Hi,

Is there any way of trapping keystrokes in Haskell, modifying them, and then echoing?

Basically I want to give the user a prompt like:
>

and then have whatever they type appear in UPPERCASE regardless of whether caps lock was on or not.

By default Haskell seems to echo characters in whatever case they were typed. I want to sneak in a toUpper in before the Chars get echoed.

Thanks

Mark Spezzano


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Hi Mark,

Thanks, Neil

On Sun, Jan 31, 2010 at 8:47 AM, Mark Spezzano
< - > wrote:
> Hi,
>
> Is there any way of trapping keystrokes in Haskell, modifying them, and then echoing?
>
> Basically I want to give the user a prompt *like:
>>
>
> and then have whatever they type appear in UPPERCASE regardless of whether caps lock was on or not.
>
> By default Haskell seems to echo characters in whatever case they were typed. I want to sneak in a toUpper in before the Chars get echoed.
>
> Thanks
>
> Mark Spezzano
>
>
> _______________________________________________
> Haskell-Cafe mailing list
>

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>

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>
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import System.IO
import Data.Char

main = do
hSetEcho stdin False
hSetBuffering stdin NoBuffering
hSetBuffering stdout NoBuffering
scanLine
where scanLine = do
c <- hGetChar stdin
putChar . toUpper $ c
scanLine


Am Sonntag, den 31.01.2010, 19:17 +1030 schrieb Mark Spezzano:
> Hi,
>
> Is there any way of trapping keystrokes in Haskell, modifying them, and then echoing?
>
> Basically I want to give the user a prompt like:
> >
>
> and then have whatever they type appear in UPPERCASE regardless of whether caps lock was on or not.
>
> By default Haskell seems to echo characters in whatever case they were typed. I want to sneak in a toUpper in before the Chars get echoed.
>
> Thanks
>
> Mark Spezzano
>
>
> _______________________________________________
> Haskell-Cafe mailing list
>

Code:

Content visible to registered users only.

>

Code:

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Michael Hartl wrote:
> import System.IO
> import Data.Char
>
> main = do
> hSetEcho stdin False
> hSetBuffering stdin NoBuffering
> hSetBuffering stdout NoBuffering
> scanLine
> where scanLine = do
> c <- hGetChar stdin
> putChar . toUpper $ c
> scanLine
>

Last time I tried something like this [on Windows], it didn't seem to
work. I wanted to trap arrow keys and so forth, but they seem to be
being used for input history. (I.e., pressing the up-arrow produces
previously-entered lines of text, and none of this appears to be
reaching the Haskell program itself.) Has this changed since I tried it
last year?

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I've tried this example and it just lets me type in anything in CAPITALS, which is nice, but Delete key doesn't delete and the arrow keys unfortunately let me manoeuvre the cursor all over the screen. Also the biggest problem is that Enter doesn't terminate the input session.

Isn't there a simple way to do something like this?

Surely Haskell must have a standard getLine function that support CAPITALS and backspacing and no arrow keys. Arrows keys with history would be nice.

Mark


On 31/01/2010, at 11:27 PM, Andrew Coppin wrote:

> Michael Hartl wrote:
>> import System.IO
>> import Data.Char
>>
>> main = do
>> hSetEcho stdin False
>> hSetBuffering stdin NoBuffering
>> hSetBuffering stdout NoBuffering
>> scanLine
>> where scanLine = do c <- hGetChar stdin
>> putChar . toUpper $ c
>> scanLine
>>
>
> Last time I tried something like this [on Windows], it didn't seem to work. I wanted to trap arrow keys and so forth, but they seem to be being used for input history. (I.e., pressing the up-arrow produces previously-entered lines of text, and none of this appears to be reaching the Haskell program itself.) Has this changed since I tried it last year?
>
> _______________________________________________
> Haskell-Cafe mailing list
>

Code:

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>

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>
>

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It might be worth looking at something like a curses library.

