Advice needed for a Lua <-> Vim bridge library

[Rob Hoelz <rob@...>]

Hello everyone,

I'm currently working on a better bridge between Lua and Vim to make it
easier to write Vim plugins in Lua.  However, during my implementation
of this, I've hit a bit of a snag and was hoping for some insight from
other Lua users.

Vimscript uses prefixes to address different variable scopes; for
example, to set the 'foo' variable for the current window, I'd do this:

  let w:foo = 17

My plugin exposes this feature in a very Lua-esque manner:

  w.foo = 17

Until now, it has only worked with numbers, strings, and nil.  One of
the next things I plan on doing with this plugin is adding support for
assigning booleans.  Vimscript, however, doesn't have the notion of
boolean; 0 is false and all other values are true (I think).  When it
comes to simple assignment, this is trivial; just convert Lua's true to
1 and Lua's false to 0.  However, when it comes to retrieving the
value, it gets more complicated.  For example, a Vimscript plugin could
set a global flag:

  let g:my_flag = 1

When I call 'g.my_flag' from Lua, should it return a number or a
boolean?

Even if I don't worry about this, there's another issue.  Let's say I
assign a boolean to a variable in my current window:

  w.my_variable = true -- Vim sees this as let w:my_variable = 1

Now, when I read from that variable, what do I see?

  print(w.my_variable) -- does this output true, or 1?

My current ideas on how to handle these issues are as follows:

- Drop support for booleans entirely.  Scripts are free to use
  them for their own logic, but anything going/coming across the bridge
  is a number.  This means 'w.my_variable = true' will fail, and when
  calling Vim functions, we'll have to use a foreign-looking idiom such
  as if haslocaldir() ~= 0 then ... end.

- Assigning booleans to Vim variables will coerce them to Vim numbers,
  but no coercion will take place on the way back.  We'll need to use
  constructs like if w.my_variable ~= 0 then ... end or if
  toboolean(w.my_variable) then ... end.  However, Vim functions that
  are known to return boolean values can coerce their outputs to
  boolean, so we can still do if haslocaldir() then ... end.

- Remember which variables I assign booleans to, and treat them as
  such.  If I assign w.my_variable = true, the bridge will coerce the
  value of w:my_variable to a boolean when reading it, until a
  non-boolean value is assigned to that variable from Lua.

For those of you who are interested in taking an early look at this
project, its Git repository is located here:

https://github.com/hoelzro/queqiao

Any thoughts?

Thanks,
Rob

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