6c\x6d\x6e\x6f\
            \\x70\x71\x72\x73\x74\x75\x76\x77\x78\x79\x7a\x7b\x7c\x7d\x7e\x7f\
            \\x80\x81\x82\x83\x84\x85\x86\x87\x88\x89\x8a\x8b\x8c\x8d\x8e\x8f\
            \\x90\x91\x92\x93\x94\x95\x96\x97\x98\x99\x9a\x9b\x9c\x9d\x9e\x9f\
            \\xa0\xa1\xa2\xa3\xa4\xa5\xa6\xa7\xa8\xa9\xaa\xab\xac\xad\xae\xaf\
            \\xb0\xb1\xb2\xb3\xb4\xb5\xb6\xb7\xb8\xb9\xba\xbb\xbc\xbd\xbe\xbf\
            \\xc0\xc1\xc2\xc3\xc4\xc5\xc6\xc7\xc8\xc9\xca\xcb\xcc\xcd\xce\xcf\
            \\xd0\xd1\xd2\xd3\xd4\xd5\xd6\xd7\xd8\xd9\xda\xdb\xdc\xdd\xde\xdf\
            \\xe0\xe1\xe2\xe3\xe4\xe5\xe6\xe7\xe8\xe9\xea\xeb\xec\xed\xee\xef\
            \\xf0\xf1\xf2\xf3\xf4\xf5\xf6\xf7\xf8\xf9\xfa\xfb\xfc\xfd\xfe\xff"#