Week 1 - Functional Programming

module Program

open System

let inc = fun x -> x + 1
let abs = fun x -> if x >= 6 then x else -x

let rec addTo =
    fun n ->
        if n = 0 then
            0
        else
            n + (addTo (n - 1))

//! There is another syntax for writing addTo
let rec addToAlt n =
    if n = 0 then
        0
    else
        n + (addTo (n - 1))

// Part 4 -  Making an operator, mind the order in math * before +
let (>==) = fun x y -> x + y * x

//TODO: Exercise 1
let rec allNumber n =
    if n = 0 then
        "0"
    else
        (allNumber (n - 1)) + " " + (string n)

// TODO: Exercise 2
let rec allNumberRev n =
    if n = 0 then
        "0"
    else
        (string n) + " " + (allNumberRev (n - 1))

// TODO: Exercise 3
let rec allNumberRange l h =
    if l = h + 1 then
        ""
    else
        (string l) + " " + (allNumberRange (l + 1) h)

// TODO: Exercise 4
let rec allNumberRangeRev l h =
    if l = h then
        (string l)
    else
        (allNumberRangeRev (l + 1) h) + " " + (string l)

// TODO: Exercise 5
let rec allEvenRange lower upper =
    if lower = upper then
        if lower % 2 = 0 then
            (string lower)
        else
            ""
    else
        let current =
            if lower % 2 = 0 then
                (string lower)
            else
                ""
        current + " " + (allEvenRange (lower + 1) upper)

// TODO: Exercise 6
let rec drawLine n =
    if n = 0 then
        ""
    else
        (drawLine (n - 1)) + "*"

// TODO: Exercise 7
let rec drawSymbols char length =
    if length = 0 then
        ""
    else
        (drawSymbols char (length - 1)) + char

// TODO: Exercise 8
let rec toBinary n =
    if n < 0 then
        "Incorrect parameter."
    else
        if n = 0 then
            ""
        else
            (toBinary (n / 2)) + (string (n % 2))

// TODO: Exercise 9
//! Don't understand the question..

[<EntryPoint>]
let main argv =
    printfn "Running the program.."

    //* Part 1
    let resBig = (fun x -> x + 1) 1
    // Same as
    let res = inc 1
    printfn "%d" resBig
    printfn "%d" res

    //* Part 2
    let num = abs 5
    let num2 = abs -10
    printfn "abs func %d and %d" num num2

    //* Part 3
    let add = addTo 5
    let addalt = addToAlt 10
    printfn "the addTo func %d and the addToAlt func %d" add addalt

    //* Part 4 - Operator
    let op = 5 >== 3
    printfn "My result is %d" op

    printfn "\n\n----Exercises ------------------------\n\n"

    let exercise n =
        printfn "Exercise %d" n

    //TODO: Exercise 1
    exercise 1
    let num = allNumber 10
    printfn "My result is %s" num
    printfn "\n"

    //TODO: Exercise 2
    exercise 2
    let num = allNumberRev 10
    printfn "My result is %s" num
    printfn "\n"

    //TODO: Exercise 3
    exercise 3
    let num = allNumberRange 16 23
    printfn "My result is %s" num
    printfn "\n"

    //TODO: Exercise 4
    exercise 4
    let num = allNumberRangeRev 16 23
    printfn "My result is %s" num
    printfn "\n"

    //TODO: Exercise 5
    exercise 5
    let num = allEvenRange 4 10
    printfn "My result is %s" num
    printfn "\n"

    //TODO: Exercise 6
    exercise 6
    let line = drawLine 10
    printfn "My result is %s" line
    printfn "\n"

    //TODO: Exercise 7
    exercise 7
    let line = drawSymbols "&" 5
    printfn "My result is %s" line
    printfn "\n"

    //TODO: Exercise 8
    exercise 8
    let num = toBinary 34
    printfn "My result is %s" num
    printfn "\n"

    //TODO: Exercise 9
    //! Don't understand the question..

    0 // return an integer exit code