Module expr 

Recursive-descent parser for WHERE-clause filter expressions.

Converts a human-readable query string like city = "Accra" AND age >= 25 into an Expr AST that the document engine evaluates against packed documents or uses for index lookups.

Grammar

expr       = or_expr
or_expr    = and_expr ( "OR" and_expr )*
and_expr   = primary  ( "AND" primary )*
primary    = "NOT" primary
           | "(" expr ")"
           | IDENT "EXISTS"
           | IDENT "IN" "(" value ("," value)* ")"
           | IDENT op value
op         = "=" | "!=" | ">" | ">=" | "<" | "<=" | "CONTAINS"
value      = STRING | NUMBER | "true" | "false" | "null"

AND binds tighter than OR, matching SQL precedence. Keywords (AND, OR, NOT, IN, EXISTS, CONTAINS, TRUE, FALSE, NULL) are case-insensitive. Field names may contain dots to address nested paths (e.g., address.city).

Lexer

A single-pass byte-oriented [Lexer] tokenises the input into identifiers, string literals (single- or double-quoted), numeric literals (including negatives and decimals), operators, and keywords.

Parser

A top-down [Parser] consumes the token stream using the precedence climbing pattern: parse_or calls parse_and, which calls parse_primary, yielding left-associative trees for chained conjunctions and disjunctions.

Enums

Expr

Parsed WHERE clause expression AST.

ExprError

Errors that can occur while parsing a WHERE expression.

ExprValue

A literal value in a WHERE expression.

Functions

parse_where

Parse a WHERE clause string into an Expr AST.