# RFC: Add pattern synonyms to base

Since we have pattern synonyms it's worth considering if some belong in base:

Data.Complex.Lens contains patterns that could be defined in base, here are some more suggestions:

### Data.Array

```
pattern ArrayIx :: Ix i => (i, i) -> [(i, e)] -> Array i e
pattern ArrayIx low'high xs <- ((\arr -> (bounds arr, assocs arr)) -> (low'high, xs))
where ArrayIx low'high xs = array low'high xs
```

### Data.Bits

```
pattern ZeroBits :: (Eq a, Bits a) => a
pattern ZeroBits <- ((== zeroBits) -> True)
where ZeroBits = zeroBits
pattern BitSize :: Bits a => Int -> a
pattern BitSize n <- (bitSizeMaybe -> Just n)
pattern Signed :: Bits a => a
pattern Signed <- (isSigned -> True)
pattern Unsigned :: Bits a => a
pattern Unsigned <- (isSigned -> False)
pattern PopCount :: Bits a => Int -> a
pattern PopCount n <- (popCount -> n)
```

### Data.Char

```
pattern ControlChar :: Char
pattern ControlChar <- (isControl -> True)
pattern SpaceChar :: Char
pattern SpaceChar <- (isSpace -> True)
```

### Data.Complex

```
import Data.Complex (Complex, conjugate, polar, mkPolar)
import qualified Data.Complex as C
pattern Conjugate :: Num a => Complex a -> Complex a
pattern Conjugate a <- (conjugate -> a)
where Conjugate a = conjugate a
pattern Polar :: RealFloat a => a -> a -> Complex a
pattern Polar m theta <- (polar -> (m, theta))
where Polar m theta = mkPolar m theta
-- See https://github.com/ekmett/lens/issues/653
pattern Real :: Num a => a -> Complex a
pattern Real r <- r C.:+ _
where Real r = r C.:+ 0
pattern Imaginary :: Num a => a -> Complex a
pattern Imaginary i <- _ C.:+ i
where Imaginary i = 0 C.:+ i
pattern (:+) :: a -> a -> Complex a
pattern (:+) { realPart, imagPart } = realPart C.:+ imagPart
```

### GHC.Float

```
pattern NegativeZero :: RealFloat a => a
pattern NegativeZero <- (isNegativeZero -> True)
where NegativeZero = -0
pattern Denormalized :: RealFloat a => a
pattern Denormalized <- (isDenormalized -> True)
pattern NaN :: RealFloat a => a
pattern NaN <- (isNaN -> True)
where NaN = 0 / 0
-- How ever negative infinity is handled
pattern Infinity :: RealFloat a => a
pattern Infinity <- (isInfinite -> True)
where Infinity = 1 / 0
```

### Foreign.Ptr

```
pattern NullPtr :: Ptr a
pattern NullPtr <- ((==) nullPtr -> True)
where NullPtr = nullPtr
```

Used here