Constructing a simple tree with ASCII in F#

This is just a basic HackerRank challenge I was working on to better understand F#. Its purpose is just to print a tree that has a straight 'trunk' of \$n\$, splits into 2 branches which diverge to \$n\$, then branches grow a straight trunk to \$\frac{n}{2}\$ which split and diverge to \$\frac{n}{2}\$, etc.

(Note: I was told to avoid using variables if possible, so the only one I used was to store the iterations which are meant to be \$n \le 5\$.)

```
[]
let main argv =

let iterations = System.Convert.ToInt32(System.Console.ReadLine())

//63 rows
//100 cols
//16 length

let splitRoots = fun x -> Array.collect (fun elem -> [|elem-1;elem+1|]) x

let isEven = fun i -> if i % 2 = 0 then true else false

let advanceBranch = fun x -> Array.mapi (fun i elem -> if isEven i then elem-1 else elem+1) x

let treeLine = fun oneLocs w ->
String.concat "" (Seq.map (fun x -> if Array.exists (fun elem -> elem = x) oneLocs then "1" else "_") w)

//if trunk and counter > 0 --> write more trunk
//if trunk and counter = 0 --> split and transition to branch
//if branch and counter > 0 --> write more branch
//if branch and counter = 0 --> transition to trunk and deecrement max
let rec tree = fun l w h max original counter branch roots acc ->
match branch with
| _ when max = 0 ->
acc
| false when counter > 0 ->
tree l w h max original (counter-1) false roots (acc @ [ treeLine roots (seq { 1 .. w }) ])
| false when counter = 0 ->
tree l w h max original (original-1) true (splitRoots roots) acc
| true when counter > 0 ->
tree l w h max original (counter-1) true (advanceBranch roots) (acc @ [ treeLine roots (seq { 1 .. w })])
| true when counter = 0 ->
tree l w h (max-1) (original/2) (original/2) false roots (acc @ [ treeLine roots (seq { 1 .. w }) ])

let emptyRow = String.concat "" (Seq.map (fun x

There's a couple of simple things you can do to reduce the clutter in your code. For example, this:

let isEven = fun i -> if i % 2 = 0 then true else false

Firstly,

if someCondition then true else false

can always be written simply as

someCondition

You're also missing a trick with your declaration:

let someFunction = fun i -> ...

Can simply be written as

let someFunction i = ...

So your isEven function is simply:

let isEven i = i % 2 = 0

I'm coming back to F# after a long break (2+ years) so I'm not going to suggest anything else as I'm still relearning!

Edit:

Actually...

let emptyRow = String.concat "" (Seq.map (fun x -> "_") (seq{ 1..100}))

Is simply:

let emptyRow = String.replicate 100 "_"

StackExchange Code Review Q#113273, answer score: 2