Control Flow Examples

This example demonstrates control flow in kdeps:

• if-else via ternary operator (? :)
• and/or via logical operators (&&, ||, !)
• while loops via the loop resource block (Turing-complete)
• list operations via functional expressions (filter, map, all, any)

Conditional Iteration: loop

The loop block enables unbounded while-loop iteration in a resource:

run:
  loop:
    while: "loop.index() < 5"
    maxIterations: 1000   # safety cap (default: 1000)
  expr:
    - "{{ set('result', loop.count()) }}"
  apiResponse:
    success: true
    response:
      count: "{{ get('result') }}"

• loop.index() — current iteration index (0-based)
• loop.count() — current iteration count (1-based)
• loop.results() — results from all prior iterations (for self-referential termination)
• set('key', val, 'loop') / get('key', 'loop') — loop-scoped storage

Multiple iterations with apiResponse produce a streaming response (a slice of per-iteration maps).

Features Demonstrated

1. If-Else (Ternary Operator)

# Simple condition
status: {{age >= 18 ? "adult" : "child"}}

# Nested conditions  
category: {{age < 13 ? "child" : (age < 20 ? "teen" : "adult")}}

# With calculations
discount: {{premium ? price * 0.8 : price}}

2. Logical Operators

# AND
eligible: {{age >= 18 && verified}}

# OR
hasAccess: {{premium || trial}}

# NOT
enabled: {{!disabled}}

# Complex
canPurchase: {{(age >= 18 && verified) || admin}}

3. While Loop

# Count to N
loop:
  while: "loop.index() < 10"
  maxIterations: 100

# Accumulate until threshold
loop:
  while: "int(default(get('sum'), 0)) <= 20"
  maxIterations: 100

# Collect N results
loop:
  while: "len(loop.results()) < 3"
  maxIterations: 10

4. List Operations

# Filter (like: for item in items if condition)
adults: {{filter(users, .age >= 18)}}

# Map (like: [item.name for item in items])
names: {{map(users, .name)}}

# All (like: all(item.valid for item in items))
allValid: {{all(items, .valid)}}

# Any (like: any(item.active for item in items))
hasActive: {{any(items, .active)}}

Running the Example

kdeps run examples/control-flow/workflow.yaml

Learn More

• Loop Iteration Documentation - Complete loop guide
• Control Flow Documentation - Expressions and conditionals
• expr-lang Documentation - Full language reference