When encountering an if expression, the following formatting is used:

★ purty <( echo "module X where foo = if true then 0 else 1" )
module X where

foo = if true then
        0
      else
        1

However the same formatting is used when in a do block, which is a syntax error:

★ purty <( echo "module X where foo = do if true then 0 else 1" )
module X where

foo = do
    if true then
      0
    else
      1

Compile error:

Unable to parse module:
  expecting indentation past column 5 or operator