Having problem with list pattern machine in Map

[peerreynders]

See

Pronouncing `<-`

Learn You Some Erlang: List Comprehensions uses “in” - and it does set up the association between ∈ and <- though it isn’t explicit about. Personally I’ve always pronounced ∈ as “element of”. Designing for Scalability with Erlang/OTP p.27 The effect of this is to successively bind the variable X to the values 2, 3, 5, 7, and 11. In other words, it generates the elements from the list: the symbol <- is meant to suggest the “element of” symbol for sets, ∈. Erlang Programming - A Concurrent Ap…

for {_key, value} <- convert_errors do
  IO.inspect value
end

For each tuple {_key, value} which is an element of the collection/enumeration named convert_errors …

{_key, [value]}  =  convert_errors

Match the (single) value named convert_errors with the tuple pattern {_key,[value]} pattern, whereupon a successful match the value is destructured according to the pattern and the subvalues are bound to the names _key and value (the leading underscore in _key indicating that the contents bound to the name _key will not be used any further).