Struct ClauseYield 

pub struct ClauseYield {
    pub var: String,
    pub source: Option<String>,
    pub evaluations: usize,
    pub values: usize,
}

Internal walker state — the scope the recursive walker resolves names against, so it does not thread it through every call. What one leaf clause yielded over a whole traversal.

A clause under a cartesian is evaluated once per outer tuple, so emptiness is a property of the evaluations and not of the clause:

• evaluations == 0 — never reached, because something outside it was empty first. Not the cause; the cause is an earlier clause.
• evaluations > 0 && values == 0 — reached and yielded nothing every time. This is the clause a diagnostic should name.
• values > 0 — yielded.

An empty stream is a legal value of the algebra, so none of these is an error. What a host does about one is the host’s policy.

Why an evaluation yielded nothing, when the reason is a read of None, is reported beside these records by evaluate_for_iteration_with_none_reads (NoneReads).

Fields

var: String

The clause’s element name.

source: Option<String>

The source’s canonical text, when it has one.

evaluations: usize

How many times this clause was evaluated.

values: usize

How many values it produced, summed over those evaluations.

Trait Implementations

impl Clone for ClauseYield

fn clone(&self) -> Self

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Debug for ClauseYield

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

Formats the value using the given formatter.

impl Eq for ClauseYield

impl PartialEq for ClauseYield

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

Equality operator ==.

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

Inequality operator !=.

impl StructuralPartialEq for ClauseYield