Visual F# 100 Examples: Example 14 and 15(Pattern Matching)

Pattern matching/match with statement is similar to the switch selection statement in other programming languages. The following examples demonstrate how to use it:


Problem: Make an application that will asks a letter and displays its equivalent U. S. military phonetic alphabet.

//use F# library
open System
//change the CLI title
System.Console.Title<-"Display Military Phoenitic Alphabet"
//adds color to our console application
System.Console.ForegroundColor<-ConsoleColor.Blue
//asks the user to enter a letter
printfn "Enter a letter:"
//convert the input to character and convert it to uppercase letter
//this is just for comparison purpose
let chrletter=Char.ToUpper(Convert.ToChar(System.Console.ReadLine()))
//clear the screen   
System.Console.Clear()
//match the value of chrletter to the ff. values
match chrletter with
//if the value of chrletter is a or A display Alpha
| 'A' ->printfn "Alpha"
//if the value of chrletter is b or B display Bravo
| 'B' ->printfn "Bravo"
//if the value of chrletter is c or C display Charlie
| 'C' ->printfn "Charlie"
//if the value of chrletter is d or D display Delta
| 'D' ->printfn "Delta"
//if the value of chrletter is e or E display Echo
| 'E'->printfn "Echo"
//if the value of chrletter is f or F display Foxtrot
| 'F'->printfn "FoxTrot"
//if the value of chrletter is g or G display Golf
| 'G'->printfn "Golf"
//if the value of chrletter is h or H display Hotel
| 'H'->printfn "Hotel"
//if the value of chrletter is i or I display India
| 'I'->printfn "India"
//if the value of chrletter is j or J display Juliet
| 'J'->printfn "Juliet"
//if the value of chrletter is k or K display Kilo
| 'K'->printfn "Kilo"
//if the value of chrletter is l or L display Lima
| 'L'->printfn "Lima"
//if the value of chrletter m or M display Mike
| 'M'->printfn "Mike"
//if the value of chrletter is n or N display November
| 'N'->printfn "November"
//if the value of chrletter is o or O display Oscar
| 'O'->printfn "Oscar"
//if the value of chrletter is p or P display Papa
| 'P'->printfn "Papa"
//if the value of chrletter is q or Q display Quebec
| 'Q'->printfn "Quebec"
//if the value of chrletter is r or R display Romeo
| 'R'->printfn "Romeo"
//if the value of chrletter is s or S display Sierra
| 'S'->printfn "Sierra"
//if the value of chrletter is t or T display Tango
| 'T'->printfn "Tango"
//if the value of chrletter is u or U display Uniform
| 'U'->printfn "Uniform"
//if the value of chrletter is v or V display Victor
| 'V'->printfn "Victor"
//if the value of chrletter is w or W display Whiskey
| 'W'->printfn "Whiskey"
//if the value of chrletter is x or X display X-Ray
| 'X'->printfn "X-Ray"
//if the value of chrletter is y or Y display Yankee
| 'Y'->printfn "Yankee"
//if the value of chrletter is z or Z display Zulu
| 'Z'->printfn "Zulu"
//otherwise
| _ ->printfn "Invalid input"

The last statement |_ is similar to the
default statement in other programming languages Switch conditional structure. It is automatically executed when no pattern match is found. Don't forget to add it at the end of every match with statement otherwise you will get an “Incomplete pattern matches on this expression” error.


Problem: Make an application that will ask the month number and display the corresponding month name and the number of days in it. Use pattern matching.

//use F# library
open System
//change the CLI title
System.Console.Title<-"Display Month Name"
//adds color to our console application
System.Console.ForegroundColor<-ConsoleColor.Blue
System.Console.BackgroundColor<-ConsoleColor.White
//asks the user to enter a month number
printfn "Enter a month number(1-12):"
let intmonth=Convert.ToInt32(System.Console.ReadLine())
//clear the screen   
System.Console.Clear()
//match the value of intmonth to the ff. values
match intmonth with
//if the value of intmonth is 1 display January
| 1 ->printfn "January(31 days)"
//if the value of intmonth is 2 display February
| 2 ->printfn "Febrary(28/29 days)"
//if the value of intmonth is 3 display March 
| 3 ->printfn "March(31 days)"
//if the value of intmonth is 4 display April
| 4 ->printfn "April(30 days)"
//if the value of intmonth is 5 display May
| 5 ->printfn "May(31 days)"
//if the value of intmonth is 6 display June
| 6 ->printfn "June(30 days)"
//if the value of intmonth is 7 display July
| 7 ->printfn "July(31 days)"
//if the value of intmonth is 8 display August
| 8 ->printfn "August(31 days)"
//if the value of intmonth is 9 display September
| 9 ->printfn "September(30 days)"
//if the value of intmonth is 10 display October
| 10 ->printfn "October(31 days)"
//if the value of intmonth is 11 display November
| 11 ->printfn "November(30 days)"
//if the value of intmonth is 12 display December
| 12->printfn "December(31 days)"
//otherwise
| _ ->printfn "Invalid input"

That's all for now my Visual F# friends. Ciao!