5 systematic ways of coming up with property-based tests

This is a cheat sheet based on a great talk "How to specify it! A guide to writing properties of pure functions" by John Hughes. This talk has a lot of information easy to forget so a cheat sheet may help you refreshing memories without watching the whole talk again.

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Published at 2021-02-10

Tags: functional programming, property-based tests, cheat sheet

Solution for Hackerrank problem: Basic Cryptanalysis

There's one programming puzzle I solved many years ago but I still remember it because of the unusual solution. Problem: You have a text encrypted with a simple monoalphabetic substitution cipher. You don't have the key but you have a dictionary. Every word in a text can be found in this dictionary. Find the original text. It can be solved by dynamically generating regular expressions.

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Published at 2021-01-29

Tags: algorithms, puzzle solution, cryptography, php

Solution for Project Euler Problem #700: Eulercoin

Problem: Imagine a sequence 1504170715041707*n mod 4503599627370517 where n is an integer increasing from 1. Find the subsequence of this sequence where every next element is smaller than a previous one.

All the solutions I've read about include brute force calculations. I found a better one and I can't stop myself from posting it.

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Published at 2021-01-15

Tags: algorithms, puzzle solution, recursion, scala

Generating CI/CD pipelines for microservices with Yeoman

TL;DR: You can create a Yeoman generator for your CI/CD pipelines. It's good, I tried.

Once you start multiplying services, you hit a problem of increased effort spent on non-business logic. With every new application you need to setup all the boilerplate: initial project, dependencies, running tests, building and deploying everything. Most of this things are very similar from project to project but they differ in details so you can copypaste a lot but you need to do it carefully so you don't break a lot of stuff by forgetting to update one line in a copypasted file. This needs a better solution.

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Published at 2020-12-17

Tags: yeoman, devops, ci cd

A good way how to validate types in TypeScript

TL;DR: I've created a typescript library fp-ts-type-check. You can use it to validate the structure of data you get from outside of your application.

Here's the situation: your typescript application needs to retrieve some object via some API. You make an API request and you get a successful response with some json. Probably it's the data you expect but you can't say for sure. Your actions?

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Published at 2020-11-18

Tags: typescript, functional programming, static typing, my library, api, json

A story about rubber ducks and functional programming

Once upon a time, I wanted to get a rubber duck. One rubber duck. I spent a lot of time looking for a perfect yellow rubber duck not representing any character and finally, I have found and bought it.

Later I accidentally found a much better rubber duck. I bought it also. That's one more rubber duck than I but I wasn't cruel enough to throw first one away. A big mistake.

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Published at 2020-07-31

Tags: story

Sudoku Solver in Scala Part 3: Generating cross-dependent test data

This is the last part of my learnings during writing a sudoku solver. It's about several iterations of a property-based test refactoring in an attempt to find the best way to generate input data.

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Published at 2020-04-28

Tags: sudoku, scala, functional programming, property-based tests

Sudoku Solver in Scala Part 2: Functions compose, methods don't

I keep writing about my learnings during writing a sudoku solver. This time we touch solver's logic and I have something to share about making the big functions out of the small ones.

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Published at 2020-04-17

Tags: sudoku, scala, functional programming

Sudoku Solver in Scala Part 1: Validated types

Sometimes you're trying to solve a puzzle so hard so you have to write a program to solve it. That happened to me with one specific sudoku so I wrote a sudoku solver.

I did some learning during this and I want to share them here. This part is about injecting validation into the type system.

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Published at 2020-04-09

Tags: sudoku, scala, functional programming, static typing

PHP doesn't want you to do microservices

As a PHP developer, I should probably rejoice when someone's saying "we do microservices in PHP". I don't. I'm fine with PHP and I like microservices but the combination is just bad. PHP is a tool for solving a narrow range of tasks (i.e. making websites) and if you're trying to do something out of this range (i.e. making microservices) — you're gonna have a bad time.

In this post, I tried to collect all microservice-related PHP problems I saw over the years.

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Published at 2019-09-09

Tags: php, microservices

Functional FizzBuzz in Scala with streams and higher order functions

I'm currently learning functional programming with scala and as a practice I've implemented FizzBuzz. To be honest, I made three different implementations of FizzBuzz but only the third one is good.

Stream.from(1) # Create infinite lazy stream from 1
  .map { (_, "") } # convert it to (number, word) tuple
  .map { x => if (x._1 % 3 == 0) (x._1, x._2 + "Fizz") else x } # Add "Fizz" to each 3rd word
  .map { x => if (x._1 % 5 == 0) (x._1, x._2 + "Buzz") else x } # Add "Buzz" to each 5th word
  .map { x => if (x._2 != "") x._2 else x._1.toString } # Take word or number
  .take(30) # Limit stream length
  .foreach(println) # Run everything and print results

It's even much better than usual imperative implementation and here's why.

