Line after "else do" does not indent

[ryankask]

I have haskell-indentation enabled on On Emacs 24.3.1 and a snapshot of haskell-mode from 12 May.

I'm working through Real World Haskell and I have something like:

mainloop :: Handle -> Handle -> IO ()
mainloop inh outh =
  do ineof <- hIsEOF inh
     if ineof
       then return ()
       else do
    -->inpStr <- hGetLine inh
       hPutStrLn outh (map toUpper inpStr)
       mainloop inh outh

The line that starts with inpStr will not indent despite pressing tab.

I don't know if the above is bad style or if there is a different way haskell-indentation expects, but it seems like the line should indent 2 spaces.

[gracjan]

Thanks for the report, this annoys me too.

[fice-t]

@gracjan Any update on this?

[gracjan]

Not yet.

Do we have a test documenting that this is wrong?

[gracjan]

This would be good enough:

mainloop =
  runStateT $ do
  zonk

zonk should be indented more than runStateT, isn't at this point.

[gracjan]

The long story is that in this code:

function = something $ do
  zonk

we would like zonk to be two spaces from where function starts. But in the code:

function = 
  something $ do
    zonk

we would like zonk to be two spaces from where something starts. We almost have a variable that tracks this: current-indent. Almost, because current-indent tracks where to continue current expression, so in the first example in points to where something starts, not where function starts.

At the point where zonk is the knowledge if indentation should offset from function or from something is already lost, hence the issue.

The true solution would be to untangle the two meanings of current-indent and make it always track the indentation of a logically previous line, never pointing to something inside a line.

There is also a variable called left-indent and it supposedly tracks leftmost acceptable indentation. Exact mechanics behind it elude me at this point.

[gracjan]

Did this ever work? There was some code in haskell-indentation that tried to sort out if there is more than one line between starter and indentation point and setup left-indent accordingly:

        (let* ((on-new-line (= (current-column)
                               (haskell-indentation-current-indentation)))
               (lines-between (- parse-line-number starter-line))
               (left-indent (if (<= lines-between 0)
                                left-indent
                              starter-indent)))

Following code tried to somehow use it, but experimentally it does not work.

[fice-t]

I checked out 13.10 and it seems like your zonk example above worked then, but not the else do above.

[fice-t]

@gracjan A naive git bisect led me to this commit: a0c6e49

[fice-t]

@gracjan So the current status seems to be:

A single else do currently works:

something x =
  if x > 3
  then do
    return True
  else do
    return False

This worked before a0c6e49:

function = 
  something $ do
    zonk

An else do (or then do) inside another do does not work:

something' =
  do x <- getLine
     if read x > 3
       then do
       return True
       else do
       return False

The two returns should be indented.

[fice-t]

This doesn't work either:

something x = if x > 3
              then do
  return True
              else do
  return False