# File I/O

~~~
{{
  'io:Filesystem var
  :identify
    @io:Filesystem n:zero? [
      #4 io:scan-for dup n:negative?
      [ drop 'IO_DEVICE_TYPE_0004_NOT_FOUND s:put nl ]
      [ !io:Filesystem ] choose ] if ;
  ---reveal---
  :io:file-operation identify @io:Filesystem io:invoke ;
}}
~~~

This implements words for interfacing with the POSIX file I/O words if
you are using an interface supporting them. All of these are in the
`file:` namespace.

These are pretty much direct wrappers for fopen(), fclose(), etc.

First up, constants for the file modes.

| # | Used For           |
| - | ------------------ | 
| R | Mode for READING   |
| W | Mode for WRITING   |
| A | Mode for APPENDING |

~~~
#0 'file:R const
#1 'file:W const
#2 'file:A const
#3 'file:R+ const
~~~

For opening a file, provide the file name and mode. This will return a
number identifying the file handle.

~~~
:file:open  (sm-h) #0 io:file-operation ;
~~~

Given a file handle, close the file.

~~~
:file:close (h-) #1 io:file-operation ;
~~~

Given a file handle, read a character.

~~~
:file:read  (h-c) #2 io:file-operation ;
~~~

Write a character to an open file.

~~~
:file:write (ch-) #3 io:file-operation ;
~~~

Return the current pointer within a file.

~~~
:file:tell  (h-n) #4 io:file-operation ;
~~~

Move the file pointer to the specified location.

~~~
:file:seek  (nh-) #5 io:file-operation ;
~~~

Return the size of the opened file.

~~~
:file:size  (h-n) #6 io:file-operation ;
~~~

Given a file name, delete the file.

~~~
:file:delete (s-) #7 io:file-operation ;
~~~

Flush pending writes to disk.

~~~
:file:flush (f-) #8 io:file-operation ;
~~~

Given a file name, return `TRUE` if it exists or `FALSE` otherwise.

~~~
:file:exists?  (s-f)
  file:R file:open dup n:-zero?
  [ file:close TRUE ]
  [ drop FALSE ] choose ;
~~~

~~~
:file:open<for-reading> (s-nn)
  file:R file:open dup file:size swap ;

:file:open<for-append> (s-nn)
  file:A file:open dup file:size swap ;

:file:open<for-writing> (s-n)
  file:W file:open ;
~~~

With that out of the way, we can begin building higher level functionality.

The first of these reads a line from the file. This is read to `here`; move
it somewhere safe if you need to keep it around.

The second goes with it. The `for-each-line` word will invoke a combinator
once for each line in a file. This makes some things trivial. E.g., a simple
'cat' implementation could be as simple as:

  'filename [ s:put nl ] file:for-each-line

~~~
{{
  'FID var
  'Size var
  'Action var
  'Buffer var
  :-eof? (-f) @FID file:tell @Size lt? ;
  :preserve (q-) &FID [ &Size [ call ] v:preserve ] v:preserve ;
---reveal---
  :file:read-line (f-s)
    !FID
    [ here dup !Buffer buffer:set
      [ @FID file:read dup buffer:add
        [ ASCII:CR eq? ] [ ASCII:LF eq? ] [ ASCII:NUL eq? ] tri or or ] until
        buffer:get drop ] buffer:preserve
    @Buffer ;

  :file:for-each-line (sq-)
    [ !Action
      file:open<for-reading> !FID !Size
      [ @FID file:read-line @Action call -eof? ] while
      @FID file:close
    ] preserve ;
}}
~~~

`file:slurp` reads a file into a buffer.

~~~
{{
  'FID var
  'Size var
---reveal---
  :file:slurp (as-)
    [ file:open<for-reading> !FID !Size
      buffer:set
      @Size [ @FID file:read buffer:add ] times
      @FID file:close
    ] buffer:preserve ;
}}
~~~

~~~
{{
  'FID var
---reveal---
  :file:spew (ss-)
    file:open<for-writing> !FID
    [ @FID file:write ] s:for-each
    @FID file:close ; 
}}
~~~