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There are several reasons for using the existing ''io'' and ''os'' namespaces.

The ''io.pipe'' function depends on the Lua core in order to return
newly-constructed file userdata. The ''io.lock'' and ''io.unlock'' functions
are both available as metamethods of file userdata (e.g. ''f:lock("r")''),
which seems a natural extension.

overloading file metatable, may as well overload io table too

Adding a function to change environment variables requires that the
implementation of the ''os.getenv'' function be changed, at least on the
Windows implementation. If it is not, then unexpected behavior occurs:

{{{require "ex"
assert( os.getenv"NEWVAR" == nil )
ex.setenv("NEWVAR", "value")
print( os.getenv"NEWVAR" ) -- prints "nil"
print( ex.getenv"NEWVAR" ) -- prints "value"
}}}

Another is that require "ex" changes the semantics of some standard functions,
notably os.remove.

The ''os.remove'' has similar requirements since on Windows, ''os.remove'' will
only remove non-directories unless ''require "ex"'' replaces its
implementation.

Even if none of the above implementation details mattered, it is the purpose of
this API to extend the Lua standard namespaces with additional functions.

It seems there are only two major concerns about using the existing namespaces.
First, there is concern that a future version of Lua might want to use one of
these names. This should not be a concern for one simple reason: this proposal
intends to be that future version. While it may not be the case that this
library would be distributed as part of the Lua core, it is the goal of this
proposal that this extension be recognized to be as much of a standard as
''package.loadlib'' which cannot be implemented in standard C.

The other major concern is that extending the existing namespaces would be
confusing to Lua users. The best solution to this issue is to make this API
(and its major implementations) a part of the standard Lua distribution.
Similarly to both ''io.popen'' and ''package.loadlib'', the functions proposed
here would be documented in the reference manual and clearly noted that they
are not supported on all platforms. Likewise, these functions would throw an
error when called on platforms which cannot provide an implementation.

goal: have standard methods when available
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