• Use the &1,… notation to rewrite the following.

  • Enum.map [1,2,3,4], fn x -> x + 2 end
  • Enum.each [1,2,3,4], fn x -> IO.puts x end

iex(1)> Enum.map [1,2,3,4], &1 + 2
[3, 4, 5, 6]

iex(2)> Enum.each [1,2,3,4], IO.puts(&1)
1
2
3
4
:ok

  

The second one doesn’t work for me:

iex(32)>  Enum.each [1,2,3,4], IO.puts(&1)
** (FunctionClauseError) no function clause matching in IO.puts/2
    /private/tmp/elixir-JhMW/elixir-0.10.2/lib/elixir/lib/io.ex:120: IO.puts(#PID<0.36.0>, 1)
    /private/tmp/elixir-JhMW/elixir-0.10.2/lib/elixir/lib/enum.ex:351: Enum."-each/2-lists^foreach/1-0-"/2
    /private/tmp/elixir-JhMW/elixir-0.10.2/lib/elixir/lib/enum.ex:351: Enum.each/2
    erl_eval.erl:569: :erl_eval.do_apply/6
    src/elixir.erl:138: :elixir.eval_forms/3

It seems that IO.puts doesn’t work with Intergers:

iex(32)> IO.puts 1
** (FunctionClauseError) no function clause matching in IO.puts/2
    /private/tmp/elixir-JhMW/elixir-0.10.2/lib/elixir/lib/io.ex:120: IO.puts(#PID<0.36.0>, 1)
    erl_eval.erl:569: :erl_eval.do_apply/6
    src/elixir.erl:138: :elixir.eval_forms/3

Possible fix:

Pass a string, instead of a Integer, to IO.puts.

Enum.each [1,2,3,4], fn x -> IO.puts "#{x}" end

My environment: Erlang R16B01 (erts-5.10.2) [source-bdf5300] [64-bit] [smp:2:2] [async-threads:10] [hipe] [kernel-poll:false] Interactive Elixir (0.10.2-dev)

AC

the possible solution suggested, even with adjusting for the error with puts and integers doesn’t work:

iex> Enum.each 1..4, IO.puts("#{&1}")
** (ArgumentError) argument error
:erl_eval.expr/3

this works though:

iex> Enum.each [1,2,3,4], &IO.puts("#{&1}")
1
2
3
4
:ok

Elixir 0.10.2

iex> Enum.map [1,2,3,4], IO.inspect(&1)
1
2 
3 
4 
[1,2,3,4] 

iex> Enum.map [1, 2, 3, 4], &IO.inspect/1
1
2
3
4
[1, 2, 3, 4]

Elixir 0.12.2

Enum.map [1,2,3,4], &(&1 + 2)

Enum.each [1,2,3,4], &(IO.puts(&1))

In the book you refer to IO.inspect, while here you refer to IO.puts, I guess you should change the suggested solution to match the exercise as shown in the book

Elixir 0.15.1

Enum.map [1, 2, 3, 4], &(&1 + 2)

Enum.each [1, 2, 3, 4], &IO.inspect/1

Elixir v1.1

I was quite proud of my combination solution:

[1, 2, 3, 4]
 |> Enum.map(&(&1 + 2))
 |> Enum.each(&IO.inspect/1)

Getting the hang of those pipes! Although obviously this is a twist on the question, as this isn’t using the fresh list on the each.

v1.2.0

From a file:

first_result = Enum.map [1, 2, 3, 4], &(IO.inspect &1 + 2)

IO.puts first_result

second_result = Enum.each [1,2,3,4], &(IO.inspect &1)

IO.puts second_result

From iex:

Enum.map [1, 2, 3, 4], &(&1 + 2)

Enum.each [1,2,3,4], &(IO.inspect &1) #Dzianis Dashkevich version also works

Those solutions in the original post don’t appear to be valid without the surrounding function context &().

Indeed, in ELixir 1.2 at least they give a CompileError:

IO.puts Enum.map [1,2,3,4], &1 + 2 # CompileError: unhandled &1 outside of a capture

Please correct the text.

So it seems the Elixir 1.2 book has changed to using inspect. Anyways here’s how I did it…

Question: Enum.each [1,2,3,4], fn x -> IO.inspect x end

answer: Enum.each [1,2,3,4], &IO.inspect/1

more rudimentary answer: Enum.each [1,2,3,4], &(IO.inspect(&1))

My solution:

iex(50)> Enum.map [1,2,3,4], &(&1 + 2)      
[3, 4, 5, 6]
iex(51)> Enum.each [1,2,3,4], &(IO.puts(&1))
1
2
3
4
:ok

iex> Enum.map [1,2,3,4], &(&1 + 2)
[3, 4, 5, 6]

iex> Enum.each [1,2,3,4], &IO.inspect/1
1
2
3
4

My solutions… For the first solution is good to create a new function, and pass the reference to Enum.map.

iex> Enum.map [1,2,3,4], &(&1 + 2)

However, for the second function I guess it is better to pass directly the reference to the IO.inspect function instead of giving this task to Elixir (just guessing). Does it make any difference?

iex> Enum.each [1,2,3,4], &IO.inspect/1

Many thanks.

i=&IO.inspect/1
Enum.map [1,2,3,4], i

iex(7)> Enum.map([1,2,3,4], fn x-> x+2 end) == Enum.map([1,2,3,4], &(&1+2))
true
iex(8)> Enum.each([1,2,3,4], fn x-> IO.inspect(x) end) == Enum.each([1,2,3,4], &IO.inspect/1)
1
2
3
4
1
2
3
4
true

So when I enter this (as some of the above posters did):

Enum.each [1,2,3,4] , IO.inspect(&1)

I get the following error: unhandled &1 outside of a capture

I tried that to shorten my original code. My original approach was:

Enum.each [1,2,3,4] , &(IO.inspect(&1) ) Which worked and gave the following output:

1 2 3 4 :ok