Add example teal files to parse

examples/tl-example.tl

@@ -0,0 +1,101 @@
+-- Sapmle file from: https://github.com/teal-language/tl/blob/master/docs/examples/files/src/main.tl
+
+-- files/src/main.tl
+-- Reads content from STDIN or file;
+-- writes content in uppercase to STDOUT or file.
+-------------------------------------------------------------------------------
+
+-- record to hold file handles
+local record Handles
+   input: FILE
+   output: FILE
+end
+
+-- a simple command-line parser
+local function parse_arguments(args: {string}): string, string
+   local i_name, o_name: string, string
+   local err: string
+   local i = 1
+   while i <= #args do
+      local a, b = args[i], args[i+1]
+      if a == "-i" then
+         if not b then
+            err = "-i name?"
+         else
+            i_name = b
+            i = i + 2
+         end
+      elseif a == "-o" then
+         if not b then
+            err = "-o name?"
+         else
+            o_name = b
+            i = i + 2
+         end
+      else
+         err = "unknown arg: " .. a
+      end
+      if err then
+         -- exit, giving a hint on the way out
+         error(err)
+      end
+   end
+   return i_name, o_name
+end
+
+-- create or return file handles
+local function get_fd(name: string, mode: io.OpenMode, default: FILE): FILE, string
+   if not name then
+      return default
+   end
+
+   local fd, err = io.open(name, mode)
+   if not fd then
+      return nil, err
+   end
+
+   return fd
+end
+
+-- get handles record
+local function get_handles(input_name: string, output_name: string): Handles
+   local handles: Handles = {}
+   local err: string
+
+   handles.input, err = get_fd(input_name, "r", io.stdin)
+   if err then
+      error(err)
+   end
+
+   handles.output, err = get_fd(output_name, "w", io.stdout)
+   if err then
+      error(err)
+   end
+
+   return handles
+end
+
+-- do some work using the file handles
+local function process_handles(h: Handles)
+   local lines = h.input:read("*a")
+   h.input:close()
+
+   -- simple example of doing work on the input:
+   -- convert it to ASCII uppercase
+   lines = lines:upper()
+
+   h.output:write(lines)
+   h.output:close()
+end
+
+local function main(args: {string}): integer
+   local input_name, output_name = parse_arguments(args)
+
+   local h = get_handles(input_name, output_name)
+
+   process_handles(h)
+
+   os.exit(0)
+end
+
+main(arg)