How to translate this Erlang code to LFE?

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1

Hello everyone,

I have been trying to solve AOC with LFE, yet there is something I don’t understand.

This is the Erlang code…

-module(day6).
-export([load_data/0]).

load_data() ->
    {ok, Bin} = file:read_file("input.txt"),
    List = binary:split(string:trim(Bin), <<",">>, [global, trim]),
    lists:map(fun(X) -> 
        {V, _} = string:to_integer(X), 
        V 
    end, List).

and this almost the same in LFE

(defmodule day6 (export (load_data 0)))

(defun load_data ()
    (let 
        (((tuple 'ok bin) (file:read_file "input.txt"))) 
        (lists:map 
            (lambda (x) (string:to_integer x))
            (string:split (string:trim bin) "," 'all))))

I cannot figure how to replace this

    fun(X) -> 
        {V, _} = string:to_integer(X), 
        V 
    end

and this would be the LFE code.

(lambda (x) (string:to_integer x))

but string:to_integer x returns a tuple, and I am only interested in the first value.

How can I return only the first element?

Thanks for taking time.

2 Likes
2

Sorry for the question… I just found the solution after posting.

(defun load_data ()
    (let 
        (((tuple 'ok bin) (file:read_file "input.txt"))) 
        (lists:map 
            (lambda (x) (let (((tuple y _) (string:to_integer x))) y))
            (string:split (string:trim bin) "," 'all))))

It is working as expected. I did not fully understood the let macro :slight_smile:

2 Likes
3

My lfe skills are not great but can’t you just let bind the value, just as you do for your file:read_file?

(lambda (x) 
  (let (((tuple v _) (string:to_integer x)))
  v))

Or you could use element/2

(lambda (x) (element 1 (string:to_integer x)))

EDIT: Oops, late to the party :smiley:

4 Likes
4

Thank You for your reply, I figure it out also, I have to say it’s my first Lisp code :slight_smile:

3 Likes
5

All I can say here is that the solutions are correct.

7 Likes
6

Congrats Koko! :023:

I hope to learn a Lisp one day… and I think LFE would be perfect :smiley: if we see a PragProg book from Duncan (or Robert) I will add it further up my list :003:

2 Likes
7

Since then I made an AOC problem with LFE.

I have read the books from @oubiwann and followed the start of this course.

Here is the secret I have learned :slight_smile:

# Elixir
input |> ... |> ... |>

%% Erlang
S0=...(Input).
S1=...(S0).
S3=...(S1).

; LFE
(...(...(...input)))
3 Likes
8

@oubiwann has written a lot of great stuff for/about/using LFE.

3 Likes
9

There is also Clojures threading:

(-> input
  (s0)
  (s1)
  (s2)

Clojure macros are available in LFE as import.

4 Likes