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Published at 2019-05-09

Tags: scala, functional, streams, fizzbuzz

React Styleguidist usage examples in typescript files

React Styleguidist uses external markdown files to store usage examples. We wanted to use typescript for examples because reasons and we managed to do this with horrible solution. It includes custom webpack loader that parses typescript file with regular expressions and converts it to markdown. You could find parts of our code below.

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Published at 2019-03-27

Tags: react, react-styleguidist, typescript

Finding overlap among groups of date ranges

Imagine you have two groups of date ranges and you want to determine whether they overlap.

Nah, let's make it harder. Imagine you have two groups of include date ranges and two groups of exclude date ranges. Your task is to determine, whether there's a date that is present in both include groups and not present in exclude groups. How to do that?

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Published at 2018-01-23

Tags: algorithms, php

Running bash commands in parallel

Let's imagine you have a script like below and you want to make it faster.


echo "Started at `date +%Y-%m-%d\ %H:%M:%S`"

echo "Starting job 1"
sleep 5

echo "Starting job 2"
sleep 5

echo "Finished at `date +%Y-%m-%d\ %H:%M:%S`"

If it's ok to run jobs in parallel, you can easily do it with bash background jobs.

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Published at 2017-12-05

Tags: bash, tips

Difference between entities and value objects from philosophy perspective

Imagine a wooden ship. It's a quite famous ship - Theseus himself used it to return to Athens from Crete. After that Athenians tried to preserve it by replacing decayed planks with new ones. Many years passed and now we can say for sure that every part of the ship was replaced at least once. Is it still the same ship?

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Published at 2017-11-10

Tags: ddd, philosophy

3 ways to make your API slow

I had to fix performance issues of one API endpoint. A pretty Symfony endpoint that gathers some data from database, assembling it to some structure and returns it as json.

Performance started being an issue when major part of that "some data" started to be 60000 entities. In worst case response time was almost 20 seconds. "Ok", I thought, "60k is a big enough number to make it slow". But trace showed that retrieving data from DB isn't a slowest part. There were things taking almost 1/3 of request time each. And these things were easy to fix.

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Published at 2017-10-11

Tags: api, php, symfony, doctrine

How to make aliases for Symfony form fields

Imagine you want to rename form parameter but you also want it to accept old parameter name in requests to preserve backwards compatibility. Here's how you do it.

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Published at 2017-10-02

Tags: php, symfony, symfony forms

Harmful technical interview questions

Junior dev's life is hard an full of dangers. You come to technical interview and think "at least I'll learn something new from guys that know it better than me". Well, not really. Threre are some things that are ok in interviews and are totally wrong in real life. Here are some examples.

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Published at 2016-06-14

Tags: php, javascript, hr

Imagick resize filters comparison

So you want to shrink images with php and imagemagick. Here's samples of all filters so you can select the one you like most.

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Published at 2015-09-11

Tags: php, imagemagick, thumbs

Nicolas Cage as default avatar

No one asked me about this for months. And now it's done. Gravacage has it's own documented php library and site.

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Published at 2015-04-01

Tags: my library, ui

How to attach composer to Yii project

Sometimes I'm asked how to do this. It's boring to say that again and again so here's the instruction.

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Published at 2014-09-29

Tags: composer, php, yii

Why composer matters

I've heard about composer long before I started using it. I couldn't understand why it's so much cooler than downloading dependencies manually. I couldn't understand why it's worth running composer install after every code fetch.

This article is for guys like me in the past. If you're already using composer you can stop reading.

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Published at 2014-08-26

Tags: composer, php

Font Awesome icons for common buttons

Font Awesone is cool but it is sometomes hard to find the icon you really need because you forgot how it's called. And you have to look at every icon to find something you need.

Here's the names of icons for common buttons and operations.

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Published at 2014-07-07

Tags: font awesome, cheat sheet

Yii 1.1 does not support object cloning

You better watch out
You better not cry
You better not clone Yii objects
I'm telling you why
Object cloning is coming to town not supported in Yii 1.1.

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Published at 2014-06-26

Tags: yii, bugs

urmaul/url to make urls absolute and stuff

Copy-pasting two functions between projects is boring so I've created a GIANT COMPOSER PACKAGE with class with these two functions. It can convert relative urls to absolute and to add get parameters to urls. It's called urmaul/url.

Published at 2014-06-04

Tags: my library, php, urls