Is there a way to call require
in a Lua file, and have the module set the environment of the file that calls it? For example, if I have a DSL (domain specific language) that defines the functions Root
and Sequence
defined in a table, can I have something like setfenv(1, dslEnv)
in the module that allows me to access those functions like global variables?
The goal I in mind is using this is a behavior tree DSL in a way that makes my definition file look like this (or as close it as possible):
require "behaviortrees"
return Root {
Sequence {
Leaf "leafname",
Leaf "leafname"
}
}
without having to specifically bring Root
, Sequence
, and Leaf
into scope explicitly or having to qualify names like behaviortrees.Sequence
.
In short, I'm trying to make the definition file as clean as possible, without any extraneous lines cluttering the tree definition.
setfenv(1, dslEnv)
in the module that allows me to access those functions like global variables?Sure you can. You just have to figure out the correct stack level to use instead of the 1
in your setfenv
call. Usually you'd walk up the stack using a loop with debug.getinfo
calls until you find the require
function on the stack, and then you move some more until you find the next main chunk (just in case someone calls require
in a function). This is the stack level you'd have to use with setfenv
. But may I suggest a ...
require
in Lua is pluggable. You can add a function (called a searcher) to the package.loaders
array, and require
will call it when it tries to load a module. Let's suppose all your DSL files have a .bt
suffix instead of the usual .lua
. You'd then use a reimplementation of the normal Lua searcher with the differences that you'd look for .bt
files instead of .lua
files, and that you'd call setfenv
on the function return
ed by loadfile
. Something like this:
local function Root( x ) return x end
local function Sequence( x ) return x end
local function Leaf( x ) return x end
local delim = package.config:match( "^(.-)\n" ):gsub( "%%", "%%%%" )
local function searchpath( name, path )
local pname = name:gsub( "%.", delim ):gsub( "%%", "%%%%" )
local msg = {}
for subpath in path:gmatch( "[^;]+" ) do
local fpath = subpath:gsub( "%?", pname ):gsub("%.lua$", ".bt") -- replace suffix
local f = io.open( fpath, "r" )
if f then
f:close()
return fpath
end
msg[ #msg+1 ] = "\n\tno file '"..fpath.."'"
end
return nil, table.concat( msg )
end
local function bt_searcher( modname )
assert( type( modname ) == "string" )
local filename, msg = searchpath( modname, package.path )
if not filename then
return msg
end
local env = { -- create custom environment
Root = Root,
Sequence = Sequence,
Leaf = Leaf,
}
local mod, msg = loadfile( filename )
if not mod then
error( "error loading module '"..modname.."' from file '"..filename..
"':\n\t"..msg, 0 )
end
setfenv( mod, env ) -- set custom environment
return mod, filename
end
table.insert( package.loaders, bt_searcher )
If you put this in a module and require
it once from your main program, you can then require
your DSL files with the custom environment from .bt
files somewhere where you would put your .lua
files as well. And you don't even need the require("behaviortrees")
in your DSL files. E.g.:
File xxx.bt
:
return Root {
Sequence {
Leaf "leafname",
Leaf "leafname"
}
}
File main.lua
:
#!/usr/bin/lua5.1
require( "behaviortrees" ) -- loads the Lua module above and adds to package.loaders
print( require( "xxx" ) ) -- loads xxx.bt (but an xxx Lua module would still take precedence)