generateUntilValid

Generate → validate → retry loop. If the generated output fails validation the error message is placed on shared state so the generator can correct itself on the next attempt.

Distinct from the withStructuredOutput plugin (which wraps every step) — this is a self-contained flow for a single generation step with retry logic.

Import

import { generateUntilValid } from "flowneer/presets/pipeline";

Usage

interface CodeState {
  prompt: string;
  code: string;
  __validationError?: string;
}

const flow = generateUntilValid<CodeState>({
  generate: async (s) => {
    const hint = s.__validationError
      ? `\nPrevious error: ${s.__validationError}`
      : "";
    s.code = await llm(`Write a TypeScript function.${hint}\n${s.prompt}`);
  },
  validate: (s) => {
    try {
      new Function(s.code);
      return true;
    } catch (e) {
      return (e as Error).message;
    }
  },
  maxAttempts: 3,
});

await flow.run({ prompt: "Sort an array of numbers", code: "" });

Options

Option	Type	Default	Description
generate	NodeFn<S, P>	—	Produces the output. On retries (shared as any).__validationError holds the previous error message
validate	(shared, params) => true | string | Promise<true | string>	—	Return true when valid, or an error string to retry
maxAttempts	number	3	Maximum generation attempts

State keys

Key	Description
__validationError	undefined on success, or the last validation error string if all attempts failed

Return value

Returns a FlowBuilder<S, P>:

const flow = generateUntilValid({ generate, validate })
  .withTiming()
  .withCostTracker();

See Also

• mapReduceLlm — batch LLM calls across N items
• withStructuredOutput — step-level output parsing and retry