How to use for loop to iterate ranges and enumerable types in F# Code

For loops are used to execute the code repeatedly for a condition meet.

It is used to iterate an array or list types.

F# provides two types of for loops.

for loop iterate ranges: Simple for loop with for to/downto to iterate the values with given start and increment/decrement until max value.
for in loop to iterate range of values in Enumerable types such as array, set, collection types

F# For loops examples

for loop contains for to and downto versions

for to iterate with the initial value, increments until the end value is met. for downto iterates with an initial value, decrements until the end value is met. syntax


for variable=initial_expression to end_expression do 
//body

for variable=initial_expression downto end_expression do 
//body

Here is a for to loop example

for i = 1 to 3 do
 printfn "%d" i;

Output:

1
2
3

Here is a for downto loop example

for i = 3 downto 1 do
 printfn "%d" i;

Output:

3
2
1

For in-loop to iterate enumerable types

for in-loop to iterate types such as collections

Syntax

for pattern in enumerable_list
// body

Here is an example [1..3] is a range of values from 1 to 3.

for i in  [1..3] do
 printfn "%d" i;

Another example of iterating a List of numbers

 let numbers = [ 1;7;9;10 ];;

for value in  numbers do
 printfn "%i" value;

Output:

F# - For Loops

F# For loops examples