Functional programming James Su - 2022/05/27 Sur f ing in the changing world 

Re-learn Actions, Calculations and Data 

Glossary • Actions - Functions with side e ff ects • A ff ected by when and how many times they are called. • Calculations - functions without any side e ff ects • Given the same input, returns the same output. • Data - facts about events • Immutable in functional programming languages • Can be immutable in object-oriented programming languages 

Analogy for information system 

Usage • Thinking a problem before coding • Coding a solution • Reading existing code 

Use case - Pending Emails 

Reading code • Look for Actions because they need the most attention. • Find code smell without running code. 

Reading code 

Thinking a problem before coding • What data we will need to capture (Data) • What decisions we will need to make (Calculations) • Clarifying problems needs attention (Actions) 

Thinking a problem 

Coding a solution • Changeability: Actions > Calculations > Data. • Few Actions, more Calculations and Data. 

Coding a solution 

Solution 

Re-learn Strati f ied design 

Strati f ied design A technique for building software in layers. 

What is software design? "using one’s aesthetic sense to guide programming choices to improve the ease of coding, testing, and maintaining software" 

How strati f ied design help us to develop aesthetic senses • Straightforward implementation • Abstraction barrier • Minimal interface • Comfortable layers 

Straightforward implementation 

Call graph • Arrows represent function calls • Functions are in di ff erent layers Visualizing our function calls 

Straightforward call functions from similar layers of abstraction 

Straightforward all functions in a layer should serve the same purpose 

Problems may exist in three levels • Interaction between layers • Implementation of one layer • Implementation of one function 

Use call graph • Global zoom level • Layer zoom level • Function zoom level to f ind problems in di ff erent levels 

Call graph practice Pending Emails 

Q & A