3. Conditions and loops

Zryna 0.2.1 at 841c8aee901782c9f7bf442bfe8eb2fe6b7f6446 publishes if, optional else, lexical blocks, and while through control-flow-v1. See the exact M2_CONTROL_FLOW_SEMANTICS.md.

export function sumTo(limit: i32): i32 {
  let next: i32 = 1;
  let total: i32 = 0;
  while (next <= limit) {
    total = total + next;
    next = next + 1;
  }
  return total;
}

export function choose(enabled: bool, yes: i32, no: i32): i32 {
  if (enabled) {
    return yes;
  }
  return no;
}

Every condition must be exactly bool. A while reevaluates its condition on each visit. Every reachable function path must return its declared type.

Run the loop:

& $zryna run src/control.zry `
  --project-root "$workspace\tutorial-control" `
  --profile control-flow-v1 `
  --target webassembly `
  --name sum-to-five `
  --export sumTo `
  --arg=i32:5

Expected output: webassembly: i32 15.

Run the branch with --export choose --arg=bool:false --arg=i32:40 --arg=i32:2; the result is i32 2.

What is not supported

The 0.2.1 control-flow profile does not admit for, break, continue, switch, labels, exceptions, async control flow, recursion, or implicit truthiness. Use the supported while form rather than translating syntax from JavaScript mechanically.

Common errors

• ZRYNA-M2014 means an if or while condition was not exactly bool.
• ZRYNA-M2009 covers missing, wrong, or unreachable returns.
• A loop whose condition never becomes false can hit the bounded execution deadline; it is not treated as proof that the function returns.

Exercise

Predict and then run sumTo(0), sumTo(1), and sumTo(10) on either portable target. Why does zero skip the body?

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