150 lines
3.8 KiB
Text
150 lines
3.8 KiB
Text
# A New Listener
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The basic listener is very minimalistic. There are a few reasons
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for this.
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- I don't use it often (I generally code in files or blocks,
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using the listener only for brief tests)
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- A complex listener adds surface for bugs and incompatibilites
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due to terminal and host configurations
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- It's harder to pipe data in and out of a more complex listener
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This can be worked around in a number of ways. Tools like
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`rlwrap` can be used to provide a line editor and history, and
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one can always write their own custom listener...
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But sometimes it's nice to experiment a bit. This is a modestly
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expanded version of the listener, adding some new functionality
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and providing a more flexible base to build on.
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# Current Features
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- character breaking input
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- suggestions on hitting TAB
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- show stack on hitting ESC
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- use `retro-describe` to get help on CTRL+K
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# Loading
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retro -i -f alternate-listener.forth
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new-listener
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# The Code
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The RETRO image has a 512 cell buffer between the kernel and the
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high level code. This is used for the Text Input Buffer, or TIB.
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+------------------+
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| kernel | 0-1023
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| input buffer | 1024-1536
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| standard library | 1537+
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| ... |
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| system buffers | EOM - ???
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+------------------+
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~~~
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#1024 'TIB const
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~~~
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The listener needs to determine what to treat as the end of the
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token. I define `end-of-token?` for this.
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~~~
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:end-of-token? (c-f) hook
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{ ASCII:CR ASCII:LF ASCII:SPACE } a:contains? ;
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~~~
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It's possible to get an empty string as an input. This isn't
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any good, so I define `s:blank?` for this.
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~~~
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:s:blank? (s-sf) dup s:length n:zero? ;
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~~~
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There are certain keys I want to handle differently from others.
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The initial ones are backspace, tab, escape, and CTRL+K. I am
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defining handlers for these.
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First is backspace. I trap ASCII:BS and ASCII:DEL for this.
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~~~
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:handle:backspace (c-c) hook
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dup { ASCII:BS ASCII:DEL } a:contains?
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[ buffer:get buffer:get drop-pair ] if ;
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~~~
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Tab is used to display suggestions, based on the token input so
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far.
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~~~
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{{
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:prefix?
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TIB fetch 'prefix:_ [ #7 + store ] sip d:lookup n:-zero? ;
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:hint
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nl TIB prefix? [ n:inc ] if d:words-beginning-with nl
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TIB s:put ;
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---reveal---
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:handle:tab (c-c) hook
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dup ASCII:HT eq? [ buffer:get drop hint ] if ;
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}}
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~~~
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Control + k (`ASCII:VT`) will display help for the word being typed.
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This assumes that `retro-describe` is in your $PATH and that the
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typed text is a complete word name (without a prefix).
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~~~
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:handle:CTRL+K (c-c) hook
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dup ASCII:VT eq? [ buffer:get drop
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TIB 'retro-describe_"%s" s:format nl
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unix:system TIB s:put ] if ;
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~~~
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The escape key will be used to display the stack.
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~~~
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:handle:escape (c-c) hook
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dup ASCII:ESC eq?
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[ buffer:get drop nl &dump-stack dip nl TIB s:put ] if ;
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~~~
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To control the checks, I define two words. The first returns an
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array of handlers, the second processes them.
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~~~
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:special-keys (-a) hook
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{ &handle:backspace &handle:tab &handle:escape &handle:CTRL+K } ;
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:check (q-) hook
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&call a:for-each ;
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~~~
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And with these, I can quickly implement the `new-listener`.
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~~~
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{{
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:guard (-) buffer:end TIB lt? [ TIB buffer:set ] if ;
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:c:get (-c) as{ 'liii.... i #1 d }as dup buffer:add ;
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:s:get (-s) [ TIB buffer:set
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[ guard c:get special-keys check end-of-token? ] until
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buffer:start s:chop ] buffer:preserve ;
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:forever (q-) repeat &call sip again ;
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---reveal---
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:new-listener (-) hook
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'stty_cbreak unix:system
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[ s:get s:blank? &drop &interpret choose ] forever ;
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[ 'stty_cbreak unix:system
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#0 unix:exit ] &bye set-hook
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}}
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~~~
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All of the exposed words are hooks: your code can patch in and
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replace them as you see fit, making this much more mallable at
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runtime.
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Future things to (maybe) explore:
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- tab completion
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- line editing
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- input history
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