Data.List: Gradually deprecate old String representation of lambda

[ujihisa]

• This is not a breaking change.
• This pull request does not change all the existing Data.List tests/documents, but works fine and documentation still makes sense.
  • I'm planning to keep working on the rest gradually.
• Next steps after this pull request:
  • Make sure all the tests and docs at Data.List follow the new rule
  • Output warning message when Vim plugins use the old way, but
    still keeps the behaviour (CHANGELOG needed)
  • Remove old behaviour after a long time (CHANGELOG needed)

[tsuyoshicho]

Good progress, LGTM.

(small changing need for description)

[tsuyoshicho]

vital.vim/doc/vital/Data/List.txt

Lines 198 to 202 in 4509690

	let xs = range(0, 9)
	echo s:L.filter(xs, function('Even'))
	" [0, 2, 4, 6, 8]
	echo s:L.filter(xs, 'v:val % 2 is 0')
	" [0, 2, 4, 6, 8]

vital.vim/doc/vital/Data/List.txt

Lines 226 to 228 in 4509690

	uniq_by(
	\ ['vim', 'Vim', 'VIM', 'emacs', 'Emacs', 'EMACS', 'gVim', 'GVIM'],
	\ 'tolower(v:val)') == ['vim', 'emacs', 'gVim']

vital.vim/doc/vital/Data/List.txt

Lines 323 to 328 in 4509690

	echo s:L.max_by(
	\ ['pineapple', 'orange', 'banana', 'apple'],
	\ 'len(v:val)')
	" pineapple
	echo s:L.max_by([20, -50, -15, 30], function('abs'))
	" -50

vital.vim/doc/vital/Data/List.txt

Lines 338 to 343 in 4509690

	echo s:L.min_by(
	\ ['pineapple', 'orange', 'banana', 'apple'],
	\ 'len(v:val)')
	" apple
	echo s:L.min_by([20, -50, -15, 30], function('abs'))
	" -15

vital.vim/doc/vital/Data/List.txt

Lines 372 to 386 in 4509690

	function! Under5(x) abort
	return a:x < 5
	endfunction
	echo s:L.span('v:val < 5', [1, 3, 5, 2])
	" [[1, 3], [5, 2]]
	echo s:L.span(function('Under5'), [1, 3, 5, 2])
	" [[1, 3], [5, 2]]
	echo s:L.span('v:val==1', [1, 2])
	" [[1], [2]]
	echo s:L.span('v:val > 3', [1, 2, 3, 4, 5])
	" [[], [1, 2, 3, 4, 5]]
	echo s:L.span('v:val < 3', [1, 2, 3, 4, 5])
	" [[1, 2], [3, 4, 5]]

filter(),uniq_by,min_by,max_by,span changed in test, but not fix document.
(suggest late sorry)

What is need change?

[ujihisa]

Yes, that's the plan at the next changes 👍