Feature proposal: evaluate `Expression` on type-level

[0x009922]

Expression is a data-model structure that allows to build simple or complex expressions that are evaluated to something at runtime in Iroha.

TODO: show expression examples

Currently Expression implementation in TypeScript is completely dynamic and cannot guarantee that built Expression will not fail to evaluate at runtime. However, I think that evaluation mechanism is pretty determined, and Expression can be described as type-strong discriminated unions, thus, it is possible to develop a type that will compute the resulting type of an expression based on its shape.

I think this feature requires, first of all, improvement of @scale-codec/definition-compiler so it will generate enum factories that builds a concrete enum variant instead of telling TypeScript that build value is any of variants:

// now:

const val1 = OptionStr('Some', '4')
// type: OptionStr

// should be:

const val2 = OptionStr('Some', '4')
// type (roughly): { tag: 'Some', content: '4' } 

This change will allow to give TypeScript precise information about the built enums.

Secondly, iroha-javascript should provide:

export type EvaluateExpression<E extends Expression> = ... // evaluation prediction

Finally, there should be convenient builders that leverate this util type and will allow to build instructions with checked expressions, which should give a huve DX improvement.

Related issue in Java SDK:

• https://github.com/hyperledger/iroha-java/issues/159

[0x009922]

Related issue:

• https://github.com/hyperledger/iroha/issues/2826

[mversic]

we don't have expressions in the core anymore