JSON Adapter

Orchestrations are full of small data plumbing — merge these step outputs, pick that branch — and reaching for an LLM or custom code for it is waste. The JSON adapter covers the plumbing with four pure data manipulation primitives for composing structured outputs and declarative branching. All operations are pure functions with sub-millisecond execution — no IO, no external calls, no tokens spent.

Operations

json:merge — Deep Merge

Merges an array of maps using RFC 7396 JSON Merge Patch semantics. Later values win on key conflict; nested maps merge recursively; null values delete keys.

{
  "operation": "v/ops/json/merge",
  "input": {
    "values": [
      { "decision": "ESCALATED", "tier": "manager" },
      { "invoice": { "vendor": "Acme Corp", "amount": 15600 } },
      { "policy_passed": true }
    ]
  }
}

Result:

{
  "decision": "ESCALATED",
  "tier": "manager",
  "invoice": { "vendor": "Acme Corp", "amount": 15600 },
  "policy_passed": true
}

Use merge to compose outputs from multiple pipeline steps (e.g., LLM decision + invoice data + policy rules).

json:cond — Conditional Selection

Returns the then value of the first case whose when is truthy. Only null and false are falsy — everything else (including 0, "", [], {}) is truthy.

{
  "operation": "v/ops/json/cond",
  "input": {
    "cases": [
      { "when": false, "then": { "route": "auto-approve" } },
      { "when": true,  "then": { "route": "manager", "approver": "J. Martinez" } },
      { "when": false, "then": { "route": "vp" } }
    ],
    "default": { "route": "unknown" }
  }
}

Result: { "route": "manager", "approver": "J. Martinez" }

Use cond for declarative branching in orchestrations without invoking an LLM.

json:assoc — Set Value at Path

Sets a value at a path in a map, creating intermediate maps for missing keys. Equivalent to Clojure assoc-in or Lodash _.set.

{
  "operation": "v/ops/json/assoc",
  "input": {
    "target": { "user": { "name": "alice" } },
    "path": ["user", "email"],
    "value": "alice@example.com"
  }
}

Result: { "user": { "name": "alice", "email": "alice@example.com" } }

The path can be a single string (top-level key) or an array of strings (nested path). Missing intermediate maps are created automatically.

json:select — Pick by Discriminator

Looks up a value in a map of cases by a discriminator key. Like a switch statement.

{
  "operation": "v/ops/json/select",
  "input": {
    "key": "manager",
    "cases": {
      "auto": { "decision": "APPROVED" },
      "manager": { "decision": "ESCALATED", "target": "J. Martinez" },
      "vp": { "decision": "ESCALATED", "target": "VP Finance" }
    }
  }
}

Result: { "decision": "ESCALATED", "target": "J. Martinez" }

Returns default if the key is not found, or null if no default is provided.

Operations Reference

Operation	Input	Description
json:merge	values (array of maps)	RFC 7396 deep merge
json:cond	cases (array of {when, then}), default?	First truthy case
json:assoc	target?, path, value	Set value at nested path
json:select	key, cases (map), default?	Switch on discriminator

Use Cases

• Pipeline composition — merge combines outputs from multiple steps into a single result
• Declarative routing — cond and select branch without LLM calls, keeping orchestrations fast and deterministic
• Data enrichment — assoc adds fields to records before passing them downstream

Related

• Orchestrator — workflow coordination using these primitives
• Agents — agents can call JSON operations as tools