elm-lazy-list drop benchmark

.gitignore

elm-stuff/

chrome.png

elm-package.json

{
    "version": "1.0.0",
    "summary": "helpful summary of your project, less than 80 characters",
    "repository": "https://github.com/user/project.git",
    "license": "BSD3",
    "source-directories": [
        "."
    ],
    "exposed-modules": [],
    "dependencies": {
        "BrianHicks/elm-benchmark": "2.0.3 <= v < 3.0.0",
        "eeue56/elm-lazy": "1.0.0 <= v < 2.0.0",
        "eeue56/elm-lazy-list": "1.0.0 <= v < 2.0.0",
        "elm-lang/core": "5.1.1 <= v < 6.0.0",
        "elm-lang/html": "2.0.0 <= v < 3.0.0"
    },
    "elm-version": "0.18.0 <= v < 0.19.0"
}

firefox.png

Main.elm

module Main exposing (..)

import Benchmark exposing (..)
import Benchmark.Runner exposing (BenchmarkProgram, program)
import Lazy exposing (Lazy)
import Lazy.List exposing (LazyList)


{-| Comparing the replacement `drop` with the original, performance-wise
-}
suite : Benchmark
suite =
    let
        testList =
            Lazy.List.numbers

        numberToDrop =
            500

        -- much more than this and chrome stackoverflows with the lib version
    in
    describe "Lazy.List"
        [ Benchmark.compare "drop"
            "library"
            (\_ ->
                Lazy.List.drop numberToDrop testList
                    |> Lazy.List.head
            )
            "replacement"
            (\_ ->
                customDrop numberToDrop testList
                    |> Lazy.List.head
            )
        ]


{-| Replacement for `Lazy.List.drop`
The original `Lazy.List.drop` fails causes a stackoverflow when dropping too many elements because the recursion cannot be optimized away. This new version uses an inner function which can be optimized and, as far as I can tell, eliminates the change of stack overflows at least in this department.
-}
customDrop : Int -> LazyList a -> LazyList a
customDrop num list =
    let
        dropHelper num list =
            if num <= 0 then
                Lazy.force list
            else
                case Lazy.force list of
                    Lazy.List.Nil ->
                        Lazy.List.Nil

                    Lazy.List.Cons _ rest ->
                        dropHelper (num - 1) rest
    in
    Lazy.lazy
        (\() ->
            dropHelper num list
        )


main : BenchmarkProgram
main =
    program suite

safari.png