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Imperative, Procedural & Declarative code

kealanparr profile image Kealan Parr ・2 min read

I am reading Pragmatic Programmer at the moment, an excellent book by Andy Hunt and Dave Thomas.

But I have forgotten about 3 times now when they talk about imperative, procedural, declarative and multi paradigm code.

So welcome back future Kealan, here we go again for the fourth time.

Software languages follow 2 broad paradigms.

Declarative paradigm

Languages following the declarative paradigm, have the code written specifying what you want to do, without saying how.

A super simple example of this is either:

SQL

SELECT * FROM customers
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or HTML

<div></div>
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In the above code examples, you aren't implementing the SELECT or how to render a div. You are just telling the computers what to do, without the how.

From this paradigm, there are sub-paradigms such as:

  • Functional programming.

Imperative or Procedural paradigm

Languages following the imperative/procedural paradigm, have the code written in a format of how to do something.

For example, if you do something like below:

for (let i = 0; i < arr.length; i++) {
     increment += arr[i];
}
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You are telling the computer exactly what to do. Iterate through the array called arr and add to increment each of the items in the array.

The vast majority of modern languages are imperative/procedural (or can be used in an imperative/procedural way).

Conclusion

A good example of a declarative command, would ask the computer to make you a cup of tea (I don't care how you do it, just bring me some tea).

Whilst imperatively, you would have to say

  • Go to the kitchen.
  • If there is a kettle in the room, and it has enough water for a cup of tea, turn on the kettle.
  • If there is a kettle in the room, and it doesn't have enough water for a cup of tea, fill the kettle with enough water for a cup of tea, then turn on the kettle.
  • etc. etc.

Can you see how I am implementing or telling the computer exactly what to do?

If you want to dig further into sub-paradigms in either of the paradigms, Wikipedia had a great (although pretty complex) graph found here: https://commons.wikimedia.org/wiki/File:Programming_paradigms.svg

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