Basic Syntax

This article will cover some very basic syntax elements to jump start the learning of F#. It is not intended to provide a full explanation of each construct so as to make it short.

Assignment

let x = 10

let y = if x> 10 then 1 else 2

let mutable z = 1
z <- z + 1

Notes:
1. Value of x cannot be changed. So we refer x as a value instead of a variable.
2. z is mutable
3. Use <- operator to change the value of a mutable value

4. Specifying a type is not necessary as the type will be inferred by the RHS value.

Function Declaration

let f n = 10 * n + 2

let f a b = a * 2 + b

Notes:
1. No parenthesis is surrounding the argument
2. No comma to separate arguments

Calling a function

let x = f 10
let y = f 10 + 1

let z = f (x + 10)

Notes:
1. No parenthesis is surrounding the argument

2. y = x +1 as function calling has a higher precedence than binary operators

3. Parenthesis is used to change the association

Recursion

let rec f n = if n > 0 then (f n-1) * 2 else 1

Notes:
1. rec prefix must be used to allow a function to call itself.

2. Recursive function must have a terminal case (e.g. n = 0 -> 1).

Looping

for i = 1 to 10 do printfn i

for i = 1 to 10 do
printf "Hello,"
printfn "World"

Notes:
1. printf and printfn are built-in functions for printing to console. printfn terminates the line with a carriage return
2. Indentation is significant to define the boundary of the block (so no next statement is required)

Conditional

let f n = if n > 10 then

let m = 20

let p = m + n

n

else

n - 1

Notes:

1. Indentation is used to define the block

2. Last expression within a block will be used as the return value

3. If the else part is not defined, compilation error will be resulted

This concludes a general introduction to the basic syntax of F#.