Try

(DEPRECATED) An asynchronous pcall-wrapper library for controlling the flow of error-prone, interdependent functions.

How to use

Upon requiring the Library, it returns a function called Try:

-- Without RoStrap
local Try = require(TryLibrary)

-- With RoStrap
local Resources = require(ReplicatedStorage:WaitForChild("Resources"))

local Try = Resources:LoadLibrary("Try")

API

Attempt Try(Function, ...)

Try calls pcall(Function, ...) on a separate thread, and returns a table Object called an Attempt.

Attempt

Attempt :Then(Callback)

This method takes a callback of the form <function, callable table> Callback(...), and pcalls it if the previous pcall didn't error, with ... being that which was returned by that pcall. This also returns the attempt, for further chaining.

local HttpService = game:GetService('HttpService')

Try(wait, 0.1)

    -- Try hashing the time
    :Then(function (Delta, ElapsedTime)
        return HttpService:GetAsync('http://md5.jsontest.com/?text=' .. Delta)
    end)

    -- Try decoding the response
    :Then(function (RawResponse)
        return HttpService:JSONDecode(RawResponse)
    end)

    -- Print the decoded response data
    :Then(function (Response)
        print('Input:', Response.original, '\nMD5:', Response.md5)
    end)

Attempt :Catch([string Patterns...], Callback)

This method takes a callback of the form Variant Callback(string Error, string Stack, Attempt FailedAttempt), and pcalls it if the previous pcall had an error. Errors can be optionally filtered by providing a list of patterns which the error should match, otherwise all errors are caught by the function. Once an attempt's error is caught, it will not be caught by the next chained :Catch method, unless Callback itself has an error. The attempt is then returned for chaining.

If the first returned value from the attempt is an Attempt, it will be executed and the method will process its errors.

local HttpService = game:GetService('HttpService')

Try(HttpService.GetAsync, HttpService, 'http://httpstat.us/404')
    :Then(function (Data)
        print('Found', Data)
    end)

    -- Catch when the URL doesn't exist
    :Catch('HTTP 404', function (Error, Stack, Attempt)
        warn('Not found, error:', Error)
    end)

    -- Catch any other error
    :Catch(function (Error, Stack, Attempt)
        warn('Unknown error:', Error)
    end)

httpstat.us is a good way to test Http request errors.

Attempt :Retry()

This method can only be called within a Catch callback. It retries the last function called in the chain before the error (with the same old arguments). Attempt.RetryCount is incremented each time the attempt is retried, and is reset after a Retry pcall doesn't error.

You can use this method to retry a sequence of interdependent function calls that fail, and even limit the number of, or space out, retries. For example:

local HttpService = game:GetService('HttpService')

Try(HttpService.GetAsync, HttpService, 'http://httpstat.us/503')
    :Then(function (Data)
        print('Found', Data)
    end)

    -- Catch when the server is having issues and retry
    :Catch('HTTP 503', 'Timeout was reached', function (Error, Stack, Attempt)

        -- Limit the number of retries to 3
        if Attempt.RetryCount < 3 then

            -- Space out each retry
            local BackoffTime = Attempt.RetryCount * 3 + 3
            warn('Retrying in', BackoffTime, 'seconds...')
            wait(BackoffTime)

            -- Retry the attempt
            return Attempt:Retry()

        -- Give up if retry limit reached
        else
            warn('Failed')
        end

    end)

    -- Catch any other errors
    :Catch(function (Error, Stack, Attempt)
        warn('Unknown error:', Error)
    end)

Attempt :Wait()

This method yields until all of the pcalls before it have finished running.

Try(wait, 0.5)
    :Then(wait)
    :Wait()
print("Hello!") -- Runs after all of the threads finish

A :Wait() can go anywhere in the Chain:

local Attempt = Try(wait, 2)

print("Hey!") -- This runs immediately after Try is called on a separate thread

Attempt
    :Wait() -- Wait until this Attempt's thread finishes yielding
    :Then(function(...) -- This is still on a separate thread
        wait(1)
        print("This was returned by wait(2)", ...)
    end)
print("The Attempt has finished yielding!")