quickly add/remove Debug.Trace to a module

haskell.vim

" drop this in your ftplugin directory

nnoremap <silent> <buffer> <leader>db :call AddDebugImport()<cr>
inoremap <silent> <buffer> <leader>db <c-o>:call AddDebugImport()<cr>
nnoremap <silent> <buffer> <leader>de :call DeleteDebugImport()<cr>
inoremap <silent> <buffer> <leader>de <c-o>:call DeleteDebugImport()<cr>

" TODO: does not work well with literate Haskell or funky module indentations
function! AddDebugImport()
	let s:orig_pos = winsaveview()
	let s:dline = 0

	" step 1: try to find a suitable place to add it
	" current heuristic is to try these in order:
	" 	* below the last import
	" 	* below the module declaration
	" 	* below the last language pragma
	" 	* at the top of the file
	try
		keepjumps normal G$?\C\m^\s*import\>
	catch /E486:/
		try
			" If the first line has the module declaration and nowrapscan is
			" set, gg/module will not match. To fix this, we use \zs to start
			" the match at the 'o' of module.
			keepjumps normal gg/\C\m^\s*m\zsodule\>
/\C\m\<where\>
		catch /E486:/
			try
				keepjumps normal G$?\c\m{-# language\>
			catch /E486:/
				keepjumps normal gg
				let s:dline = -1
			endtry
		endtry
	endtry

	" step 2: add it
	let s:import_pos = winsaveview()
	if s:dline == -1
		let s:lines = ["-- TODO: delete","import Debug.Trace",""]
	else
		let s:lines = ["", "-- TODO: delete","import Debug.Trace"]
	endif
	call append(line('.') + s:dline, s:lines)

	" step 3: jump back to the original position, or three lines later if we
	" inserted the import before where the cursor was before
	call AdjustView(s:orig_pos, s:import_pos["lnum"] + s:dline, len(s:lines))
	keepjumps call winrestview(s:orig_pos)
endfunction

function! DeleteDebugImport()
	let s:orig_pos = winsaveview()
	keeppatterns 1,$s/\m^-- TODO: delete\nimport Debug.Trace\n\s*\n//eI
	keeppatterns 1,$s/\m^\s*\n-- TODO: delete\nimport Debug.Trace$//eI
	" TODO: compute the updated position properly. seems hard
	call winrestview(s:orig_pos)
endfunction