Validate PILES Notation

Parse and validate PILES notation strings for puzzle piece fusion groups.

When to Use

• Validating user-supplied PILES strings before passing to generate_puzzle()
• Debugging fusion group issues (wrong pieces merged, unexpected results)
• Explaining PILES notation to users in plain language
• Testing round-trip fidelity: parse -> groups -> serialize -> parse

Inputs

• Required: PILES notation string (e.g., "1-2-3,4-5")
• Optional: Puzzle result object (for adjacency validation and keyword resolution)
• Optional: Puzzle type (for keyword support like "center", "ring1", "R1")

Procedure

Step 1: Syntax Validation

library(jigsawR)
result <- validate_piles_syntax("1-2-3,4-5")
# Returns TRUE if valid, error message if invalid

Check for common syntax errors:

• Unmatched parentheses: "1-2(-3)-4" with mismatched ()
• Invalid characters: only digits, -, ,, :, (, ) and keywords allowed
• Empty groups: "1-2,,3-4" (double comma)

Expected: TRUE for valid syntax, descriptive error for invalid.

On failure: Print the exact PILES string and the validation error message.

Step 2: Parse into Groups

groups <- parse_piles("1-2-3,4-5")
# Returns: list(c(1, 2, 3), c(4, 5))

For strings with ranges:

groups <- parse_piles("1:6,7-8")
# Returns: list(c(1, 2, 3, 4, 5, 6), c(7, 8))

Expected: List of integer vectors, one per fusion group, with correct piece IDs and group boundaries.

On failure: Check that the PILES string passed syntax validation in Step 1 first. If parsing returns unexpected groups, verify that - separates pieces within a group and , separates groups, and that range notation (:) expands to inclusive endpoints.

Step 3: Explain in Plain Language

Describe each group for the user:

• "1-2-3,4-5" -> "Group 1: fuse pieces 1, 2, and 3. Group 2: fuse pieces 4 and 5."
• "1:6" -> "Group 1: fuse pieces 1 through 6 (6 pieces)."
• "center,ring1" -> "Group 1: center piece. Group 2: all pieces in ring 1."

Expected: Each fusion group is described in plain language with piece counts and identifiers, making the notation understandable to non-technical users.

On failure: If keywords cannot be explained (e.g., "ring1" has no clear meaning), the notation may require a puzzle result object for context. Advise the user to provide the puzzle type or use numeric piece IDs instead.

Step 4: Validate Against Puzzle Result (Optional)

If a puzzle result object is available, verify:

# Generate the puzzle first
puzzle <- generate_puzzle(type = "hexagonal", grid = c(3), size = c(200))

# Parse with puzzle context (resolves keywords)
groups <- parse_fusion("center,ring1", puzzle)

Check:

• All piece IDs exist in the puzzle
• Keywords resolve to valid piece sets
• Fused pieces are actually adjacent (warning if not)

Expected: All piece IDs valid. Adjacent pieces fuse cleanly.

On failure: List invalid piece IDs or non-adjacent pairs.

Step 5: Round-Trip Serialization

Verify parse/serialize fidelity:

original <- "1-2-3,4-5"
groups <- parse_piles(original)
roundtrip <- to_piles(groups)
# roundtrip should equal original (or canonical equivalent)

groups2 <- parse_piles(roundtrip)
identical(groups, groups2)  # Must be TRUE

Expected: Round-trip produces identical group lists, confirming that parsepiles() and topiles() are inverses.

On failure: If round-trip differs, check whether the serializer normalizes the notation (e.g., sorting piece IDs or converting ranges to explicit lists). Canonical differences are acceptable as long as identical(groups, groups2) returns TRUE.

PILES Quick Reference

# Basic syntax
"1-2"           # Fuse pieces 1 and 2
"1-2-3,4-5"     # Two groups: (1,2,3) and (4,5)
"1:6"           # Range: pieces 1 through 6

# Keywords (require puzzle_result)
"center"        # Center piece (hex/concentric)
"ring1"         # All pieces in ring 1
"R1"            # Row 1 (rectangular)
"boundary"      # All boundary pieces

# Functions
parse_piles("1-2-3,4-5")                    # Parse PILES string
parse_fusion("1-2-3", puzzle)               # Auto-detect format
to_piles(list(c(1,2), c(3,4)))              # Convert to PILES
validate_piles_syntax("1-2(-3)-4")          # Validate syntax

Validation

• validatepilessyntax() returns TRUE for valid strings
• parse_piles() returns correct group lists
• Round-trip serialization preserves groups
• Keywords resolve correctly with puzzle context
• Invalid syntax produces clear error messages

Common Pitfalls

• Keyword without puzzle context: Keywords like "center" require a puzzle result object. Pass it to parsefusion(), not parsepiles().
• 1-indexed pieces: Piece IDs start at 1, not 0.
• Adjacent vs non-adjacent fusion: Fusing non-adjacent pieces works but may produce unexpected visual results. Validate adjacency when possible.
• Range notation: "1:6" includes both endpoints (1, 2, 3, 4, 5, 6).

Related Skills

• generate-puzzle — generate puzzles with fusion groups
• add-puzzle-type — new types need PILES/fusion support
• run-puzzle-tests — test PILES parsing with the full suite