Today we learn control flow, or branching
sometimes we need to execute a block of code only when it meets some condition
//Pseudocode
if conditionOne then doTaskOne
else if conditionTwo then doTaskTwo
else doSomethingElse
we introduce 2 ways of branching
if...then
let x = 10
if x > 0 then
printfn "Positive"
elif x = 0 then
printfn "Zero"
else
printfn "Negative"
x = 10, only the branch if x > 0 suits, the rest logic will not execute
match
// Match expression.
match test-expression with
| pattern1 [ when condition ] -> result-expression1
| pattern2 [ when condition ] -> result-expression2
| ...
equivalent example:
let x = 10
match x with
| x when x > 0 -> printfn "Positive"
| x when x = 0 -> printfn "Zero"
| _ -> printfn "Negative"
AND Pattern: we can combine conditions with (&&) operator, it hits when both condition match
let age = 10
match age with
| age when age > 0 && age < 14 -> printfn "Teenager"
| age when age > 14 -> printfn "Adults"
| _ -> printfn "Not born"
OR Pattern: we can combine patterns using the (||) operator to match multiple patterns
let x = 10
match x with
| x when x > 0 || x = 0 -> printfn "Positive or Zero"
| _ -> printfn "Negative"
we can even define a pattern matching function
type Shape =
| Square of side: double
| Rectangle of width: double * length: double
let getArea shape =
match shape with
| Square side -> side * side
| Rectangle (width, length) -> width * length
let square = Square 2.0
printfn $"The area of the square is {getArea square}"
let rect = Rectangle (2.0, 3.0)
printfn $"The area of the rect is {getArea rect}"
getArea function calculate the area according to different shape
The area of the square is 4
The area of the rect is 6
we didn't learn type yet, it defines a Union type here, and there is more powerful usage of match, we will introduce type, Union and discover more usage of match in the coming days
