Today, if you want to pipe an append or a prepend, you must use then/2 to
achieve this. This can be useful if the first elements of a list must be
inserted in order through a pipe. Let me show an example:
dto.ledger.accounts
|> Enum.reject(fn %{account_number: acc_number} ->
acc_number in [debit_acc_number, credit_acc_number]
end)
|> then(fn accounts -> [get_ordered_debit_accounts() | accounts])
|> then(fn accounts -> [get_ordered_credit_accounts() | accounts] end)
|> then(fn accounts -> accounts ++ retrieve_unordered_accounts() end)
|> then(&Map.replace(dto.ledger, :accounts, &1))
Obviously, that one is too simple and can be done in one line without
losing too much readability, like this:
dto.ledger.accounts
|> Enum.reject(fn %{account_number: acc_number} ->
acc_number in [debit_acc_number, credit_acc_number]
end)
|> then(fn accounts -> [get_ordered_debit_accounts(),
get_ordered_credit_accounts() | accounts])
|> Kernel.++(retrieve_unordered_accounts())
|> then(&Map.replace(dto.ledger, :accounts, &1))
But it could be cleaner if it could just do this:
dto.ledger.accounts
|> Enum.reject(fn %{account_number: acc_number} ->
acc_number in [debit_acc_number, credit_acc_number]
end)
|> List.prepend(get_ordered_debit_accounts())
|> List.prepend(get_ordered_credit_accounts())
|> List.append(retrieve_unordered_accounts())
|> then(&Map.replace(dto.ledger, :accounts, &1))
So I think that the implementation of this can just perform a "remap" of
the ++ operator and the [e | list] expression.
def append(list, element) when is_list(list), do: list ++ [element]
def prepend(list, element) when is_list(list), do: [element | list]
This feature is more of a syntactic sugar than something innovative; it
would be a way to keep the code more vertical and easier to read for some.
*I will be glad to send a PR.*
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