lua-async-await.txt

*lua-async-await.txt*      For Neovim >= 0.9.4      Last change: 2024 March 31

==============================================================================
Table of Contents                          *lua-async-await-table-of-contents*

1. lua-async                                       |lua-async-await-lua-async|
  - What                                                |lua-async-await-what|
  - Why                                                  |lua-async-await-why|
  - How to use                                    |lua-async-await-how-to-use|

==============================================================================
1. lua-async                                       *lua-async-await-lua-async*

Synchronous like asynchronous for Lua.


WHAT                                                    *lua-async-await-what*

Take a look at before and after

**Before:**

>lua
    request('workspace/executeCommand', cmd_info, function(err, res)
      if err then
        log.error(err)
      else
        log.debug(res)
      end
    end, buffer)
<

**After:**

>lua
    -- on error, statement will fail throwing an error just like any synchronous API
    local result  = request('workspace/executeCommand', cmd_info, buffer)
    log.debug(result)
<


WHY                                                      *lua-async-await-why*

Well, callback creates callback hell.


HOW TO USE                                        *lua-async-await-how-to-use*

>lua
    local runner = require("async.runner")
    local wrap = require("async.wrap")
    local wait = require("async.waits.wait_with_error_handler")
    
    local function success_async(callback)
      local timer = vim.loop.new_timer()
    
      assert(timer)
    
      timer:start(2000, 0, function()
        -- First parameter is the error
        callback(nil, "hello world")
      end)
    end
    
    local function fail_async(callback)
      local timer = vim.loop.new_timer()
    
      assert(timer)
    
      timer:start(2000, 0, function()
        -- First parameter is the error
        callback("something went wrong", nil)
      end)
    end
    
    local function log(message)
      vim.print(os.date("%H:%M:%S") .. " " .. message)
    end
    
    vim.cmd.messages("clear")
    
    local nested = runner(function()
      local success_sync = wrap(success_async)
      local fail_sync = wrap(fail_async)
    
      local success_result = wait(success_sync())
      -- here we get the result because there is no error
      log("success_result is: " .. success_result)
    
      -- following is going to fail and error will get caught by
      -- the parent runner function's 'catch'
      wait(fail_sync())
    end)
    
    runner(function()
        log("starting the execution")
        -- just wait for nested runner to complete the execution
        wait(nested.run)
      end)
      .catch(function(err)
        log("parent error handler " .. err)
      end)
      .run()
<


OUTPUT ~

>txt
    18:44:46 starting the execution
    18:44:48 success_result is: hello world
    18:44:50 parent error handler ...-async-await/lua/async/waits/wait_with_error_handler.lua:14: ...-async-await/lua/async/waits/wait_with_error_handler.lua:14: something went wrong
<

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