[m-rev.] diff: io.get_environment_var on java

[Peter Wang]

On 2009-08-13, Paul Bone <pbone at csse.unimelb.edu.au> wrote:
> On Thu, Aug 13, 2009 at 11:27:42AM +1000, Peter Wang wrote:
> > On 2009-08-13, Paul Bone <pbone at csse.unimelb.edu.au> wrote:
> > > 
> > > When you use 'command()' to run a sub command and wait for it in Java does it
> > > support environment variables?  If so keeping a map of changed environment
> > > variables can be used to override any set for sub-processes as well as any
> > > retrieved by io.get_environment_var.
> > 
> > It's possible to do that but I'm not sure we should.
> 
> Without thinking about it too hard I can think of the following pros and cons.
> 
> Pros:
>     + It means one can export environment variables to child processes.
>     + set_environment_var has consistent behaviour across more backends.
> 
> Cons:
>     + It's more work, if we get what we want with less work then that's easier.
>     + If a programmer uses other foreign code to start child processes
>       environment variable bindings won't be exported.  This may not be what
>       programmers expect.
> 
> Why do you say we shouldn't do this?

Because of the second con.  io.set_environment_var will appear to work
until someone mixes Mercury and Java code, possibly resulting in a
subtle bug.

On the other hand we could add a version of io.call_system with takes a
list of environment variables, then people who need portability to Java
can use that instead.

Peter
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