Simplifications for Array

[jfmengels]

Seems like we have no simplifications for any Array functions. Don't know how I missed that because there's no work nor issues on that :sweat_smile:

• [x] Array.map #169
• [x] Array.filter #171
• Array.fromList
  • [x] Array.fromList [] -> Array.empty #177
  • [x] Array.toList >> Array.fromList -> identity #190
• Array.toList
  • [x] Array.fromList >> Array.toList -> identity #190
  • [x] Array.toList Array.empty -> [] #234
• Array.isEmpty
  • [x] Array.isEmpty (Array.fromList [x]) -> False
  • [x] Array.isEmpty (Array.fromList []) -> True
  • [x] Array.isEmpty Array.empty -> True
  • [x] Array.isEmpty (Array.repeat 1 x) -> False
  • [x] Array.isEmpty (Array.initialize 1 f) -> False
• Array.repeat
  • [x] Array.repeat 0 x -> Array.empty #179
  • [x] Array.repeat -1 x -> Array.empty #179
  • [x] Array.repeat n x |> Array.toList -> List.repeat n x #234
  • Array.repeat 1 x -> Array.fromList [ x ] (Only when the number is 1) (Good fixes are too inconsistent)
• Array.initialize
  • [x] Array.initialize 0 f -> Array.empty #185
  • [x] Array.initialize -1 f -> Array.empty #185
  • Array.initialize 1 f -> Array.fromList [ f 0 ] (Only when the number is 1) (Good fixes are too inconsistent)
• Array.length
  • [x] Array.length Array.empty -> 0 #191
  • [x] Array.length (Array.fromList [ a, b, c ]) -> 3 #191
  • [x] Array.length (Array.repeat 1 x) -> 1 #191
  • [x] Array.length (Array.initialize 1 f) -> 1 #191
  • [x] Array.length (Array.repeat n x) to max 0 n #191
  • [x] Array.length (Array.initialize n f) to max 0 n #191
  • [x] Array.length (Array.push x (Array.fromList [ a, b, c ])) -> 4
  • [x] Array.length (Array.push x (Array.repeat 3 y)) -> 4 (same for Array.initialize)
  • [ ] Array.length (Array.push x (Array.repeat n y)) -> (Basics.max 0 n) + 1 (same for Array.initialize)
• Array.indexedMap
  • [x] Same as for List.indexedMap #192
• Array.append
  • [x] Array.append Array.empty array -> array #199
  • [x] Array.append array Array.empty -> array #199
  • [x] Array.append (Array.fromList [ a, b, c ]) (Array.fromList [ d, e, f ]) -> Array.fromList [ a, b, c, d, e, f ] #199
  • [ ] Array.append (Array.repeat 2 x) (Array.repeat 3 x) -> Array.repeat 5 x
  • [ ] Array.append (Array.repeat n x) (Array.repeat m x) -> Array.repeat (max 0 n + max 0 m) x
• Array.slice
  • Same as for String.slice #208
• Array.get
  • [x] Array.get n Array.empty -> Nothing #203
  • [x] Array.get -3 array -> Nothing #203
  • [x] Array.get 2 (Array.fromList [ 1, 2, 3 ]) -> Just 3 #203
  • [x] Array.get 100 (Array.fromList [ 1, 2, 3 ]) -> Nothing #203
  • [x] Array.get 2 (Array.repeat 10 x) -> Just x #252
  • [x] Array.get 100 (Array.repeat 10 x) -> Nothing #252
  • [x] Array.get 2 (Array.initialize 10 f) -> Just (f 2) #252
  • [x] Array.get 100 (Array.initialize 10 f) -> Nothing #252
  • [ ] Array.get n (Array.repeat n x) -> Nothing
  • [ ] Array.get n (Array.initialize n f) -> Nothing
  • [ ] Array.get 1 (Array.push x <| Array.push y array) -> Just y
• Array.set
  • [x] Array.set n x Array.empty -> Array.empty #207
  • [x] Array.set 1 x (Array.fromList [ 1, 2, 3 ]) -> Array.fromList [ 1, x, 3 ] #207
  • [x] Array.set 100 x (Array.fromList [ 1, 2, 3 ]) -> Array.fromList [ 1, 2, 3 ] #207
  • [x] Array.set -3 x array -> array #207
  • [ ] Array.set 100 x (Array.repeat 10 y) -> Array.repeat 10 y
  • [ ] Array.set 100 x (Array.initialize 10 f) -> Array.initialize 10 f
• Array.push
  • [ ] Array.push x Array.empty -> Array.fromList [ x ]
  • [ ] Array.push x (Array.fromList [ a, b, c ]) -> Array.fromList [ a, b, c, x ]
  • [ ] Array.push x (Array.repeat n x) -> Array.repeat (max 0 n + 1) x
• Array.foldl and Array.foldr
  • [x] Array.foldr f x Array.empty -> x #231
  • [x] Same as other List fold operations #231
• Array.toIndexedList
  • [x] Array.toIndexedList Array.empty -> [] #232
  • [x] array |> Array.toIndexedList |> List.map Tuple.second to array |> Array.toList #232
  • [ ] array |> Array.toIndexedList |> List.map Tuple.first to List.range 0 (Array.length array - 1)

