# Scale complexity in software applications

Sandro Maglione

Get in touch with meWeb development

28 February 2024

•6 min read

Sandro Maglione

Web development

Learn about a new paradigm to implement software applications at scale, using the type system to drive development:

- Return errors as values and collect them on the return type
- Define and compose services in layers using dependency injection
- Use the compiler to fix errors before releasing the app

This new way of building software is what Effect is all about 👇

## Software is complex

At the beginning it was all javascript, and it was a nightmare:

No types, anything can happen, no checks, no help. **No way to manage complexity at all**.

Some smart folks created types:

Great, but not so helpful. We barely know the parameters and what the function returns, but nothing else. Not much help in dealing with real-software complexity.

**Most programmers are stuck here**. No good 🤷🏼♂️

## Functional programming to the rescue (really?)

Some other smart folks (mathematicians) invented functional programming.

New ideas and types to scale complexity: Either, Option, **Functor, Applicative, Monad**...

Wait? What is this? We are no mathematicians, what is a Monad? Or better, who cares?

Unfortunately, the tools and terminology behind "pure" functional programming is scaring programmers away (and they do have a point).

## Complexity at scale

The solution is to **make the complexity explicit**, understandable, and readable, without jargon, all using types:

The return type defines **everything** that can happen:

`PaymentReceipt`

: If the function succeeds we get back all the information about the payment`ConnectionError | PaymentError | WrongParametersError`

: If the function fails, we know exactly why and where, so we can respond accordingly`PaymentService | AuthService`

: A complex system is composed by many moving parts, the type reports all the services required to make a payment

### How is this helpful

Types become our real co-pilot:

- Enforce providing all required services
- Enforce handling all errors
- Enforce creating valid response types

All possible issues are **managed and propagated by the type system**:

### There is more.

Every week I build a new open source project, with a new language or library, and teach you how I did it, what I learned, and **how you can do the same**. Join me and other 600+ readers.

## A problem of try and catch

"I don't get this, how does this help to scale complexity?"

Back to the origins, what can go wrong in the code below? 👇

After you read the implementation you spot a `throw`

for an invalid card. Is this enough?

Not really. What about `getCreditCard`

and `getIsCardValid`

?

Well, we don't know. The response type doesn't help.

We are

requiredto read (and understand 🤯) the internal implementation of both

This is a recursive problem: **for every function call** we must spot every `throw`

to handle all errors properly.

Solution: wrap everything in try/catch and call it a day 💁🏼♂️

Or even better 👎

We can call this

global reasoning: you must read and understand all functions implementations to manage complexity

### Local reasoning

Guess what? There is a solution for this:

The errors from `getIsCardValid`

and `getCreditCard`

are propagated and collected inside `makePayment`

.

Even better: we do not need to know the actual implementation:

the type signature is enough💡

This scales complexity: we can focus on each implementation knowing that all errors and dependencies are collected and checked by the type system.

We call this

local reasoning: you focus on the implementation of single function, and then compose them together.No need to read any other function implementation,

the type is enough

This is what Effect is all about.

Effect is the missing standard library for TypeScript: it provides a solid foundation of data structures, utilities, and abstractions to

make building applications easier at scale

If you are interested to learn more, every week I publish a new open source project and share notes and lessons learned in my newsletter. You can **subscribe here below** 👇

Thanks for reading.