Saturday, June 6, 2009

F# Interactive on Mac OS X

Installing F# on Mac OS X is easy (with MacPorts):

$ sudo port install fsharp

I have version installed. Microsoft released a newer version several weeks ago, however it doesn't seem to have made it into MacPorts yet. Then to start F# Interactive:
$ fsi --readline --no-gui

There is basic history with the up/down arrows, but the usual emacs key bindings are not available, so entering and editing text is very slow and painful. I tried to fix this with rlwrap.
$ sudo port install rlwrap

As fsi is already using readline, rlwrap needs the -a option, See the man page for details, but on the mac you are required to provide a string (representing a password prompt the wrapped application might show) argument for this option. It is completely unnecessary for me at the moment, so I just picked something obvious as a placeholder.
$ rlwrap -aPassword: fsi --readline --no-gui

F# Interactive starts up with the usual splash text, but there seems to be some control characters automatically input and the console clears to something like this:
- 0;3R0;3R;3R;3R;3R;3R;3R

The emacs key bindings work, so this text can be deleted with C-a C-k and terminating the now empty line as per normal in fsi with ;; brings up the usual fsi prompt.

Unfortunately, if you type in an invalid expression eg. x = 3;;, the cursor is placed in the middle of the error message. When pressing up arrow to go back through the history, sometimes the prompt is replaced by partial text from a viewed history line.

So this is a pretty dodgy solution. If anyone knows how to get it to work properly, please leave a comment.

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