And we can do something crazy (for practicing tail recursion, of course. You don’t wanna use this sorta code in production).
The following code assumes there’s no mismatching bracket, and there’s no nested bracket. The code is NOT unicode-safe.
defmodule MyTemplate do
@spec consolidate(String.t, %{optional(String.t) => String.t}) :: String.t
def consolidate(template, replacements) do
do_consolidate(template, replacements, [], nil)
end
# I know @doc has no effect on private functions,
# but it looks better to write docs in this way.
@doc """
Handle the consolidation progress one character at a time.
## Params
- `template`: the yet-to-handle part of the template string.
- `replacements`: the map of replacements.
- `acc`: an IO list. The accumulator of the content generated so far.
- `placeholder`: `nil` or an IO list.
If `placeholder` is `nil`, it means this function is handling a character out of any brackets,
otherwise, this function is handling a character inside a bracket.
## Return value
A string with all placeholders replaced with their corresponding values in `replacements`.
"""
defp do_consolidate("[" <> rest, replacements, acc, nil) do
# Encountered an open bracket outside any brackets.
# The next few characters should be a placeholder,
# so recurse with an empty IO list to store the placeholder.
do_consolidate(rest, replacements, acc, [])
end
defp do_consolidate("]" <> rest, replacements, acc, placeholder) do
# Encountered a close bracket.
# `placeholder` should contain all the characters of a placeholder,
# so we lookup the value in `replacements` and append it to `acc`.
placeholder = IO.iodata_to_binary(placeholder)
value = replacements[placeholder] || ""
do_consolidate(rest, replacements, [acc, value], nil)
end
defp do_consolidate(<<char::binary-1, rest::binary>>, replacements, acc, nil) do
# Encountered a non-bracket character outside any brackets.
# Just append the character to `acc`.
do_consolidate(rest, replacements, [acc, char], nil)
end
defp do_consolidate(<<char::binary-1, rest::binary>>, replacements, acc, placeholder) do
# Encountered a non-bracket character inside a bracket.
# This character should be part of a placeholder,
# so we append this character to `placeholder`.
do_consolidate(rest, replacements, acc, [placeholder, char])
end
defp do_consolidate("", _replacements, acc, nil) do
# The whole template is handled.
# Just convert `acc` to a string and return it.
IO.iodata_to_binary(acc)
end
end
You can try call it:
template = """
Hi [name],
Thank you for your time in our office.
Thank you for booking at [company] for [time].
Regards
[salesguy]
"""
template
|> MyTemplate.consolidate(%{
"company" => "The Chocolate Factory",
"name" => "Charlie Bucket",
"salesguy" => "Willy Wonka",
"time" => "Aug 12, 2021"
})
|> IO.puts()
