Recursion

Named formats may refer to themselves directly or through other definitions:

list_kind = enum {
    Nil = 0,
    Cons = 1,
}

list = {
    @kind: list_kind,
    value: choose(@kind) {
        Nil => Nothing,
        Cons => {
            head: u8,
            tail: list,
        },
    },
}

The compiler finds strongly connected components (SCCs), so mutually recursive definitions are supported too. It emits owned Box links where Rust needs indirection in the value type.

Parsing. Recurses as the input demands, up to a fixed depth bound statically picked by the format. Exceeding the bound is a parse error.

Preparation and serialization. Preparation walks the value to the same bound, summing lengths, and fails if the value nests deeper than the format allows. Serialization traverses the value and writes the bytes in order.

Note

Though vest_lib defines a bounded fixpoint format combinator that can express arbitrary recursion, the compilation of recursive formats in Vest DSL is experimental: the implementation is incomplete and there is some engineering work remaining for a more robust support.