Write a function that transforms a list of names to uppercase.

Use a stream pipeline with map to transform each item:

  uppercased <- cat names
    | map with toUpper
    | collect as List of String

The 'map with' operation applies a function to each item in the stream. The function must take one argument and return one value.

Define the transformation as a named pure function:

  toUpper() as pure
    -> name as String
    <- rtn as String: name.upperCase()

Then use it in the pipeline. This is cleaner than a loop because:
- The intent is clear: transform each item
- The function is testable on its own
- No mutable accumulator needed

For output instead of collecting:

  cat names | map with toUpper > stdout

Example

defines module qa.streams.codertransform

  defines function

    toUpper() as pure
      -> name as String
      <- rtn as String: name.upperCase()

    addGreeting() as pure
      -> name as String
      <- rtn as String: "Hello, " + name

  defines program

    StreamTransformDemo()
      stdout <- Stdout()

      names <- ["alice", "bob", "charlie"]

      //Transform to uppercase
      uppercased <- cat names
        | map with toUpper
        | collect as List of String
      stdout.println(`Uppercased: ${uppercased}`)

      //Chain transformations
      cat names
        | map with toUpper
        | map with addGreeting
        > stdout

Common mistakes

E01010 — EK9 streams use pipe syntax with named functions. Write 'cat source | map with functionName | collect as Type'.

Incorrect:

      uppercased <- names.map(n -> n.upperCase())

Correct:

      uppercased <- cat names
        | map with toUpper
        | collect as List of String

Other ways to ask this

How do I map a list of strings to uppercase in EK9?
Write code to convert all items in a list using a stream
Show me how to use map with in a stream pipeline

Coming from another language?

EK9 uses 'cat source | map with fn | collect as Type' for list transformations. Named functions replace lambdas.

Keywords: map, stream, coder, transform, pipeline, uppercase