Control Flow

WCL provides two declarative control flow structures: for loops and if/else conditionals. Unlike imperative languages, these constructs do not execute at runtime — they expand into concrete blocks and attributes during the control flow expansion phase of the pipeline, before evaluation.

This design keeps WCL configs purely declarative: the final evaluated document contains no loops or conditionals, only the concrete values they produced.

Structures

• For Loops — iterate over lists, ranges, or query results to generate repeated blocks or values.
• If/Else Conditionals — conditionally include blocks, attributes, or children based on boolean expressions.

Expansion Phase

Both constructs are processed during phase 5: control flow expansion, after macro expansion and before partial merge and evaluation. At the end of this phase, the AST contains only concrete nodes.

Limits

To prevent runaway configs and protect tooling performance, WCL enforces the following hard limits:

Exceeding any of these limits is a compile-time error. The limits exist to keep configs analyzable and prevent accidental exponential expansion.

Composition

For loops and if/else can be freely composed:

for env in ["staging", "prod"] {
  service web-${env} {
    replicas: if env == "prod" { 3 } else { 1 }
  }
}

See the individual pages for full syntax, scoping rules, and examples.