Add formal EBNF grammar specification for Maya date parser

[Copilot]

The parser has no formal grammar specification. Parsing logic is embedded across 4 layers of state machine code, making it difficult to understand the complete language, identify edge cases, or verify completeness.

Changes

Grammar Documentation (docs/GRAMMAR.md)

Lexical Tokens

• 9 terminal types: NUMBER, WORD, WILDCARD, PERIOD, PLUS, MINUS, HASH, NEWLINE, SPACE
• Character-level definitions following ISO/IEC 14977:1996 EBNF

Syntactic Grammar

expression     ::= operation | fullDate | calendarRound | longCount
calendarRound  ::= tzolkin WS+ haab
longCount      ::= lcPart {PERIOD lcPart}
operation      ::= expression WS+ operator WS+ expression

Semantic Constraints

• Tzolkin: coefficients 1-13, 20 valid day names
• Haab: coefficients 0-19 (0-4 for Wayeb), 19 valid month names
• Long Count: base-18 for Winal (position 3), base-20 elsewhere

Ambiguities Resolved

1. Partial Calendar Rounds not allowed at top level
2. Whitespace optional between number/word, required between components
3. Comments only inline (after expression) or standalone (cannot split expressions)
4. Consecutive wildcards (**) tokenize as two separate WILDCARD tokens
5. Empty input and blank lines are valid

Examples

• 50+ examples covering all productions
• Valid/invalid cases with explanations
• Edge cases: 6Manik' 5Mol (no space after number), 8.7.6.5.4.17.2.1 (8-part Long Count)

Diagrams

• 7 ASCII railroad diagrams for visual reference

Coverage

Grammar verified against 85 existing parser tests (100% coverage across layers 0-3).

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Create Formal Grammar Specification</issue_title>
<issue_description>
Parent: Epic: Stabilize Parser & Upgrade to maya-dates >= 1.3.0
Priority: High
Complexity: Medium
Estimated Effort: 16 hours
Labels: documentation, grammar, specification

Description

Document the Maya date parsing grammar in EBNF notation. This serves as the specification for the new parser implementation and helps identify edge cases/ambiguities in the current informal parsing logic.

Problem Statement

The current parser has no formal grammar specification. Parsing logic is embedded across 4 layers of state machine code, making it:

• Hard to understand the complete language
• Difficult to identify edge cases
• Impossible to verify completeness
• Challenging to discuss design decisions

Grammar Coverage

The grammar must document:

1. Calendar Round: tzolkin haab (e.g., 4 Ajaw 8 Kumk'u)
2. Long Count: baktun.katun.tun.winal.kin (e.g., 9.16.19.17.19)
3. Full Date: calendarRound longCount
4. Wildcards: * in any position (* Ajaw 8 Kumk'u, 9.*.10.10.10)
5. Operations: expr (+ | -) expr
6. Comments: # text (inline or standalone)
7. Whitespace: Space, tab handling rules

Deliverables

1. docs/GRAMMAR.md

Create comprehensive grammar document with:

Introduction

• Purpose of the grammar
• Notation conventions (EBNF)
• Reading guide for non-experts

Lexical Tokens

(* Terminals *)
NUMBER     ::= [0-9]+
WORD       ::= [a-zA-Z']+
WILDCARD   ::= '*'
PERIOD     ::= '.'
PLUS       ::= '+'
MINUS      ::= '-'
HASH       ::= '#'
NEWLINE    ::= '\n'
SPACE      ::= ' ' | '\t'

Syntactic Grammar

(* Main productions *)
input          ::= line (NEWLINE line)* NEWLINE?
line           ::= expression comment? | comment | ε

expression     ::= operation | fullDate | calendarRound | longCount

operation      ::= expression WS+ operator WS+ expression
operator       ::= PLUS | MINUS

fullDate       ::= calendarRound WS+ longCount

calendarRound  ::= tzolkin WS+ haab
tzolkin        ::= tzolkinCoeff WS+ tzolkinDay
tzolkinCoeff   ::= NUMBER | WILDCARD
tzolkinDay     ::= WORD | WILDCARD

haab           ::= haabCoeff WS+ haabMonth
haabCoeff      ::= NUMBER | WILDCARD
haabMonth      ::= WORD | WILDCARD

longCount      ::= lcPart (PERIOD lcPart)*
lcPart         ::= NUMBER | WILDCARD

comment        ::= HASH commentText
commentText    ::= [^\n]*

WS             ::= SPACE+

Semantic Constraints

Document validation rules not expressible in grammar:

1. Tzolkin Coefficient: Must be 1-13 (if not wildcard)
2. Tzolkin Day: Must be one of 20 valid day names (if not wildcard)
3. Haab Coefficient: Must be 0-19 (if not wildcard), except Wayeb (0-4)
4. Haab Month: Must be one of 19 valid month names (if not wildcard)
5. Long Count Parts:
   • Baktun: Any non-negative integer
   • Katun, Tun, Winal, Kin: 0-19
   • Winal (position 1): Special base-18 rule
6. Long Count Length: Must be 1-5 parts (partial dates allowed)

2. Examples for Each Production

For every grammar rule, provide 3+ examples:

#### `calendarRound` Examples

**Valid**:
- `4 Ajaw 8 Kumk'u` - Standard calendar round
- `* Ajaw 8 Kumk'u` - Wildcard tzolkin coefficient
- `4 * 8 Kumk'u` - Wildcard tzolkin day
- `4 Ajaw * Kumk'u` - Wildcard haab coefficient
- `4 Ajaw 8 *` - Wildcard haab month
- `** **` - All wildcards

**Invalid** (with explanation):
- `14 Ajaw 8 Kumk'u` - Tzolkin coefficient > 13
- `4 Ajaw 20 Kumk'u` - Haab coefficient > 19
- `4 NotADay 8 Kumk'u` - Unknown tzolkin day name

3. Ambiguity Analysis

Document and resolve ambiguities:

Ambiguity 1: Partial Dates

Issue: Is 4 Ajaw a valid partial calendar round (tzolkin only) or an error?

Current Behavior (from tests):

// layer-1 test shows this is NOT parsed as standalone tzolkin
'4 Ajaw' // Would need to check actual test behavior

Resolution: Document whether partial dates are:

• Option A: Allowed (tzolkin-only or haab-only are valid)
• Option B: Forbidden (must always have both parts or fail)

Ambiguity 2: Whitespace Handling

Issue: How much whitespace is required/allowed between components?

Examples:

• 4 Ajaw 8 Kumk'u - Single space (valid)
• 4 Ajaw 8 Kumk'u - Multiple spaces (valid?)
• 4Ajaw 8Kumk'u - No space between number and word (valid?)

Current Behavior (from tests):

// From layer-0-parser.spec.ts line 137:
['6Manik\' 5Mol', [NT(6), WT('Manik\''), ST, NT(5), WT('Mol'), LET]]
// This suggests no space between number+word IS parsed

Resolution: Specify exact whitespace rules.

Ambiguity 3: Comment Placement

Issue: Can comments appear anywhere?

Examples:

• 4 Ajaw 8 Kumk'u # comment - After full date (valid)
• # comment\n4 Ajaw 8 Kumk'u - Standa...

• Fixes Create Formal Grammar Specification #18

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