Leave a comment if I missed something :)

---

(I'll probably move this to another issue when I have time) We could also do simplifications across types:

-- Since we do
Array.repeat 3 x
  |> Array.length
--> 3

-- we could also do
Array.repeat 3 x
  |> Array.toList
  |> List.length
--> 3

[lue-bird]

A super nice set of checks (I love the get and length checks).

Maybe

Array.fromList []
--> Array.empty

array |> Array.toIndexedList |> List.map Tuple.second
--> array |> Array.toList

Array.repeat 1 x
--> Array.fromList [ x ]

And for Array.slice I think we can just copy the fixes we already have for String.slice which also allows negative indexes

[jfmengels]

I was a little torn on

Array.repeat 1 x
--> Array.fromList [ x ]

but I guess it is a lot more idiomatic, so let's do it, yes. I'll also add

Array.initialize 1 f
--> Array.fromList [ f x ]

[lue-bird]

I think you meant

Array.initialize 1 f
--> Array.fromList [ f 0 ]

[lue-bird]

The suggested check

Array.append (Array.repeat n x) (Array.repeat m x)
--> Array.repeat (n + m) x (if n and m are literals, add them up directly)

Only works if we know them as literals and neither is negative. E.g.

let m = -1
in
Array.append (Array.repeat 2 x) (Array.repeat m x)
--> Array.repeat 0 x

would be wrong. (The correct result in this case is Array.repeat 2 x)

Equally,

Array.push x (Array.repeat n x)
--> Array.repeat (n + 1) x (if n is a literal, just increment it)

Only works if we know n as a non-negative literal. E.g.

let n = -1
in
Array.push x (Array.repeat n x)
--> Array.repeat 0 x

would be wrong. (The correct result in this case is Array.push x Array.empty)

[jfmengels]

All good points :+1: Should we also do Array.push x Array.empty --> Array.fromList [ x ]? It's more idiomatic, though I suspect the former to be faster, but also by only a tiny amount. (And by that logic we should not fix 1 :: [] to [ 1 ])

[jfmengels]

Should we simplify Array.length (Array.repeat n x) to max 0 n? It's not the prettiest fix but it's quite a bit simpler and definitely more performant.

[jfmengels]

I added Array.repeat n x |> Array.toList -> List.repeat n x

[jfmengels]

I added Array.get n (Array.repeat n x) -> Nothing (and same for initialize)

[morteako]

array |> Array.toIndexedList |> List.map Tuple.first to List.range 0 (List.length array - 1)

should probably be

array |> Array.toIndexedList |> List.map Tuple.first to List.range 0 (Array.length array - 1)