CODEWITHSUNDEEP
elixir
Datsik
Datsik

Reputation: 14824

How do you properly pipe (chain) functions with callbacks

I'm trying to do this exercise from this book I'm learning from.

The goal is to read a bunch of words from a random .txt file (Which is supplied) and then find all words that start with D, and capitalize those words and return only them. This is what I have so far:

defmodule ReadFile do
    def findD(contents) do
        newArray = Enum.filter(contents, (word -> String.starts_with?(word, "D")))
        |> Enum.map (word -> String.upcase(word))
    end
end

I feel like in theory this should work just fine, but it doesn't seem to. Any information would be fantastic thanks.

I'm trying to use Filter the way I find it in the Elixir Docs:

filter(t, (element -> as_boolean(term))) :: list

This is my error:

listTest.exs:1: warning: redefining module ReadFile

== Compilation error on file listTest.exs ==
** (CompileError) listTest.exs:3: unhandled operator ->
    (stdlib) lists.erl:1353: :lists.mapfoldl/3
    (stdlib) lists.erl:1354: :lists.mapfoldl/3

** (exit) shutdown: 1
    (elixir) lib/kernel/parallel_compiler.ex:202: Kernel.ParallelCompiler.handle_failure/5
    (elixir) lib/kernel/parallel_compiler.ex:185: Kernel.ParallelCompiler.wait_for_messages/8
    (elixir) lib/kernel/parallel_compiler.ex:55: Kernel.ParallelCompiler.spawn_compilers/3
       (iex) lib/iex/helpers.ex:168: IEx.Helpers.c/2

Upvotes: 0

Views: 773

Answers (1)

NoDisplayName
NoDisplayName

Reputation: 15736

You have some mistakes in the function syntax, the right one would be this:

contents
|> Enum.filter(fn(word) -> String.starts_with?(word, "D") end)
|> Enum.map(fn(word) -> String.upcase(word) end)

Also, please, read the getting started guide.

Upvotes: 2

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