# CodeUChain (Python) – Cheat Sheet

Full reference: `docs/python/llm-full.txt`

## Quick Start
```bash
pip install codeuchain
```
```python
from codeuchain import State, Chain
ctx = State({"payload": "hi"})
res = await chain.call(ctx)
```

## Primitives
- Link: async `call(ctx: State[TIn]) -> State[TOut]`
- State: immutable mapping; `insert`, `insert_as`
- Chain: composition + `.catch()`
- Hook: `before/after/error` coroutines

## Minimal Link
```python
class Parse(Link[Any, Any]):
        async def call(self, ctx: State[Any]) -> State[Any]:
                return ctx.insert("parsed", True)
```

## Chain Example
```python
chain = Chain() \
    .then(Validate()) \
    .then(Parse()) \
    .catch(lambda name, err, ctx: ctx.insert("error", str(err)))
```

## Type Evolution
```python
c2: State[Parsed] = c1.insert_as("parsed", Parsed(tokens=toks))
```

## Error Classification
Retry transient (I/O, timeout). Surface validation/security.

## Performance Tips
- Reuse event loop tasks
- Avoid deep copy of large dict entries
- Log structured keys only

## ASCII Pipeline
```
[In] -> (Validate) -> (Parse) -> (Enrich) -> [Out]
```

## TL;DR
Async links + immutable/evolving states + graceful hook.

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