:lua io.write() default input/output

[zgpio]

• nvim --version: NVIM v0.4.0-1447-gfe2ada737
• vim -u DEFAULTS (version: ) behaves differently? yes
• Operating system/version: macos 10.14
• Terminal name/version: mac terminal

Steps to reproduce using nvim -u NORC

1. nvim -u NONE
2. :lua io.write('aaaa')
   Show as follow:
   

Actual behaviour

cmd line mess up

Expected behaviour

[justinmk]

It writes to stdout. What do you expect?

Use :lua print() if you want :echo-like behavior.

[zgpio]

Sorry, I got it.

[bfredl]

maybe we should disable the default input and output file of the io. module. These are not hardwired to be stdin/stdout, this is just the initial state of the module (and expected to be changed). Plugins can still use io.stdout if they have a good reason.

[luiz00martins]

I came across the same problem while trying to use io.write to print some text without a newline (which is what is recommended in the official lua site).

@justinmk Is there a way to use print without outputting a linefeed?

[lewis6991]

Luajit also recommends using io.write over print():

print() is not compiled, use io.write().

Would it not be possible to make io.print() output to the same place print() does?

[gpanders]

print() is compiled in Nvim https://github.com/neovim/neovim/blob/master/src/nvim/lua/executor.c#L412-L413

Is there a way to use print without outputting a linefeed?

I'm curious: considering print writes to the Nvim message area, what would omitting a linefeed even look like?

Would it not be possible to make io.print() output to the same place print() does?

This is possible and would actually be easy, but it would change the semantics of io.write (since writing to the message area always adds a newline). But I'm beginning to get out of my depth here, I'll wait for bfredl to come in and set me straight.

[luiz00martins]

I'm curious: considering print writes to the Nvim message area, what would omitting a linefeed even look like?

I don't actually intend to use it to echo things. My objective was to use it in an expr mapping, since using execute('lua <...>') doesn't seem to work with returned values from lua, only printed ones. However, values printed with print always come with an extra linefeed at the end, messing up the mapping.