Module arithmetic 

$(( )) — checked 64-bit integer arithmetic and another-base number reading.

Three stages, kept separate so each can be tested on its own: tokenize (text → Tok), parse (Tok → ArithExpr), and evaluation (eval_sync for a scope with no $(...) reachable, and Kernel::eval_arith_async in kernel.rs for the general case).

Supports: decimal/hex/base#digits literals (base 2..=36), the full C precedence table down through ?:, $name/${...}/$(...)/nested $((...)) as operands, and bare (( expr )) as a condition (see Stmt::Arith/Expr::Arith in ast/types.rs).

Diverges from bash on purpose: overflow is an error, never a wrap; a leading-zero numeral is refused, never read as octal; an unset or empty operand is an error, never 0; $(...) on the unselected side of &&/||/?: never runs.

Structs

ArithError

An error from tokenizing, parsing, or evaluating $(( )). message is the full, final text shown to the caller; span is the byte range in the arithmetic source the error concerns, when one exists (evaluation errors over already-resolved values carry 0..0 — the message already names the values).

Functions

eval_arithmetic

Tokenize, parse, and evaluate text (the content of $(( ))) with no $(...) support — the fast path used where an async evaluator isn’t available. A reachable $(...) errors loudly rather than silently resolving to nothing.