name: paren-debug
description: Debug parenthesis balance issues in Scheme files. Invoke when encountering "unexpected end-of-file reading list" or "unexpected close parenthesis" errors, or when manually counting parens.
allowed-tools: Bash(scheme:, ./fold:), Read, Grep

Paren Debug Skill

When to Use

Invoke this skill when you encounter:
- Exception in read: unexpected end-of-file reading list at line N
- Exception in read: unexpected close parenthesis at line N
- Any situation where you're manually counting parentheses
- After editing Scheme code and getting parse errors

Tools Available

paren-locate - Primary Tool (Stack-Based)

The most useful tool. Shows exact locations of paren errors:

scheme -q <<'EOF'
(load "boundary/tools/paren-check.ss")
(paren-locate "path/to/file.ss")
EOF

Output format is compiler-friendly (file:line:col):

path/to/file.ss:46:1: error: unclosed '(' - never closed
path/to/file.ss:61:19: error: mismatched brackets: opened '[' at line 61 col 12, closed with ')'

paren-ok? - Quick Check

Returns #t if file is balanced, #f otherwise:

scheme -q <<'EOF'
(load "boundary/tools/paren-check.ss")
(paren-ok? "path/to/file.ss")
EOF

paren-errors - Programmatic Access

Returns list of error structs for further processing:

scheme -q <<'EOF'
(load "boundary/tools/paren-check.ss")
(paren-errors "path/to/file.ss")
EOF

paren-check - Legacy Balance Report

Line-by-line balance report (less precise but shows running totals):

scheme -q <<'EOF'
(load "boundary/tools/paren-check.ss")
(paren-check "path/to/file.ss")
EOF

./fold -c / ./fold --check-syntax - Quick CLI Check

Fast paren check from command line (no daemon needed):

./fold -c path/to/file.ss
./fold --check-syntax path/to/file.ss

Output:

# Success:
path/to/file.ss: ✓ All parentheses balanced

# Error:
path/to/file.ss:46:1: error: unclosed '(' - never closed

Exit codes: 0 = balanced, 1 = errors found.

Workflow

1. When you see a paren error: Run paren-locate first
2. Read the error location: The output tells you exactly which opener was never closed
3. Fix at the source: Go to the reported line/column and add the missing closer
4. Verify: Run paren-ok? to confirm the fix

Example Session

# 1. You edited exports.ss and get:
#    Exception in read: unexpected end-of-file reading list at line 46

# 2. Run paren-locate
scheme -q <<'EOF'
(load "boundary/tools/paren-check.ss")
(paren-locate "boundary/introspect/exports.ss")
EOF

# Output:
# boundary/introspect/exports.ss:46:1: error: unclosed '(' - never closed

# 3. The error is at line 46, column 1 - that's where the unclosed ( is!
#    NOT at the end of the file where Scheme complained.

# 4. Fix and verify:
scheme -q <<'EOF'
(load "boundary/tools/paren-check.ss")
(paren-ok? "boundary/introspect/exports.ss")
EOF
# Output: #t

Error Types Detected

Tips

• Don't count parens manually - always use paren-locate
• The error location is where to fix - unlike Scheme's error which points to where the list started
• Check after every significant edit - catch errors early
• Mismatch detection - the tool catches (foo] style errors that pure counting misses

File Location

boundary/tools/paren-check.ss - Load this to access all paren-checking functions.