placing directories of temporary files under __tlacache__/

[johnyf]

As of v1.4.3, tlapm creates a separate directory for each TLA+ module it is invoked with. For example:

tlapm Dev.tla

will create the directory Dev.tlaps. In a directory with several TLA+ files, the list of files nearly doubles in length due to the generated directories. Instead of placing these directories under the same directory where the input TLA+ files are located, they could be placed under a __tlaps__ directory, leading to a directory tree of the form:

/workdir/Dev.tla
/workdir/Foo.tla
/workdir/Bar.tla
/workdir/__tlaps__/Dev.tlaps/
/workdir/__tlaps__/Foo.tlaps/
/workdir/__tlaps__/Bar.tlaps/

thus removing the clutter from the user's working directory. Another suggestion for naming this directory is __tlapscache__, or perhaps __tlacache__, which could be used also by TLC and other TLA-related tools.

The suggestion for using such a directory is inspired by Python's __pycache__ directories (described in PEP 3147), which in Python 3 avoid the clutter of *.pyc files that was created in the user's directory with Python 2.

Adding the pattern *.tlaps to a repository's .gitignore makes the TLAPS directories hidden in a VCS-aware editor (e.g., atom). However, one still needs to scroll past all the *.tlaps directories in the editor's file tree view pane. With the proposed change, this issue will be avoided.