question about expression mappings

[Christian Brabandt]

Hi,
I think I found an inconsistency.

#v+
vim -u NONE -N
:let @a='foobar'
:fu AB()
return "<c-r>a"
:endfu
:fu CD()
return "\<c-r>a"
:endfu
:imap <expr> ab '<c-r>a'
:imap <expr> cd AB()
:imap <expr> ef CD()
#v-
Now enter insert mode:

1) Inserting ab results in:
foobar
2) Inserting cd results in:
<c-r>a
3) Inserting ef results in:
foobar

That is unexpected. I think the first case, it should also insert
'<c-r>a' Since according to the documentation (:h expr-quote) keys need
to be returned like "\<key>" in a double quoted string.

How would one return the literal string "<c-r>a" in the first case?
Is this a bug or did I miss anything?

Best,
Christian
--
Alles Gute kommt nach oben.

[Nikolay Aleksandrovich Pavlov]

​You miss how maps are parsed. When filling mappings table (i.e. at the time :*map commands are parsed themselves) rhs always has special keys translated, regardless whether it is <expr> or not.​ And only then, when you type something, this is treated as expression. This way allows `:inoremap <expr> foo <SID>Func()` to work: `<SID>` must be translated before mapping is run because mapping is run in the currently effective script context and not in the context of the script it was defined in (unlike :command does).

To have literal string you need to escape `<` just as you will do in case of other mappings: `'<LT>c-r>a'`. Or you may abstract this away in a function or global variable.

 

Best,
Christian
--
Alles Gute kommt nach oben.

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[Christian Brabandt]

Hi Nikolay!

Ah thanks. I think this should be documented.

Best,
Christian
--
Was eine Nation groß macht, sind nicht in erster Linie die großen
Männer. Es ist das Format der Mittelmäßigen.
-- José Ortega y Gasset