Four space indentation

[bjourne]

By default haskell-mode indents with two spaces:

main = do
  opts <- execParser optsParser

I want the indentation step to be four spaces but there is no configuration for that:

main = do
    opts <- execParser optsParser

[bernhard-herzog]

The haskell-indentation.el module has a few variables for this.
E.g. setting haskell-indentation-left-offset to 4 should achieve what
you want.

There are a few more variables like this that you might also want to
change.

[bjourne]

I tried to find information on how to customize indentation in the manual but couldn't find anything.