12- Composing Functions

Jul 01, 2026 03:29 · 4:19 · English · Whisper Turbo · 2 Выступающие

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Let me show you how we can compose small functions to build more complex and

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interesting functions.

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So let's say we have a string in this format,

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key, colon,

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value.

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Now I want to pass the string through two transformations.

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First we want to replace the colon with an equal sign.

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So key equals value.

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That is our first transformation.

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Now in the second transformation,

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we want to add braces around the string.

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So second

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going to add curly braces and get something

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like this.

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So we're going to declare two small functions and then we're going to compose

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them to build a larger,

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more complex function.

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So first we declare a function of

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string and string.

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We call it replace colon

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and set it to a lambda expression like this.

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str goes to str .replace.

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We want to replace the colon with

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an equal sign,

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like this.

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Now the second function,

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so function of string and string,

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let's call this add braces,

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and set it to a lambda like this.

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str goes to,

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first we add the left brace,

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then we add our string,

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and then we add the right brace.

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Pretty straightforward,

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right?

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Now,

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there are two ways to compose functions.

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Here's one way.

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We start the replace colon function,

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then we call and then,

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exactly like how we chained multiple consumer objects.

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Here we should pass another function,

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so we pass add braces,

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now this returns a new function,

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we can store it somewhere,

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or we can directly call the apply method,

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pass our string,

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key colon value,

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and then get the result.

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As simple as that.

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So let's print it,

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and

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There you go.

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That's what we get.

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Beautiful.

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Now,

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once again, this is an example of declarative programming.

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So instead of writing instructions to specify how we should do

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something, we express what needs to be done.

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The details are somewhere else.

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So we have a bunch of small reusable functions and we're composing

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them to build something more complex.

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Now,

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when writing code like this,

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it's better to reformat our code like this.

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So we put

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each statement on a new line.

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That reads better.

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So replace colon,

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and then add braces,

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finally apply.

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Now we also have another method called compose.

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Compose is similar to and then,

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but it changes these functions in the reverse order.

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So if you want to achieve the same result using the compose method,

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we should write code like this.

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We start with the second function,

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add braces,

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we compose this with the first function,

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replace colon and then we apply key value

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to get the result and then print it.

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Take a look.

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We get the same result as before.

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So there are two ways to compose functions.

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Now if you're curious how these work,

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put the carrot over here on the top from the navigate menu go

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to declaration or use the shortcut.

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So here's the implementation

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of the and then method.

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So this method takes a function

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and it returns another function.

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Now,

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in the body of this function,

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first we make sure that the argument is not null,

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and here we return another function that is represented using a

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lambda expression,

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so we have this parameter of type t,

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first we call the apply method on this argument,

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we get the result,

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and then pass it to the apply method of the second function.

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Now the compose method is very similar,

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but it composes these functions in the reverse order.

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