new API for file operations

File operations now always return a channel (or nil on error or
permission denied).

When start_reading() from a filename, you can repeatedly :recv() from
the channel it returns.
When :recv() returns nil, you're at the end of the file. Stop.

When you start_writing() to a filename, you can repeatedly :send() to
the channel it returns.
When you're done writing, :close() the channel. Writes to the file won't
be externally visible until you do.

To make this work I'm now always starting up the scheduler, so I need to
fix sieve.tlv.

Transparently running the scheduler is an abstraction, and whenever I
create an abstraction I always worry about how it might fail. There's
a hopefully-clear error when you read past end of a file.

1 files changed, 11 insertions, 0 deletions

diff --git a/src/task.lua b/src/task.lua
index 8d03316..3b00ef6 100644
--- a/src/task.lua
+++ b/src/task.lua
@@ -380,6 +380,17 @@ _M.RECV      = RECV
 _M.SEND      = SEND
 _M.NOP       = NOP
 
+-- Specific to Teliva
+function spawn_main()
+  task.spawn(main)
+  task.scheduler()
+  assert(false, "Teliva's scheduler ran out of work; this shouldn't happen.\n"..
+                "Either a channel is blocked forever or you're reading past\n"..
+                "the end of a file (after recv() returned nil).\n")
+  curses.nodelay(true)
+  curses.getch()
+end
+
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 -- Tests