Parse one real line

Trim input, split once, normalize the level, and return a tagged result.

01 · Start with the whole example

Run this first

Run it once, change one input, and compare the new result.

Elixir

# Parse without letting outside text leak inward
parse = fn line ->
  case String.split(String.trim(line), ~r/\s+/, parts: 2) do
    [""] -> :skip
    [level, message] when level in ["INFO", "WARN"] -> {:ok, {String.to_atom(String.downcase(level)), message}}
    _ -> {:error, :invalid_line}
  end
end

{parse.(" INFO ready "), parse.(""), parse.("BROKEN")}

Check the result first

The three results are {:ok, {:info, "ready"}}, :skip, and {:error, :invalid_line}.

02 · Take the code apart

Read from the first line down

Read String.split(..., parts: 2): Split only the level from the remaining message.
Read String.downcase/1: Normalize the level text.
Read {:error, reason}: Return malformed input as data.

03 · Meet the new symbols

Symbols are not secret signs

String.split(..., parts: 2)

Split only the level from the remaining message.

String.downcase/1

Normalize the level text.

{:error, reason}

Return malformed input as data.

04 · Ideas inside the code

Match each name to its meaning

parser boundary

A parser turns outside text into a small internal data shape.

normalization

Normalization converts equivalent spellings to one internal value.

total result

Every input returns one documented result instead of falling through.

05 · Make the idea clear

Why these forms are useful

Run the example first. Predict one result, then change one input and run it again.

A parser turns outside text into a small internal data shape.

Normalization converts equivalent spellings to one internal value.

06 · Change it yourself

Close the answer and try

Accept ERROR disk as an error-level record.

Practice starting point

when level in ["INFO", "WARN", ____]

Target result: Add "ERROR".

Stuck? Read one hint

Keep external levels as strings in the guard.

After you run it, see one answer

One answer

when level in ["INFO", "WARN", "ERROR"]

Think about it: Why split with `parts: 2`?

The message may contain spaces; only the first boundary belongs to the level.

Take with you

Remember these three lines

1
Normalize at the boundary.
2
Return tagged failures.
3
Do not create atoms from unlimited outside text.

Lesson completeRun the code once, then mark this lesson as done.