T20113.hs:7:35: error: [GHC-55287]
    • The newtype constructor pattern
      does not have a fixed runtime representation.
      Its type is:
        a :: TYPE rep
    • In the pattern: MkY {y_fld = $sel:y_fld:MkY}
      In an equation for ‘T20113.$sel:y_fld:MkY’:
          T20113.$sel:y_fld:MkY MkY {y_fld = $sel:y_fld:MkY} = $sel:y_fld:MkY

T20113.hs:7:35: error: [GHC-55287]
    The first pattern in the equation for ‘$sel:y_fld:MkY’
    does not have a fixed runtime representation.
    Its type is:
      Y a :: TYPE rep