eyeprolog

ISO/IEC 13211-3 (Definite clause grammar rules) — implementation status

This document records what EyeProlog implements of Prolog Part 3, non-terminal by non-terminal and predicate by predicate. It is a status ledger, not a conformance claim.

Normal mode implements the whole grammar surface below. --iso-strict leaves -->/2 as ordinary Part 1 operator syntax and excludes grammar expansion and phrase/2-3 from the strict registry, so phrase/2 there raises existence_error(procedure, phrase/2).

Grammar control constructs (clause 7.14)

Clause	Construct	Status
7.14.1	`[]//0` — empty terminal-sequence	implemented
7.14.2	`('.')//2` — terminal sequence	implemented
7.14.3	`(',')//2` — concatenation	implemented
7.14.4	`(;)//2` — alternative	implemented
7.14.5	`(;)//2` with `(->)//2` — if-then-else	implemented
7.14.6	`('\\|')//2` — second form of alternative	implemented
7.14.7	`{}//1` — grammar-body-goal	implemented
7.14.8	`call//1`	implemented
7.14.9	`phrase//1`	implemented
7.14.10	`!//0` — grammar-body-cut	implemented
7.14.11	`(\+)//1` — grammar-body-not	implemented
7.14.12	`(->)//2` — if-then	implemented

Built-in predicates (clause 8.18)

Clause	Predicate	Status
8.18.1	`phrase/3`	implemented
8.18.1.3	`phrase/2` (bootstrapped as `phrase(GRBody, S0, [])`)	implemented

Prescribed errors (8.18.1.4)

Error	Requirement	EyeProlog
a) `GRBody` is a variable	`instantiation_error`	matches
b) `GRBody` is neither a variable nor callable	`type_error(callable, GRBody)`	matches
c) `S0` is not a terminal-sequence	`type_error(terminal_sequence, S0)` — implementation-defined for `phrase/3`, required for `phrase/2`	diverges: EyeProlog raises `type_error(list, S0)`
d) `S` is not a terminal-sequence	`type_error(terminal_sequence, S)` — implementation-defined	diverges: EyeProlog raises `type_error(list, S)`

Open divergence. EyeProlog performs both optional checks — which the draft permits, and which for phrase/2 clause c it requires — but reports type_error(list, Culprit) where the 2023-08-14 draft specifies type_error(terminal_sequence, Culprit). The draft is explicit that if a processor offers these errors, “their form and consequence must be the following”, so the form is not left open even though performing the check is.

This appears to track an earlier edition, in which these clauses were numbered 8.18.1.3 g and h and specified list. The behaviour is deliberate and covered by a dedicated regression matrix, so changing the error term is a decision to take explicitly rather than a bug to patch silently. Until it is taken, this row is the one known Part 3 deviation.

What the regression matrix does pin, independently of the error term: the same diagnostic across both arities, both sequence positions, atomic and compound non-lists, and improper lists at several depths; the culprit is the whole invalid argument, including an improper list, not just its tail; variables, proper lists, and partial lists are accepted; and for otherwise valid grammar bodies, validation precedes execution even when the grammar would fail or produce a side effect. The upstream phrase quads permit both checking and non-checking outcomes and so do not establish this consistency on their own.

Language concepts

Clause	Concept	Status
7.4.4	grammar rules in Prolog text	implemented
7.5.1	grammar-rule expansion during preparation	implemented
7.13.1	terminals and non-terminals	implemented
7.13.2	format of grammar rules	implemented
7.13.3	semicontext (pushback)	implemented — `head, [Pushback] --> Body`
7.13.4	non-terminal indicator `A//N`	implemented — accepted in module export lists
7.15	executing clauses expanded from grammar rules	implemented
5.5.2	predefined operators	implemented — `-->` is predeclared in both profiles; it is grammar syntax only in normal mode

predicate_property/2 does not appear in the 2023-08-14 draft, so no Part 3 predicate-property extension is claimed here. See ISO-PART2.md for the Part 2 status of that predicate.

Executable evidence

Grammar expansion, sequence validation, grammar-body callability, variable-body instantiation errors, and phrase/3 steadfastness are under focused tests in test/run-regression.mjs and the conformance corpus. The live Neumerkel gate covers the upstream phrase quads.

Changes intended to advance a formal Part 3 claim should update this ledger and the corresponding error cases rather than silently changing the compatibility profile.