Type-checking the everlasting flame at v0.1.1
Tau (τ) is a runtime type-validation library for GraalVM Polyglot values. It was primarily designed for Fuse's needs of seamless type-safe integration with JavaScript. Despite its origins, Tau is a general-purpose library and doesn't rely on Fuse in any way.
You'll surely find the artifacts to depend on here once Tau leaves its beta stage.
Note
Throughout this section, the /.../ circumfix syntax is used to denote Value literals. /42/ thus defines a Value of 42. You will shortly discover that
the /.../ syntax isn't used coincidentally.
Type validation in Tau is done through Templates. A template may be thought of as a reusable, bidirectional type-schema, that is capable of describing itself.
A Template functions as a type-safe mapping from a Value to some type T, and vice versa. The former operation
is referred to as lower, and the latter as raise. Both operations produce an Option which signals
whether the conversion was successful.
Tip
Tau.lower()/Tau.raise() are convenient ways to assert that the respective operation was successful, throwing
an absurdly pretty exception if it wasn't:
Tau.lower(Template.STRING, /"Marie"/);A Template may be composed declaratively from primitives and factory methods found
in the Template class.
Being written specifically for Fuse, Tau was developed with user-facing exceptiosn in mind. Hence,
Tau includes an awfully over-engineered Description system.
A Description is a textual representation of a some type schema. Tau is capable of
inferring a Description from multiple sources, as well as building one from a Template.
The source a Description was inferred from is called a Domain. When inferring a description, Tau annotates it with
the domain it's coming from. The domain is visible in a description as a set of purple brackets.
