Expressions

Expressions allow you to add logic, data transformation, and dynamic values to your workflow. They are powered by the expr-lang engine.

Where to Use Expressions

1. String Interpolation

Use {{ }} to embed expressions in any string field.

run:
  chat:
    prompt: "Hello {{ get('name') }}, today is {{ info('timestamp') }}"

2. Expression Blocks (expr)

Use expr blocks to run logic steps. These are executed sequentially.

run:
  expr:
    # Variable assignment
    - set('normalized_query', lower(trim(get('q'))))
    
    # Conditional logic
    - set('is_admin', get('role') == 'admin')
    
    # Math
    - set('total', get('price') * get('quantity'))

3. Conditions

Used in skipCondition, preflightCheck, and onError.

skipCondition:
  - get('q') == ''

preflightCheck:
  validations:
    - len(get('password')) >= 8

Expression Types

KDeps supports three types of expressions:

Literal

Raw values returned as-is.

key: "value"
count: 10

Direct

Evaluated directly (used in expr blocks and conditions).

- get('count') + 1
- user.name == 'Alice'

Interpolated

String templates containing {{ }}.

message: "Count is {{ get('count') }}"

Standard Library

Since KDeps uses expr-lang, you have access to a rich standard library of functions:

• String: trim(), lower(), upper(), split(), replace(), join()
• Math: min(), max(), abs(), ceil(), floor()
• List: len(), filter(), map(), first(), last(), contains()
• Type: int(), float(), string(), bool()

See the Expr Language Documentation for a full list of built-in operators and functions.

Helper Functions

KDeps adds specific helper functions for workflow context. See the Expression Functions Reference for details.