Module eval 

Evaluating a comprehension’s where predicate against a tuple.

A CompiledPredicate parses the predicate once (parse_predicate) and tests each tuple against the tree. ||, &&, !, the comparisons, and membership evaluate directly over the tuple’s values. && and || evaluate their operands left to right and stop at the first that decides the result, so filters folded into one conjunction (R6) evaluate exactly what the chain did; ! negates its operand’s truth. A {name} the tuple does not bind resolves in the scope the tuple was drawn in. Any other expression (arithmetic, a function call, a cast) is interpolated against the tuple over that scope and evaluated as a Polydat expression, charged to the scope’s ledger.

Values compare as scalars: integers and floats compare numerically with each other, strings and booleans with their own kind, and a value of one kind is never equal to a value of another, so "s0" != 2 holds. Ordering values of different kinds is an error. A string is quoted; a bare word is a name, and a predicate has no names beside its elements. A predicate that does not parse is evaluated whole as a Polydat expression. The value a predicate yields is true when it is true or a non-zero number.

None propagates (none_semantics.md Rule 1, comprehension_forms.md §10.9.1). An element the tuple binds to None, and a name that neither the tuple nor the scope binds, reads None, and so does a bare word. A comparison, a membership test, a negation, and an expression that reads None are None; && and || stop at an operand that is None, and are None. A predicate whose value is None keeps no tuple.

Structs

CompiledPredicate

A predicate parsed once, testing tuples.

Enums

ValueKind

The kind every value of an element has, as its source declares it.

Functions

element_kind

The kind of every value name takes in c: the kind its clause’s source declares, the same in every branch of a union, or None when a source’s values are of unknown or mixed kind or c does not bind name.