Second Version

[macabeus]

After nice discussions, the second version of this proposals comes with the following changes:

• add parameter on handle block, to avoid shadowing problem and give more symmetry with catch block (https://github.com/macabeus/js-proposal-algebraic-effects/issues/16)
• doesn't allow to use resume outside of handle block AND must be in handle block directly (https://github.com/macabeus/js-proposal-algebraic-effects/issues/8) (https://github.com/macabeus/js-proposal-algebraic-effects/issues/9)
• throw error if there is an unhandled effect (https://github.com/macabeus/js-proposal-algebraic-effects/issues/8#issuecomment-570058274)
• perform always should return a value, even if no resume is called (https://github.com/macabeus/js-proposal-algebraic-effects/issues/8#issuecomment-570052778)

(each commit is one of the changes above)

TODOs

We still need to discuss more about:

• Should we implicitly inject the effects? No @@?
• How will the effect interact with the ecosystem of TypeScript?
• Alternative Syntax to avoid new keywords
• When we could use perform expression?