Re: Readline read_history and write_history addition

On Monday 21 January 2008 01:27:35 pm Judah Jacobson wrote:

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On Jan 19, 2008 11:09 AM, Judah Jacobson wrote:

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On Jan 18, 2008 11:10 PM, Alexander Dunlap wrote:

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Hello all,

I'd like to propose the addition of read_history and write_history bindings to the readline library. I believe I've followed the instructions on the Haskell wiki appropriately and I've set up a ticket (with a patch) at http://hackage.haskell.org/trac/ghc/ticket/2053.

Essentially, the patch adds simple bindings so that Haskell programs can use Readline's read_history and write_history functions. This will be useful for the implementation of http://hackage.haskell.org/trac/ghc/ticket/2050 (add persistent history to GHCi) and potentially other applications.

Thanks for your time and consideration.

Alex

That patch looks good to me. While we're at it, can we also add the following related functions, which are used to control the maximum size of the history file? (They're also provided by editline.)

void clear_history(void); void stifle_history(int); int unstifle_history(void); int history_is_stifled(void);

One more suggestion, from Robert Dockins (author of the Shellac and

Shellac-readline packages):

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The only concern I have is that this patch doesn't seem to be handling errors properly. read_history and write_history should return errno, but this binding has them returning (). These functions do file operations and therefore can fail; we want (be able) to know when that happens.

I think we should just throw an error if those functions return a nonzero value; for example, we already do that in the functions readInitFile and parseAndBind.

Ha, I was just now composing an email to this effect. In addition, it would be nice for me if you could include: history_max_entries :: IO Int You can get this from readline by peeking this variable: foreign import ccall "readline/history.h &history_max_entries" history_max_entries :: Ptr CInt Then I could completely remove direct FFI bindings from my packages.

Thanks, -Judah