Expression Functions Reference

Every function available in kdeps expressions -- usable in any field that supports {{ }} interpolation or in expr blocks.

Core Functions

The four functions used in almost every resource: read data, write data, access uploaded files, and read request metadata.

get(key, typeHint?)

Retrieves data from any source.

• key: The key to look up.
• typeHint (optional): Force a specific source (param, header, session, memory, item, env, file, filepath, filetype).

Examples:

get('q')                     # Auto-detect source
get('Authorization', 'header') # Get from headers
get('user_id', 'session')    # Get from session
get('API_KEY', 'env')        # Get environment variable

set(key, value, storage?)

Stores data in memory or session.

• key: The key to store.
• value: The value to store.
• storage (optional): Storage type (memory or session). Default is memory.

Examples:

set('count', 1)              # Store in memory (request-scoped)
set('user', data, 'session') # Store in session (persistent)

file(pattern, selector?)

Accesses uploaded files or local files.

• pattern: Glob pattern or file name.
• selector (optional): first, last, count, all, mime:<type>.

Examples:

file('*.jpg')                # Get all JPG files content
file('*.pdf', 'first')       # Get content of first PDF
file('*', 'count')           # Get total file count

info(field)

Retrieves request metadata.

• field: One of ID, IP, timestamp, path, method, sessionId, filecount, files, filetypes.

Examples:

info('ID')                   # Get request ID
info('IP')                   # Get client IP

Data Handling Functions

Utilities for converting, inspecting, and safely traversing data structures.

json(data)

Converts data to a JSON string.

• data: The data to stringify.

Examples:

json(get('userData'))        # Convert object to JSON string

safe(obj, path)

Safely accesses nested properties without panicking on nil values.

• obj: The object to access.
• path: Dot-notation path to the property.

Examples:

safe(user, "profile.address.city") # Returns city or nil if path invalid

debug(obj)

Returns a pretty-printed JSON string representation of an object for debugging.

• obj: The object to inspect.

Examples:

debug(get('httpResponse'))   # Inspect complex object structure

default(value, fallback)

Returns a fallback value if the primary value is nil or empty.

• value: The value to check.
• fallback: The value to return if primary is nil/empty.

Examples:

default(get('limit'), 10)    # Return 10 if limit is missing

Input/Output Functions

Explicit accessors for request inputs and resource outputs -- use these when get() auto-detection is ambiguous.

input(name, type?)

Accesses input data (similar to get but strictly for inputs).

• name: Input name.
• type (optional): param, header, body.

Examples:

input('q')                   # Get query param
input('body')                # Get request body

output(resourceId)

Accesses the output of a completed resource.

• resourceId: The actionId of the resource.

Examples:

output('llmResource')        # Get LLM output

Iteration Functions

Available inside items: blocks to access the state of the current loop iteration.

item object

Accesses current iteration context. item is an object -- call its methods to read iteration state.

Methods:

item.current()   # Current item value
item.prev()      # Previous item (nil on first iteration)
item.next()      # Next item (nil on last iteration)
item.index()     # Current index (0-based)
item.count()     # Total items count
item.values()    # All items as an array

Session Functions

Access session-scoped data set with set('key', val, 'session') in any resource.

session()

Returns the entire session data object.

Examples:

session()                    # Get all session data

Array Operations

filter(array, predicate)

Filters an array by a predicate expression. Use . to reference the current element.

# resources/example.yaml
after:
  - set('activeUsers', filter(get('users'), .status == 'active'))
  - set('premiumActive', filter(get('users'), .status == 'active' && .tier == 'premium'))
  - set('expensiveItems', filter(get('products'), .price > 100))

map(array, expression)

Transforms each element in an array.

# resources/example.yaml
after:
  - set('userNames', map(get('users'), .name))
  - set('emails', map(get('users'), .email))
  - set('pricesWithTax', map(get('items'), .price * 1.1))

Aggregation

# resources/example.yaml
after:
  - set('total', sum(get('prices')))
  - set('minPrice', min(get('prices')))
  - set('maxPrice', max(get('prices')))
  - set('avgPrice', sum(get('prices')) / len(get('prices')))

slice(array, start, end)

Extracts a sub-array. Negative indices count from the end.

# resources/example.yaml
after:
  - set('firstFive', slice(get('items'), 0, 5))
  - set('lastTen', slice(get('items'), -10, len(get('items'))))

first(array) / last(array)

Returns the first or last element of an array.

# resources/example.yaml
after:
  - set('firstItem', first(get('items')))
  - set('lastItem', last(get('items')))

len(value)

Returns the length of an array or string.

# resources/example.yaml
after:
  - set('itemCount', len(get('items')))
  - set('textLength', len(get('text')))

String Operations

Case Conversion

# resources/example.yaml
after:
  - set('lowercase', lower(get('text')))
  - set('uppercase', upper(get('text')))
  - set('trimmed', trim(get('text')))

Splitting & Joining

# resources/example.yaml
after:
  - set('words', split(get('csv'), ','))
  - set('lines', split(get('text'), '\n'))
  - set('commaSeparated', join(get('items'), ', '))

Replacing

# resources/example.yaml
after:
  - set('replaced', replace(get('text'), 'old', 'new'))

String Matching

contains, startsWith, endsWith, and matches are infix operators, not functions.

# resources/example.yaml
after:
  - set('hasKeyword', get('text') contains 'important')
  - set('isUrl', get('url') startsWith 'https://')
  - set('isImage', get('filename') endsWith '.jpg')
  - set('isEmail', get('email') matches '^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\\.[a-zA-Z]{2,}$')

Type Conversion

type(value)

Returns the type as a string: "string", "int", "float", "bool", "array", "map", "nil".

# resources/example.yaml
after:
  - set('valueType', type(get('value')))

Casting Functions

# resources/example.yaml
after:
  - set('age', int(get('ageString')))       # "123" -> 123
  - set('price', float(get('priceString'))) # "3.14" -> 3.14
  - set('idString', string(get('id')))      # 42 -> "42"

Date & Time

info('timestamp')

Returns the current time as an RFC3339 string (e.g. 2024-12-25T14:30:00Z). Use this for timestamps in responses, logging, and audit fields.

# resources/example.yaml
after:
  - set('ts', info('timestamp'))

now()

Returns the current time as a time.Time value. Useful with comparison operators or passing to date() for parsing.

# resources/example.yaml
after:
  - set('currentTime', now())

Conditional Logic

Ternary Operator

# resources/example.yaml
after:
  - set('status', get('score') >= 70 ? 'pass' : 'fail')
  - set('discount', get('isPremium') ? 0.2 : 0.1)

Null Coalescing

The ?? operator returns the right-hand value when the left-hand is nil or empty string.

# resources/example.yaml
after:
  - set('name', get('name') ?? 'Anonymous')
  - set('limit', get('limit') ?? 10)

Operator Precedence

Expressions evaluate left-to-right with this precedence (highest to lowest):

1. Parentheses: (a + b) * c
2. Unary: !, -
3. Multiplicative: *, /, %
4. Additive: +, -
5. Comparison: <, <=, >, >=
6. Equality: ==, !=
7. Logical AND: &&
8. Logical OR: ||
9. Ternary: ? :
10. Null coalescing: ??

Best Practices

• Use parentheses for clarity -- (a + b) * c is clearer than relying on precedence
• Break complex expressions into multiple statements for readability
• Validate before processing -- check types and null values before operations
• Keep expressions simple -- complex logic belongs in Python resources

See Also

• Expressions Guide -- where expressions are used and basic syntax
• Validation & Control Flow -- skip, check, and error handling
• Inline Resource Blocks -- before: and after: expression blocks