Introduction To F# I/O

F# IO enables you to read and write files, manage file streams, and interact with the file system in various ways. This article will guide you through the essential concepts and usage of F# IO.

Throughout this lesson, we will cover the process of reading input from the console when working with the stdin object, how to read and write files when working with the System.IO.File module, and how to format and print output to the console when using the printfn function.

Core.Printf Module

To write to the console, we have used a combination of the printf and printfn functions.

Apart from these functions, the Core.Printf module of F# is also equipped with a variety of other methods which can be used to print and format by using placeholders such as % markers.

Below is a table with a brief description of each of the methods listed:

Format Specifications

When working with F# IO, it is important to specify the input and output formats using a format specification that meets your programming needs.

To indicate that a string is a placeholder for a format, a % marker is used in the string.

The format placeholder is written in a specific syntax that includes a percentage symbol followed by a character that specifies the type of format.

For example, %d is used for integer format, %f is used for floating-point format, %s is used for string format, and so on.

The format placeholders can also include additional options that define the width, alignment, and precision of the value being formatted. For example, %5d specifies that the integer value should be formatted with a minimum width of 5 characters, while %-10s specifies that the string value should be formatted with a minimum width of 10 characters and left-aligned.

By using these format specifications, you can ensure that your input and output values are properly formatted according to your desired format and display requirements.

Syntax

%[flags][width][.precision][type]

Types are interpreted as follows:

A width parameter can be used as an optional parameter.

The minimal width of the result is an integer indicating the size of the result at the most minimal level.

As an example, %5d prints an integer with at least 5 characters of spaces between each digit.

Below is a table that describes the valid flags that should be set:

mrexamples - FSharp
mrexamples
- FSharp
Hello, from mrexamplesa: 115.098000
b: 232.768000
c: 115.098
d: 232.768
e: 1.150980e+002
f: 2.327680e+002
False: false

What's your name? John
Hello, John
Greetings from mrexamples
|2023-Apr-11|

Enter your name:
John
Enter your age:
24
Enter your gender:
male
Hello, John!
Your age is: 24.
And your gender is: male.

Example Explanation:

We wrote this code in F# to provide a simple console application that takes user input for name, age, and gender, and displays the output with a greeting message.

We start with an open statement for the System module, which is used to access the Console module for reading input and displaying output.

We define the getUserInput() function to read user input for name, age, and gender using the Console.ReadLine() function, which reads a line of text from the standard input. The values are then stored in the name, age, and gender variables, and a tuple (name, age, gender) is returned.

We define the displayOutput() function to take the name, age, and gender as input arguments and display them using the printfn function, which is used to format and display output to the console. The %s placeholders are used to format the string with the values of name, age, and gender.

In the main function, which is the entry point of the program denoted by the [<EntryPoint>] attribute, we call the getUserInput() function to get user input, and then call the displayOutput() function with the retrieved values. Finally, we return 0, indicating a successful program execution.

Hello Developers,
Welcome to mrexamples!