#Advanced Topics

The Medaka Guide gets you writing programs. The chapters here go deeper into one part of the language at a time, for readers who have finished the guide and want to know how a feature actually works, what it can express, and where its edges are.

Each topic is a short sequence of chapters that starts from what the guide already taught and builds up from there. Read a topic in order the first time; the later chapters assume the earlier ones.

Every example that can run does run. As in the guide, a ```medaka block is compiled by the test suite before a change can merge, and a block with output shown beneath it is executed and the output compared. Where a chapter shows what medaka check prints for a program, or quotes an error message, that text was pasted from the compiler, not paraphrased.

#Topics

Effects. How the effect row in a signature is inferred and checked, how effects flow through higher-order functions, how to declare labels of your own, how a label can carry a parameter that says which file, host, or variable a function may touch, how that authority moves through data, and how the whole thing turns into a capability manifest a host can read.

1. What the Row Says. Latent and immediate effects, inference, the escape check, the built-in labels, and the rows of values.
2. Effect Polymorphism. Effect variables, open rows, callbacks, composition, interfaces, and callbacks stored in data.
3. Labels, Manifests, and the Host. Declaring labels, medaka manifest and check-policy, main as the grant root, and FFI.
4. Parameters and Authority. Prefix, Set, and Product domains, named arguments, how the compiler reads a path, and qualified values.
5. Authority in Data. Authority-indexed types, constructors as proof, invariance, existentials, and what may be exported.
6. Effect-Indexed Types. Types that store a computation and record its row in an index.
7. Reference and Open Edges. Every spelling on one page, the diagnostics, and the known gaps.