playground

name	playground
description	Quick code experimentation using IEx tool

Playground Skill

Use the iex tool for quick experimentation and debugging Elixir code.

Why use IEx tool?

The IEx tool provides a persistent Elixir session where you can:

• Test functions without writing files
• Experiment with data transformations
• Debug complex expressions
• Validate code before implementing it

Each session maintains state across tool calls, so variables persist.

Usage patterns

Test a function

iex("MyModule.my_function(arg1, arg2)")

Inspect data structures

iex("data = %{key: \"value\", nested: %{a: 1}}")
iex("Map.keys(data)")  # Variables persist across calls

Debug with IO.inspect

iex("[1, 2, 3] |> Enum.map(&(&1 * 2)) |> IO.inspect(label: \"doubled\")")

Test pipes

iex("""
[1, 2, 3, 4, 5]
|> Enum.filter(&rem(&1, 2) == 0)
|> Enum.map(&(&1 * 2))
|> Enum.sum()
""")

Validate regex

iex("Regex.match?(~r/[0-9]+/, \"abc123\")")

Check module functions

iex("MyModule.__info__(:functions)")

Common Elixir patterns to test

Pattern matching

iex("{:ok, value} = {:ok, 42}")
iex("value")  # => 42

List operations

iex("list = [1, 2, 3]")
iex("[head | tail] = list")
iex("head")  # => 1
iex("tail")  # => [2, 3]

Map operations

iex("map = %{a: 1, b: 2}")
iex("Map.put(map, :c, 3)")
iex("Map.get(map, :a)")
iex("map.a")  # Access syntax

Enum operations

iex("Enum.reduce([1, 2, 3], 0, &+/2)")
iex("Enum.zip([1, 2], [:a, :b])")
iex("Enum.group_by([\"apple\", \"apricot\", \"banana\"], &String.first/1)")

String operations

iex("String.split(\"hello world\", \" \")")
iex("String.upcase(\"hello\")")
iex("\"hello #{\"world\"}\"")  # String interpolation

Debugging techniques

Inspect intermediate steps

iex("""
[1, 2, 3, 4]
|> IO.inspect(label: "original")
|> Enum.map(&(&1 * 2))
|> IO.inspect(label: "doubled")
|> Enum.sum()
|> IO.inspect(label: "sum")
""")

Check type

iex("is_binary(\"hello\")")
iex("is_atom(:hello)")
iex("is_list([1, 2, 3])")

Timing operations

iex(":timer.tc(fn -> Enum.reduce(1..10000, 0, &+/2) end)")

When to use IEx tool

✅ Good use cases:

• Testing a function before writing it to a file
• Validating regex patterns
• Exploring data structures
• Quick calculations
• Checking if a module/function exists

❌ Don't use for:

• Long-running operations (use shell tool instead)
• File I/O (use read_file/write_file tools)
• Installing dependencies (use shell + mix commands)

Best practices

1. Keep it simple: IEx is for quick tests, not full programs
2. Use multiline strings for complex expressions (triple quotes """)
3. Variables persist: You can build up state across multiple iex calls
4. Check errors first: If uncertain about syntax, test in IEx before editing files

Example workflow

# User asks: "How do I get unique values from a list?"

# Test it in IEx first
iex("Enum.uniq([1, 2, 2, 3, 3, 3])")
# => [1, 2, 3]

# Verify it works with strings
iex("Enum.uniq([\"apple\", \"banana\", \"apple\"])")
# => ["apple", "banana"]

# Then implement it in actual code
write_file(
  path: "lib/helper.ex",
  content: """
  defmodule Helper do
    def unique_values(list) do
      Enum.uniq(list)
    end
  end
  """
)