pillaiindu
Using a map after do: in a list comprehension
These two work:
iex(1)> for {key, val} <- %{"a" => 1, "b" => 2}, do: {key, val * val}
[{"a", 1}, {"b", 4}]
iex(2)> for {key, val} <- %{"a" => 1, "b" => 2}, into: %{}, do: {key, val * val}
%{"a" => 1, "b" => 4}
But this one gives syntax error:
iex(3)> for {key, val} <- %{"a" => 1, "b" => 2}, do: %{key, val * val}
** (SyntaxError) iex:3:62: syntax error before: '}'
|
3 | for {key, val} <- %{"a" => 1, "b" => 2}, do: %{key, val * val}
| ^
Why?
Why can’t we use map directly after the do: in list-comprehensions?
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Kurisu
I think you have a synthax error on the way you’re trying to define the map. It is not about the for or do.
One way you could achieve the map definition would be :
%{“#{key}”: val * val}
or
%{“#{key}” => val * val}
eksperimental
pillaiindu
Yes, it’s a tuple not a map, and not even a tuple, because tuple doesn’t have %{. 
I did it accidentally and it took time to catch the mistake. I wanted to see if someone else can catch the mistake, because the error message doesn’t specifically point it out.
%{"#{ isn’t even needed, using key directly works.
for {key, val} <- %{"a" => 1, "b" => 2}, do: %{key => val * val} works.
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