On Mon, Feb 1, 2010 at 4:45 PM, Mark Spezzano
< - > wrote:
> I've tried this example and it just lets me type in anything in CAPITALS, which is nice, but Delete key doesn't delete and the arrow keys unfortunately let me manoeuvre the cursor all over the screen. Also the biggest problem is that Enter doesn't terminate the input session.
>
> Isn't there a simple way to do something like this?
>
> Surely Haskell must have a standard getLine function that support CAPITALS and backspacing and no arrow keys. Arrows keys with history would be nice.
>
> Mark
>
>
> On 31/01/2010, at 11:27 PM, Andrew Coppin wrote:
>
>> Michael Hartl wrote:
>>> import System.IO
>>> import Data.Char
>>>
>>> main = do
>>> Â*hSetEcho stdin False
>>> Â*hSetBuffering stdin NoBuffering
>>> Â*hSetBuffering stdout NoBuffering
>>> Â*scanLine
>>> Â* Â* Â*where scanLine = do Â* Â* Â* Â* Â* Â* Â* c <- hGetChar stdin
>>> Â* Â* Â* Â* Â* Â* Â*putChar . toUpper $ c
>>> Â* Â* Â* Â* Â* Â* Â*scanLine
>>>
>>
>> Last time I tried something like this [on Windows], it didn't seem to work. I wanted to trap arrow keys and so forth, but they seem to be being used for input history. (I.e., pressing the up-arrow produces previously-entered lines of text, and none of this appears to be reaching the Haskell program itself.) Has this changed since I tried it last year?
>>
>> _______________________________________________
>> Haskell-Cafe mailing list
>>

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>>

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>>
>>
>
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> Last time I tried something like this [on Windows], it didn't seem to
> work. I wanted to trap arrow keys and so forth, but they seem to be being
> used for input history. (I.e., pressing the up-arrow produces
> previously-entered lines of text, and none of this appears to be reaching
> the Haskell program itself.) Has this changed since I tried it last year?

Doesn't work in windows, at least up till 6.10.1. There's a work-around
though.

{-# LANGUAGE ForeignFunctionInterface #-}

import Data.Char
import Control.Monad (liftM, forever)
import Foreign.C.Types

getHiddenChar = liftM (chr.fromEnum) c_getch
foreign import ccall unsafe "conio.h getch"
c_getch :: IO CInt

main = do
forever $ do
c <- getHiddenChar
putStrLn $ show (fromEnum c)


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Tim Attwood wrote:
>> Last time I tried something like this [on Windows], it didn't seem to
>> work. I wanted to trap arrow keys and so forth, but they seem to be
>> being used for input history. (I.e., pressing the up-arrow produces
>> previously-entered lines of text, and none of this appears to be
>> reaching the Haskell program itself.) Has this changed since I tried
>> it last year?
>
> Doesn't work in windows, at least up till 6.10.1. There's a
> work-around though.
>
> {-# LANGUAGE ForeignFunctionInterface #-}
>
> import Data.Char
> import Control.Monad (liftM, forever)
> import Foreign.C.Types
>
> getHiddenChar = liftM (chr.fromEnum) c_getch
> foreign import ccall unsafe "conio.h getch"
> c_getch :: IO CInt
>
> main = do
> forever $ do
> c <- getHiddenChar
> putStrLn $ show (fromEnum c)

Thanks for the info.

Does anyone know how this is related to the "haskeline" package on Hackage?

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On Fri, Feb 5, 2010 at 10:41 AM, Andrew Coppin
< - > wrote:
> Tim Attwood wrote:
>>>
>>> Last time I tried something like this [on Windows], it didn't seem to
>>> work. I wanted to trap arrow keys and so forth, but they seem to be being
>>> used for input history. (I.e., pressing the up-arrow produces
>>> previously-entered lines of text, and none of this appears to be reaching
>>> the Haskell program itself.) Has this changed since I tried it last year?
>>
>> Doesn't work in windows, at least up till 6.10.1. There's a work-around
>> though.
>>
>> {-# LANGUAGE ForeignFunctionInterface #-}
>>
>> import Data.Char
>> import Control.Monad (liftM, forever)
>> import Foreign.C.Types
>>
>> getHiddenChar = liftM (chr.fromEnum) c_getch
>> foreign import ccall unsafe "conio.h getch"
>> *c_getch :: IO CInt
>>
>> main = do
>> *forever $ do
>> * * c <- getHiddenChar
>> * * putStrLn $ show (fromEnum c)
>
> Thanks for the info.
>
> Does anyone know how this is related to the "haskeline" package on Hackage?

The haskeline package provides a readline-like library for reading in
a line of input with arrow keys, tab completion, etc. It works on
both Windows and unix platforms. Documentation and a full list of
features can be found at .

On Windows, haskeline gets all user input by calling Win32 API
functions such as ReadConsoleInputW:

That function returns an INPUT_RECORD struct with information about
key press events (among others); those includes simple characters,
arrow keys, page up/down, etc. AFAIK that's the only way to get at
such events in the Windows console; there's no effective analogue to
the unix setting, where e.g. pressing the up key causes stdin to
receive the ANSI key sequence "\ESC[A".

The source code of haskeline has examples of how to import and use
those API functions:
Best,
-Judah
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