stop using tasks in start_reading/start_writing

We just need queues/streams for file I/O. No need to complect
concurrency concerns with them.

doc/manual.html

@@ -3600,35 +3600,26 @@ idiomatic Teliva uses some slightly different primitives.
 <hr><h3><a name="pdf-start_reading"><code>start_reading (fs, filename)</code></a></h3>
 
 <p>
-This function opens a file exclusively for reading, and returns a
-<code>channel</code> (NOT a file as in Lua) or <b>nil</b> on error.
-<a href='#pdf-channel:recv'><code>recv</code></a> from the channel to read a
-line at a time from the file.
+This function opens a file exclusively for reading, and returns an object (NOT
+a file handle as in Lua) or <b>nil</b> on error. If the returned object is
+stored in variable <code>f</code>, <code>f.read(format)</code> will read from
+the file. Legal values for <code>format</code> are identical to
+<a href='#pdf-file:read'><code>file:read(format)</code></a>.
 
 <p>
 (The <code>fs</code> parameter is currently unused. It will be used to pass in
 fake file systems for tests.)
 
-<p>
-<hr><h3><a name="pdf-character_by_character"><code>character_by_character(chanin, chanout)</code></a></h3>
-
-<p>
-This function converts a channel that can <a href='#pdf-channel:recv'><code>recv</code></a>
-a line at a time from a file into a channel that can <a href='#pdf-channel:recv'><code>recv</code></a>
-a character at a time. Don't try to mix by-line reads with by-character reads.
-Once a channel is passed into <code>character_by_character</code>, calling
-code should stop trying to use it.
-
 
 <p>
 <hr><h3><a name="pdf-start_writing"><code>start_writing(fs, filename)</code></a></h3>
 
 <p>
-This function opens a file exclusively for writing, and returns a
-<code>channel</code> (NOT a file as in Lua) or <b>nil</b> on error.
-<a href='#pdf-channel:send'><code>send</code></a> to the channel to write to
-the file. <code>close</code> on the channel will persist the changes and make
-them externally visible. All writes are hidden until <code>close</code>.
+This function opens a file exclusively for writing, and returns an object (NOT
+a file handle as in Lua) or <b>nil</b> on error. If the result is stored in
+variable <code>f</code>, <code>f.write(x)</code> will write <code>x</code> to
+the file. <code>f.close()</code> will persist the changes and make them
+externally visible. All changes will be hidden until <code>f.close()</code>.
 
 <p>
 (The <code>fs</code> parameter is currently unused. It will be used to pass in
@@ -4408,17 +4399,19 @@ Returns a value representing the JSON string <code>str</code>.
 
 
 <p>
-<hr><h3><a name="pdf-jsonf.decode"><code>jsonf.decode (chan)</code></a></h3>
+<hr><h3><a name="pdf-jsonf.decode"><code>jsonf.decode (f)</code></a></h3>
 
 
 <p>
-Returns a value representing the JSON string read from channel
-<code>chan</code>.
+Reads a value encoded in JSON from a file and returns it.
+<code>f</code> is the type of file object returned by
+<a href='#pdf-start_reading'><code>start_reading</code></a> (i.e. supporting
+<code>f.read(format)</code>).
 
+For example, suppose file <code>foo</code> contains '[1,2,3,{"x":10}]'. Then:
 <pre>
-     local channel = task.Channel:new()
-     channel:send('[1,2,3,{"x":10}]')
-     jsonf.decode(channel)                -- Returns { 1, 2, 3, { x = 10 } }
+     local infile = start_reading(nil, 'foo')
+     jsonf.decode(infile)                 -- Returns { 1, 2, 3, { x = 10 } }
 </pre><p>
 
 

life.tlv

@@ -522,7 +522,7 @@
     >  if infile == nil then return end
     >  local line_index = lines  -- quarter of the way down in pixels
     >  while true do
-    >    local line = infile:recv()
+    >    local line = infile.read()
     >    if line == nil then break end
     >    if line:sub(1,1) ~= '!' then  -- comment; plaintext files can't have whitespace before comments
     >      local col_index = cols

src/file.lua

@@ -1,42 +1,43 @@
 -- primitive for reading files from a file system (or, later, network)
--- returns a channel or nil on error
--- read lines from the channel using :recv()
--- recv() on the channel will indicate end of file.
+-- returns an object or nil on error
+-- read lines from the object using .read() with args similar to file:read()
+-- read() will indicate end of file by returning nil.
 function start_reading(fs, filename)
-  local result = task.Channel:new()
   local infile = io.open(filename)
   if infile == nil then return nil end
-  task.spawn(reading_task, infile, result)
-  return result
-end
-
-function reading_task(infile, chanout)
-  for line in infile:lines() do
-    chanout:send(line)
+  return {
+    read = coroutine.wrap(function(format)
+      while true do
+        if format == nil then format = '*l' end
+        format = coroutine.yield(infile:read(format))
       end
-  chanout:send(nil)  -- eof
+    end),
+  }
 end
 
