petdance/scratch — Issue #509: 'parrot foo' automatically finds and invokes foo.pbc
Author: petdance
Created: 2011-11-01 05:35:00+00:00
State: open
Labels: Pri-normal, rfc, Sev-medium

I just recently committed examples/sdl/blue_rect.pl as an
example of exercising the SDL library using NQP. At the
beginning of the file the instructions read:

To run this file, execute the following command from
the Parrot directory:

$ ./parrot compilers/nqp/nqp.pbc examples/sdl/blue_rect.pl

Typing in that pathname is a bit of a pain -- what I'd really
like to be able to say is

$ ./parrot nqp examples/sdl/blue_rect.pl

and then since parrot can't immediately find anything called
'nqp' to execute, it looks for nqp.pbc in a standard location
or locations and invokes that. Similarly

$ ./parrot perl6 blue_rect.pl
$ ./parrot tgc --output=gen.pir PASTGrammar.tg
$ ./parrot abc
$ ./parrot tcl xyz.tcl
$ ./parrot pynie hello.py
etc.

Before we get too far, let me point out what I'm *not* asking for.
Specifically, I'm *not* asking for parrot to automatically select
an appropriate compiler based on a file's signature or magic, as
discussed in RT#32374. In other words, I'm *not* asking that

$ ./parrot examples/sdl/blue_rect.pl

be able to automatically determine an appropriate compiler
and invoke it on the script. While this is a very worthy and
important goal, at the moment there seem to be so many issues
around "how does Parrot register compilers and figure out which
one to use" that I fear it will be a while before this gets
implemented. I want something sooner than that.

I'm also explicitly *not* asking to try to handle or resolve
things based on Unix shebang lines, so that a file starting with

#!/path/to/parrot nqp

will automatically be executed with nqp. Again, it's something
we will eventually want to consider, but given the vagaries
of dealing with shebangs in so many different languages and
platforms it's not what I'm aiming to get from this ticket.

All I'm really looking is to be able to place the .pbc file for
a compiler or other application into a standard location where it
can be invoked from Parrot without having to give a complete
path to the .pbc file.

This could also have the benefit of simplifying Makefiles as well.
For example, when I moved nqp from languages/ to compilers/ , I had
to change the Makefile from

$(PARROT) $(PARROT)/languages/nqp/nqp.pbc ....

to

$(PARROT) $(PARROT)/compilers/nqp/nqp.pbc ...

While it was easy to do for this one case -- imagine if we had
10 or 20 applications that were using nqp as part of the
build process. With the approach proposed here, the Makefile
can have

$(PARROT) nqp ...

and it all just works.

I would also be willing to accept an option-based version of
this, such as (pick an appropriate option name or letter):

$ ./parrot --prog=nqp blue_rect.pl

Comments, suggestions, and (most importantly) implementations welcomed.
Thanks,

Pm
Trac ID #1196