Expressions

Expressions are how you pass data between resources, validate inputs, and run conditional logic. They are powered by expr-lang.

Where expressions are used

String interpolation -- embed an expression inside any string field using {{ }}:

# resources/example.yaml
chat:
  prompt: "Hello {{ get('name') }}, today is {{ info('timestamp') }}"

before:/after: blocks -- a list of statements executed sequentially. Each statement is a bare expression, not wrapped in {{ }}:

# resources/example.yaml
after:
  - set('normalized', lower(trim(get('q'))))   # stores a value
  - set('is_admin', get('role') == 'admin')    # boolean
  - set('total', get('price') * get('quantity'))

validations.skip / validations.check / onError.when -- a list of boolean expressions; any one true is enough:

# resources/example.yaml
validations:
  skip:
    - get('q') == ''           # bare expression, evaluated as bool
  check:
    - len(get('password')) >= 8

Standard library

Expressions have access to the full expr-lang standard library:

• String: trim(), lower(), upper(), split(), replace(), join()
• Math: min(), max(), abs(), ceil(), floor()
• List: len(), filter(), map(), first(), last()
• String matching (infix operators): contains, startsWith, endsWith, matches
• Type casting: int(), float(), string()

kdeps adds workflow-specific helpers on top. See the Expression Functions Reference for the full list.

See Also

• Expression Functions Reference - All kdeps-specific functions
• Expression Operators - Comparison and logic operators
• Expression Blocks - before: / after: statement blocks