 -- primitive for writing files to a file system (or, later, network)
--- returns a channel or nil on error
--- write to the channel using :send()
--- indicate you're done writing by calling :close()
--- file will not be externally visible until :close()
+-- returns an object or nil on error
+-- write to the object using .write()
+-- indicate you're done writing by calling .close()
+-- file will not be externally visible until .close()
 function start_writing(fs, filename)
   if filename == nil then
     error('start_writing requires two arguments: a file-system (nil for real disk) and a filename')
   end
-  local result = task.Channel:new()
   local initial_filename = temporary_filename_in_same_volume(filename)
   local outfile = io.open(initial_filename, 'w')
   if outfile == nil then return nil end
-  result.close = function()
-    result:send(nil)  -- end of file
+  return {
+    write = coroutine.wrap(function(x)
+      while true do
+        x = coroutine.yield(outfile:write(x))
+      end
+    end),
+    close = function()
       outfile:close()
       os.rename(initial_filename, filename)
-  end
-  task.spawn(writing_task, outfile, result)
-  return result
+    end,
+  }
 end
 
 function temporary_filename_in_same_volume(filename)
@@ -57,31 +58,3 @@ function temporary_filename_in_same_volume(filename)
     i = i+1
   end
 end
-
-function writing_task(outfile, chanin)
-  while true do
-    local line = chanin:recv()
-    if line == nil then break end  -- end of file
-    outfile:write(line)
-  end
-end
-
--- start_reading reads line by line by default
--- this helper permits character-by-character reading
-function character_by_character(chanin, buffer_size)
-  local chanout = task.Channel:new(buffer_size or 50)
-  task.spawn(character_splitting_task, chanin, chanout)
-  return chanout
-end
-
-function character_splitting_task(chanin, chanout)
-  while true do
-    local line = chanin:recv()
-    if line == nil then break end
-    local linesz = line:len()
-    for i=1,linesz do
-      chanout:send(line:sub(i, i))
-    end
-  end
-  chanout:send(nil)  -- end of file
-end

src/jsonf.lua

@@ -67,7 +67,7 @@ local literal_map = {
 
 local function skip_spaces(infile)
   while true do
-    local c = infile:recv()
+    local c = infile.read(1)
     if c == nil then break end
     if space_chars[c] == nil then return c end
   end
@@ -79,7 +79,7 @@ local function next_chars(infile, set, firstc)
   local res = {firstc}
   local nextc
   while true do
-    nextc = infile:recv()
+    nextc = infile.read(1)
     if nextc == nil then break end
     if set[nextc] then break end
     table.insert(res, nextc)
@@ -121,27 +121,27 @@ local function parse_string(infile, firstc)
   local res = {}
 
   while true do
-    local chr = infile:recv()
+    local chr = infile.read(1)
     if chr == nil then break end
     local x = chr:byte()
 
     if x < 32 then
       error("control character in string")
     elseif chr == '\\' then
-      local c = infile:recv()
+      local c = infile.read(1)
       if c == nil then break end
       if c == "u" then
         local hex = ''
-        c = infile:recv()
+        c = infile.read(1)
         if c == nil then break end
         hex = hex..c
-        c = infile:recv()
+        c = infile.read(1)
         if c == nil then break end
         hex = hex..c
-        c = infile:recv()
+        c = infile.read(1)
         if c == nil then break end
         hex = hex..c
-        c = infile:recv()
+        c = infile.read(1)
         if c == nil then break end
         hex = hex..c
         if not hex:match('^%x%x%x%x') then
@@ -155,7 +155,7 @@ local function parse_string(infile, firstc)
         table.insert(res, escape_char_map_inv[c])
       end
     elseif chr == '"' then
-      return table.concat(res), infile:recv()
+      return table.concat(res), infile.read(1)
     else
       table.insert(res, chr)
     end
@@ -170,7 +170,7 @@ local function parse_number(infile, firstc)
   local res = {firstc}
   local nextc
   while true do
-    nextc = infile:recv()
+    nextc = infile.read(1)
     if nextc == nil then break end
     if delim_chars[nextc] then break end
     table.insert(res, nextc)
@@ -295,14 +295,6 @@ end
 
 
 function jsonf.decode(infile)
-  return decode2(character_by_character(infile))
-end
-
-
-function decode2(infile)
-  if not ischannel(infile) then
-    error("expected channel, got " .. type(f))
-  end
   local firstc = skip_spaces(infile)
   local res, nextc = parse(infile, firstc)
   if nextc then

zet.tlv

@@ -3732,8 +3732,8 @@
     >switch to new file API for writing
   write_zettels:
     >function write_zettels(outfile)
-    >  outfile:send(json.encode(zettels))
-    >  outfile:close()
+    >  outfile.write(json.encode(zettels))
+    >  outfile.close()
     >end
 - __teliva_timestamp:
     >Thu Mar 10 04:21:28 2022