dagql/dirty

// 1. make an app
const app = mvfm(prelude, console_);

// 2. make a program: x + 10
const prog = app({ x: "number" }, ($) =>
  $.begin($.console.log("result:", $.add($.input.x, 10)), $.add($.input.x, 10))
);

const injected = injectInput(prog, { x: 5 });

// 3. dagql: dirty opens the NExpr for mutation
const d = dirty(injected.__nexpr);

// swapEntry replaces a single node by ID
const ids = selectWhere(injected.__nexpr, byKind("num/add"));
const addId = [...ids][0];
const entry = d.__adj[addId];
const swapped = swapEntry(d, addId, {
  ...entry,
  kind: "num/sub",
});

// commit seals it back to an immutable NExpr
const result = commit(swapped);

// 4. fold: was 5+10=15, now 5-10=-5
await fold(result, defaults(app));