tricu

A lazy functional language based on Tree Calculus
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rgb.tri (801B)

      1 !import bd2c14d6db6b69308a5252a8e839705a55d30e815f012900b094315263e08d81 *
      2 !import 7a24af56a9ce9b947cadcafd3a9da127b1507275bfac62b9fa55e27490b176dc *
      3 !export main
      4 
      5 -- Validate an RGB list using the library's canonical-byte predicate.
      6 -- Try result = main [64 128 255].
      7 -- Try changing its input to [0 256 255], then [0 1].
      8 -- Canonical encoding matters: redundant high zero bits are rejected too.
      9 -- List-shape errors are separate from invalid channels; checks short-circuit.
     10 main (t _) = "Expected a list."
     11 main [_ | (t _)] = "Expected a list."
     12 main [_ | [_ | (t _)]] = "Expected a list."
     13 main [r g b] = case and? (binaryByte? r) (and? (binaryByte? g) (binaryByte? b)) of
     14   ^true = "RGB triple accepted."
     15   _ = "A channel is not a canonical byte (0-255)."
     16 main _ = "Expected exactly three channels."