What does this F# code look like in Erlang – Part 4 of N

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Here I will look at how some commonly used functions in F#’s List module might be translated to Erlang using Erlang’s equivalent – the lists module.

 

List.append

F#:         let newList = List.append [ 1..5 ] [ 6..10 ]

Erlang:   NewList = lists:append([ 1, 2, 3, 4, 5 ], [ 6, 7, 8, 9, 10 ]).

List.average

F#:         let avg = List.average [ 1.0..10.0 ]

Erlang:   List = lists: seq(1, 10).

             Avg = lists: sum(List) / length(List).

List.collect

F#:         let duped = [ ‘a’; ‘b’; ‘c’ ] |> List.collect (fun x -> [ x; x ])

Erlang:   Duped = lists:flatmap(fun(X) –> [ X, X ] end, [ a, b, c ]).

List.concat

F#:         let newList = List.concat [ [ 1; 2 ]; [ 3; 4; 5 ]; [ 6; 7; 8; 9 ] ]

Erlang:   NewList = lists:append([ [ 1, 2 ], [ 3, 4, 5 ], [ 6, 7, 8, 9 ] ]).

 

List.exists

F#:         let hasEven = [ 1..2..9 ] |> List.exists (fun x -> x % 2 = 0)

Erlang:   HasEven = lists:any(fun(X) -> X rem 2 =:= 0 end, lists: seq(1, 9, 2)).

 

List.filter

F#:         let evens = [ 1.. 6 ] |> List.filter (fun x -> x % 2 = 0)

Erlang:   Evens = lists:filter(fun(X) -> X rem 2 =:= 0 end, lists:seq(1, 6)).

 

List.find

F#:         let fstMatch = [ "cui"; "xue"; "yan" ] |> List.find ((=) "yan")

Erlang:   FstMatch = lists:keyfind(yan, 1, [ { cui }, { xue }, { yan } ]).

 

List.fold

F#:         let data = [ ("Cats", 4); ("Dogs", 5); ("Mice", 3); ("Elephants", 2) ]

              let count = data |> List.fold (fun acc (_, x) -> acc + x) 0

Erlang:   Data = [ { cats, 4 }, { dogs, 5 }, { mice, 3 }, { elephants, 2 } ].

             Count = lists:foldl(fun({ _, N }, Acc) -> Acc + N end, 0, Data).

 

List.foldBack

F#:         let copy = List.foldBack (fun elem acc -> elem::acc) [ 1..10 ] []

Erlang:   Copy = lists:foldr(fun(X, Acc) -> [X|Acc] end, [], lists:seq(1, 10)).

 

List.forall

F#:         let allEven = [2; 4; 6; 8] |> List.forall (fun n -> n % 2 = 0)

Erlang:   AllEven = lists:all(fun(X) -> X rem 2 =:= 0 end, [ 2, 4, 6, 8 ]).

 

List.iter

F#:         [1..10] |> List.iter (printfn "%d")

Erlang:   lists:foreach(fun(X) -> io:format("~p~n", [ X ]) end, lists:seq(1, 10)).

 

List.length

F#:         let lst = [ 1..10 ]

              // you can call the Length property on a list

              let len1 = lst.Length

              // or use List.length

              let len2 = List.length lst

Erlang:   Lst = lists: seq(1, 10).

             % you can use the length built-in function

             Len1 = length(Lst).

             % or you can use lists:flatlength

             Len2 = lists:flatlength(Lst).

 

List.map

F#:         let doubles = [ 1..10 ] |> List.map (fun x -> x * 2)

Erlang:   Doubles = lists:map(fun(X) -> X * 2 end, lists:seq(1, 10)).

 

List.max

F#:         let max = [ 1..10 ] |> List.max

Erlang:   Max = lists:max(lists: seq(1, 10)).

 

List.min

F#:         let min = [ 1..10 ] |> List.min

Erlang:   Min = lists:min(lists: seq(1, 10)).

 

List.nth

F#:         let fourth = List.nth [ 1..10 ] 3

Erlang:   Fourth = lists:nth(4, lists: seq(1, 10)). % node that n is not zero-indexed here!

 

List.partition

F#:         let evens, odds = [ 1..10 ] |> List.partition (fun n -> n % 2 = 0)

Erlang:   { Evens, Odds } = lists:partition(fun(X) -> X rem 2 =:= 0 end, lists:seq(1, 10)).

 

List.rev

F#:         let rev = [ 1..10 ] |> List.rev

Erlang:   Rev = lists:reverse(lists: seq(1, 10)).

 

List.sort

F#:         let sorted = List.sort [ 1; 4; 7; -1; 5 ]

Erlang:   Sorted = lists:sort([ 1, 4, 7, -1, 5 ]).

 

List.sum

F#:         let sum = List.sum [ 1..10 ]

Erlang:   Sum = lists:sum(lists:seq(1, 10)).

 

List.unzip

F#:         let lstA, lstB = List.unzip [ (1, 2); (3, 4) ]

Erlang:   { LstA, LstB } = lists:unzip([ {1, 2}, {3, 4} ]).

 

List.zip

F#:         let lst = List.zip [ 1; 2 ] [ 3; 4 ]

Erlang:   Lst = lists:zip([ 1, 2 ], [ 3, 4 ]).

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Yan Cui

I’m an AWS Serverless Hero and the author of Production-Ready Serverless. I have run production workload at scale in AWS for nearly 10 years and I have been an architect or principal engineer with a variety of industries ranging from banking, e-commerce, sports streaming to mobile gaming. I currently work as an independent consultant focused on AWS and serverless.

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