Some F# Samples by Michael Hartmann

Finding the maximal value in a list of integers coded "C# style"

  open List
  open Printf


  let data = [1; 2; 3; 8; 6; 5]


  let rec list_max plist =
    if length plist < 1 then failwith "empty list" else   // empty list: fail 
    if length plist = 1 then (List.hd plist) else         // single element list: return the element 
    max (List.hd plist)(list_max (List.tl plist))         // multiple element list: recursive case


  do printf "result = %d\n" (list_max data)

Finding the maximal value in a list of integers coded "F# style"

  open List
  open Printf


  let data = [1; 2; 3; 3; 4; 5]
  let rec max_of_list plist =
    match plist with
    | [] -> failwith "empty list"                     // empty list: fail
    | [x] -> x                                        // single element list: return the element
    | x::tail -> max x (max_of_list tail)             // multiple element list: recursive case


  do printf "result = %d\n" (max_of_list data)

Applying a function twice

  open List
  open Printf


  let double z = 2 * z


  let apply f y = f(y)
  let applytwice f y = f(f(y))


  do printf "result = %d\n" (apply double 5)
  do printf "result = %d\n" (applytwice double 5)
  do printf "result = %d\n" (apply double (apply double 5))

Some simple array manipulations, using the MLLib Array module

  open Printf


  // just some declarations for arrays 


  // creates an F# matrix ... 
  let a = Array.create_matrix 4 4 6;;


  // ... same but with explicit type declaration for the return value 
  let (b : int array array) = Array.create_matrix 4 4 6;;


  // One way to print first vector of matrix a 
  do Array.map (fun i -> printf "%d\n" i) a.(1)
  do printf "next\n"


  // print element 1,2 of matrix a 
  do printf "a[1,2] = %d\n" (string_of_int a.(1).(2))
  do printf "done"

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