Enum Decision 

pub enum Decision<'a> {
    Test {
        scrutinee: Occurrence,
        outcome: Outcome,
        matched: Box<Decision<'a>>,
        default: Box<Decision<'a>>,
    },
    Leaf {
        bindings: Vec<Binding>,
        body: &'a TypedTerm,
    },
    Fail {
        declaration: Name,
    },
}

The tree a case’s branches lower to: what test distinguishes which branch, in what order they are tried, and the names each leaf binds.

'a is the lifetime of the TypedTerm the branches were built from: a leaf borrows its branch’s body rather than cloning it, since TypedTerm carries no Clone impl. A body can appear in more than one leaf once a fallback tree is copied (see this module’s doc comment), which a borrow makes free in the IR; a backend that writes each leaf out writes the body once per leaf (GEN-26).

Two trees are equal when they have the same shape and each pair of leaves borrows the same body — compared by address, since TypedTerm has no PartialEq. That is the equality a test wants: the leaf is the one built from this branch.

Variants

Test

Check the value at scrutinee against outcome: matched if it is that value, default if it is not.

Fields

scrutinee: Occurrence

outcome: Outcome

matched: Box<Decision<'a>>

default: Box<Decision<'a>>

Leaf

A branch matched: its bindings, each already named and given the occurrence to read it from, and its body.

Fields

bindings: Vec<Binding>

body: &'a TypedTerm

Fail

No branch matches.

Coverage is checked, so no such case compiles — but nothing checks it yet (LANG-19), so a case missing a branch compiles today and reaches this leaf at runtime. It is not deleted the day LANG-19 lands: an unreachable leaf still has to abort rather than fall through to whatever follows it, and this is that leaf — merely one exhaustiveness will have made unreachable, rather than one still worth reaching for.

Fields

declaration: Name

The declaration the case was written in: what the description $abort takes (runtime/js/zelkova.mjs, added by GEN-8) is built from.

This is whatever build’s caller passed, not something the tree finds: nothing in a case’s branches says which declaration they sit in, so naming it is the caller’s contract — a backend walking a declaration’s body has that declaration’s name at hand. Neither the $abort call nor the description’s exact wording is this pass’s to write; walking a Decision to build them is zelkova_js::emit’s.

Trait Implementations

impl<'a> Clone for Decision<'a>

fn clone(&self) -> Decision<'a>

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl<'a> Debug for Decision<'a>

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl PartialEq for Decision<'_>

fn eq(&self, other: &Self) -> bool

Equality operator ==.

fn ne(&self, other: &Rhs) -> bool

Inequality operator !=.