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Petals

A petal is a Bloom application module compiled to WebAssembly. A deployed petal is content-addressed by its wasm hash and bound to a human-readable path such as /bloom/core/fungible or /bloom/dex/pool.

Petals are invoked through programmable transaction blocks, or PTBs. A PTB can call multiple petal functions, pass outputs from one command into later commands, transfer objects, split and merge coins, and commit or revert atomically.

What Petal Authors Write

Petal authors should start in their own Rust project, not inside the Bloom monorepo. Today, depend on the Bloom repo by git URL, build your crate to wasm, and use the Bloom CLI to deploy the resulting .wasm.

Petal authors write Rust crates that depend on the Bloom runtime and macros:

  • bloom-resource: guest-side runtime types such as Resource<T>, Coin<T>, Capability<T>, Signer, UID, and host wrappers.
  • bloom-resource-macros: #[bloom::petal], #[bloom::object], #[bloom::capability], and #[bloom::invariant].
  • bloom-objects: object IDs, owners, access modes, and type tags.

Every public function inside a #[bloom::petal] module becomes a callable entry point. The macro emits:

  • one wasm export named __petal_<function>;
  • a bloom_petal_manifest_v0 custom section;
  • an accessor for the encoded manifest bytes, used heavily by tests.

What The Chain Uses

At deploy time, Bloom checks that the wasm contains a manifest section, that the manifest path matches the deploy path, and that every manifest function has a matching wasm export.

At call time, the PTB validator loads the manifest, checks argument kinds and object access modes, then the executor runs the wasm under a deterministic chain VM.