Attribute Macro chain 

#[chain]

Convert an async function into a BoxRunnable<InputType, OutputType> factory.

The macro generates a public function with the same name that returns a BoxRunnable backed by a RunnableLambda.

The output type is inferred from the function signature:

• Result<Value, _> → BoxRunnable<I, Value> (serializes to Value)
• Result<String, _> → BoxRunnable<I, String> (direct return)
• Result<T, _> → BoxRunnable<I, T> (direct return)

Example

use synaptic_macros::chain;
use synaptic_core::SynapticError;
use serde_json::Value;

#[chain]
async fn uppercase(input: Value) -> Result<Value, SynapticError> {
    let s = input.as_str().unwrap_or_default().to_uppercase();
    Ok(Value::String(s))
}

// Returns BoxRunnable<Value, Value>
let runnable = uppercase();

// Typed output — returns BoxRunnable<String, String>
#[chain]
async fn to_upper(s: String) -> Result<String, SynapticError> {
    Ok(s.to_uppercase())
}