How to code Fizzbuzz in F#

Question

I am currently learning F# and have tried (an extremely) simple example of FizzBuzz.

This is my initial attempt:

for x in 1..100 do 
    if x % 3 = 0 && x % 5 = 0 then printfn "FizzBuzz"  
    elif x % 3 = 0 then printfn "Fizz"
    elif x % 5 = 0 then printfn "Buzz"
    else printfn "%d" x

What solutions could be more elegant/simple/better (explaining why) using F# to solve this problem?

Note: The FizzBuzz problem is going through the numbers 1 to 100 and every multiple of 3 prints Fizz, every multiple of 5 prints Buzz, every multiple of both 3 AND 5 prints FizzBuzz. Otherwise, simple the number is displayed.

Thanks :)

Answer 1

I think you already have the "best" solution.

If you want to show off more functional/F#-isms, you could do e.g.

[1..100] 
|> Seq.map (function
    | x when x%5=0 && x%3=0 -> "FizzBuzz"
    | x when x%3=0 -> "Fizz"
    | x when x%5=0 -> "Buzz"
    | x -> string x)
|> Seq.iter (printfn "%s")

and use lists, sequences, map, iter, patterns, and partial application.

[1..100]    // I am the list of numbers 1-100.  
            // F# has immutable singly-linked lists.
            // List literals use square brackets.

|>          // I am the pipeline operator.  
            // "x |> f" is just another way to write "f x".
            // It is a common idiom to "pipe" data through
            // a bunch of transformative functions.

   Seq.map  // "Seq" means "sequence", in F# such sequences
            // are just another name for IEnumerable<T>.
            // "map" is a function in the "Seq" module that
            // applies a function to every element of a 
            // sequence, returning a new sequence of results.

           (function    // The function keyword is one way to
                        // write a lambda, it means the same
                        // thing as "fun z -> match z with".
                        // "fun" starts a lambda.
                        // "match expr with" starts a pattern
                        // match, that then has |cases.

    | x when x%5=0 && x%3=0 
            // I'm a pattern.  The pattern is "x", which is 
            // just an identifier pattern that matches any
            // value and binds the name (x) to that value.
            // The "when" clause is a guard - the pattern
            // will only match if the guard predicate is true.

                            -> "FizzBuzz"
                // After each pattern is "-> expr" which is 
                // the thing evaluated if the pattern matches.
                // If this pattern matches, we return that 
                // string literal "FizzBuzz".

    | x when x%3=0 -> "Fizz"
            // Patterns are evaluated in order, just like
            // if...elif...elif...else, which is why we did 
            // the 'divisble-by-both' check first.

    | x when x%5=0 -> "Buzz"
    | x -> string x)
            // "string" is a function that converts its argument
            // to a string.  F# is statically-typed, so all the 
            // patterns have to evaluate to the same type, so the
            // return value of the map call can be e.g. an
            // IEnumerable<string> (aka seq<string>).

|>          // Another pipeline; pipe the prior sequence into...

   Seq.iter // iter applies a function to every element of a 
            // sequence, but the function should return "unit"
            // (like "void"), and iter itself returns unit.
            // Whereas sequences are lazy, "iter" will "force"
            // the sequence since it needs to apply the function
            // to each element only for its effects.

            (printfn "%s")
            // F# has type-safe printing; printfn "%s" expr
            // requires expr to have type string.  Usual kind of
            // %d for integers, etc.  Here we have partially 
            // applied printfn, it's a function still expecting 
            // the string, so this is a one-argument function 
            // that is appropriate to hand to iter.  Hurrah!