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Data.Bits

As explained in Learn Haskell by Example

The Bits type class defines bitwise operations for Haskell types that support bit-level representation.

Data.Bits provides the Bits type class for bitwise operations on types such as Word8 and Word16. Use shift to move bits and (.|.) to combine values, especially when assembling a larger word from consecutive bytes. section 12.2.3

Combining two bytes

Convert both Word8 values to Word16 before shifting. Shifting a Word8 eight places produces 0 because the byte has no room; shifting the converted value preserves its upper-byte position. OR then inserts the second byte: shift byte1_16 8 .|. byte2_16 produces 257 for two input bytes containing 1. section 12.2.3

Listing 12.25 Parser for 16-bit words
import Data.Bits

...

anyWord16 :: Parser Word16
anyWord16 = do
  h <- fromIntegral <$> anyWord8    #1
  l <- fromIntegral <$> anyWord8    #1
  return $ shift h 8 .|. l         #2

Use anyWord16 to read two bytes, convert them with fromIntegral, shift the first eight places, and combine both with bitwise OR. section 12.2.3

Listing 12.27 A parser for binary-encoded bitmaps
p4PixelP ::
  Parser
    ( RawPixel,
      RawPixel,
      RawPixel,
      RawPixel,
      RawPixel,
      RawPixel,
      RawPixel,
      RawPixel
    )
p4PixelP = do
  w <- anyWord8           #1
  let parseBitAtIndex n =
        Single $ if testBit w n then 1 else 0    #2
  return
    ( parseBitAtIndex 7,     #3
      parseBitAtIndex 6,     #3
      parseBitAtIndex 5,     #3
      parseBitAtIndex 4,     #3
      parseBitAtIndex 3,     #3
      parseBitAtIndex 2,     #3
      parseBitAtIndex 1,     #3
      parseBitAtIndex 0      #3
    ) #3

Use testBit to inspect each position in a Word8 and turn the eight bits into bitmap pixels. section 12.2.3

How Learn Haskell by Example covers it

How deep it goes
Defines shift, (.|.), and testBit through byte-combination and bitmap-parser implementations.
Examples
Demonstrates GHCi byte shifts, a Word16 parser, and a bitmap parser using testBit.
What it assumes
Assumes familiarity with Word8, Word16, parsers, and fromIntegral while demonstrating the required bit operations.
What you can do after
Build binary parsers that assemble words from bytes or extract pixels from packed bitmap bytes.
How it connects
Connects bitwise operations with Word8, Word16, fromIntegral, binary parsing, and bitmap parsing.
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