format: specify two-sorted (integer/bytes) expression evaluation - #286
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gnidan wants to merge 2 commits into
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format: specify two-sorted (integer/bytes) expression evaluation#286gnidan wants to merge 2 commits into
gnidan wants to merge 2 commits into
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DRAFT for writer prose pass before the PR opens. Codifies the two-sorted semantics of pointer expressions: values are either unbounded non-negative integers (no width) or bytes (with a definite width). Arithmetic, JSON-number and odd-nibble-hex literals, $wordsize, and lookups are integers; even-nibble hex, $read, and $sizedN/$wordsized are bytes. An integer is accepted wherever an integer is expected (a bytes value is read as its big-endian integer value), but $concat and $keccak256 operands must be width-bearing bytes — a bare integer there is an error and must be resized first. Fixes the keccak256 example's bare-integer operand to be word-sized, matching what the mapping/string pointer examples already do.
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Pointer expressions had an unstated gap: the width of a value was undefined for numeric literals, arithmetic results, and odd-digit hex, yet
$concatand$keccak256depend on operand widths — so a compiler and a debugger could legitimately disagree on the bytes produced. This specifies the evaluation model.Expressions evaluate to a value of one of two sorts:
The forms are sorted accordingly. Integers: a JSON-number literal,
$wordsize, a variable or lookup, arithmetic ($sum/$difference/$product/$quotient/$remainder), and an odd-digit hex literal (which has no whole-byte width). Bytes: an even-digit hex literal (width = bytes written),$read(width = region length), and$sizedN/$wordsized(width =N/ word size).Coercion runs one way. Where an integer is expected — arithmetic operands, a list
count, a segmentslot/offset/length— a bytes value is read as the non-negative integer its bytes encode (big-endian). Where bytes are expected — the operands of$concatand$keccak256, whose results depend on operand widths — the operand must be width-bearing; a bare integer there is an error and must be given a width with$sizedN/$wordsizedfirst. The resize forms are the only bridge from an integer to bytes; there is no implicit widening.This codifies what the mapping/string pointer examples already do (they word-size a key and slot before hashing). The
keccak256example's bare-integer operand is corrected to$wordsized: 0to match.Note: this is the core semantics for a future extraction of the expression language into a shared facility — the integer/bytes sorting discipline is meant to carry over. The
@ethdebug/pointersevaluateimplementation currently uses a single width-carrying representation and does not yet enforce the width-bearing rule; that is a tracked follow-up on the pointers side, not part of this spec change.Schema example and validity tests pass.