This is a port of the RetroForth/ilo block editor to
RetroForth/nga. Much of this will be the same as the original
implementation, but there are some differences.

Retro/nga provides three words for interfacing with a block
store:

  block:set-file (s-)
  block:read     (na-)
  block:write    (na-)

This begins by using these to implement the `block:load` and
`block:save`. The initial block store is set to `ilo.blocks`.

~~~
'ilo.blocks block:set-file

:block:load block:read ;
:block:save block:write ;
~~~

In Retro/ilo, the memory is constrained to 65,536 cells, with a
defined memory map. Since Retro/nga does not do this, the block
buffer is allocated inline.

~~~
#0 , 'block:buffer d:create #1025 allot
~~~

Variables to track the current block and the number of blocks
are provided. Alter the `Blocks` count to match your actual
data store limits.

~~~
'Block var
#128 'Blocks var-n
~~~

`e:line` displays a line from the block buffer.

~~~
:e:line (n-)
  #64 n:mul block:buffer n:add
  #64 [ fetch-next c:put ] times drop nl ;
~~~


:e:for-each-line (q-)
  #16 [ block:buffer I #64 n:mul #64 s:middle swap &call sip ]
  indexed-times drop ;

~~~
{{
  :sep sp sp sp #6 [ '+----5---- s:put ] times '+--- s:put nl ;
  :l/n  I dup #10 lt? &sp if n:put sp ;
  :line l/n I e:line ;
  :lines #16 &line indexed-times ;
  :block# 'Editing_# s:put @Block n:put
          '_of_ s:put @Blocks n:dec n:put nl ;
---reveal---
  :list* nl #16 [ I e:line ] indexed-times ;
  :list# nl lines ;
  :list  nl sep lines sep block# ;
}}
~~~


~~~
&list 'e:Display var-n
{{
  :constrain @Block #0 #4095 n:limit !Block ;
---reveal---
  :set  &Block store constrain ;
  :save &Block fetch block:buffer block:save ;
  :load &Block fetch block:buffer block:load ;
  :next &Block v:inc constrain load ;
  :prev &Block v:dec constrain load ;
  :new  block:buffer #1024 [ #32 swap store-next ] times drop ;
  :edit set load @e:Display call ;
}}
~~~

~~~
:e:to-line #64 n:mul block:buffer n:add ;
:e:erase/line
  e:to-line #32 swap #64 [ dup-pair store n:inc ] times
  drop-pair ;
:e:replace &e:to-line dip [ over store n:inc ] s:for-each drop ;
:e:replace-at [ &e:to-line dip n:add ] dip
            [ over store n:inc ] s:for-each drop ;

:e:insert dup e:erase/line s:get e:replace ;
:e:insert-at s:get e:replace-at ;

:0 #0 e:insert ;
:1 #1 e:insert ;
:2 #2 e:insert ;
:3 #3 e:insert ;
:4 #4 e:insert ;
:5 #5 e:insert ;
:6 #6 e:insert ;
:7 #7 e:insert ;
:8 #8 e:insert ;
:9 #9 e:insert ;
:10 #10 e:insert ;
:11 #11 e:insert ;
:12 #12 e:insert ;
:13 #13 e:insert ;
:14 #14 e:insert ;
:15 #15 e:insert ;
~~~

~~~
:run &block:buffer s:evaluate ;

:use (block) set load run ;

:using (first,last)
  over n:sub swap set load run [ next run ] times ;
~~~


`titles` iterates through the blocks, displaying the title
(first line) of any block that does not start with a blank
space.

~~~
{{
  :setup  #64 block:buffer n:dec store ;
  :has-description? block:buffer fetch #32 -eq? ;
  :display  [ I n:put tab #0 e:line ] if ;
  :describe I set load has-description? display ;
  :save &Block fetch ;
  :restore &Block store load ;
---reveal---
  :titles save setup @Blocks &describe indexed-times restore ;
}}
~~~

{{
  'Hash var
  :reset  #64 block:buffer n:dec store ;
  :actual block:buffer n:dec dup #32 s:index/c s:left ;
  :code?  block:buffer fetch $( eq? ;
---reveal---
  :needs (s-)
    @Hash [ @Block swap
      s:hash !Hash
      @Blocks [ I set load reset code?
                     [ actual s:hash @Hash eq?
                       &run if ] if ] indexed-times
      !Block load ] dip !Hash ;
}}