+ Eliminated vairous ad-hoc coersion functions between specific monads
(IO, Err, IOE, Check) in favor of more general lifting functions
(liftIO, liftErr).
+ Generalized many basic monadic operations from specific monads to
arbitrary monads in the appropriate class (MonadIO and/or ErrorMonad),
thereby completely eliminating the need for lifting functions in lots
of places.
This can be considered a small step forward towards a cleaner
compiler API and more malleable compiler code in general.
1. No temporary files are created.
2. The output of a system command is read lazily, making it feasible to
process large or even infinite output, e.g. the following works as
expected:
? "yes" | ? "head -5" | ps -lextext
The system_pipe (aka "?") command creates a temporary file _tmpi containing
the input of the system command. It *both* appends _tmpi as an extra argument
to the system command line *and* adds an input redirection "< _tmpi". (It
also uses and output redirection "> _tmpo" to captures the output of the
command.)
With this patch, the _tmpi argument is no longer appended to the command line.
This allows system_pipe to work with pure filters, such as the "tr" commands,
but it will no longer work with commands that require an input file name.
(It is possible to use write_file instead...)
TODO: it would also be fairly easy to eliminate the creation of the _tmpi and
_tmpo files altogether.
Add proper type checking of course-of-values tables:
+ Make sure that all subterms have the same type.
+ Resolve overloaded operators.
Note though that the GF book states in C.4.12 that the "course-of-values
table [...] format is not recommended for GF source code, since the
ordering of parameter values is not specified and therefore a
compiler-internal decision."
The CF parser in GF.Grammar.CF assigns function names to the rules, but they
are not always unique, causing rules to be dropped in the follwing CF->GF
conversion. So a pass has been added before the CF->GF conversion, to make
sure that function names are unique.
A comment says "rules have an amazingly easy parser", but the parser looks
like quick hack. It is very sloppy and silently ignores many errors, e.g.
- Explicitly given function names should end with '.', but if the do not, the
last character in the function name is silently dropped.
- Everything following a ';' is silently dropped.
Trailing spaces caused the command line parse to be ambiguous, and
ambiguous parses were rejected by function readCommandLine, causing
the cryptic error message "command not parsed".
