metatablesnow/issa

A runtime type validator with pretty errors and real types

Features

• Types from runtime checks
• Pretty yet precise errors
• Small, composable predicates

Installation

Issa is not published to Wally or Pesde currently. Simply copy the source code into a module.

Guide

Every function in Is returns a Predicate.

local Is = require(path.to.Issa)

IsAge = Is.Number()

You can call a predicate:

local age = IsAge(18) -- This will pass, and return the input (18)
IsAge("Oops!") -- This will error

Try a predicate:

local success, data = IsAge:Try("Oops!")
-- success is false, and data is the error message

local success, data = IsAge:Try(18)
-- success is true, and data is the input (18)

Type a predicate:

type Age = typeof(IsAge:Type())

local bobsAge: Age = "Oops!" -- This will warn you!

use them to build more complex predicates:

-- Predicates are chainable!
local IsAgeOrName = IsAge:Or(Is.String())

local IsAnimal = Is.Interface({
    Name = Is.Number()
    Age = IsAge
}) 

or even refine them:

local IsAdult = IsAge:Refine(function(fail, pass, age)
    if age < 18 then
        return fail("age is below 18")
    end

    return pass()
end)

IsAdult(13) -- This will error!