Troubleshooting

Common issues and how to resolve them.

Parse Errors

"Unknown keyword" Error

SPL parse error: Unknown keyword: defeasible

Cause: Wrong keyword.

Fix: Use correct SPL keywords:

• given (not fact)
• normally (not defeasible)
• always (not strict)
• except (not defeater)

Unexpected Conclusions

Expected Conclusion Missing

Symptom: A literal you expected to be +d is -d.

Debugging steps:

1. Check if the rule exists:

   spindle stats theory.spl
   

2. Check if the body is satisfied:

   ; Is 'bird' actually proven?
   (normally r1 bird flies)
   

3. Check for conflicts:

   # Look for rules proving the complement
   grep "(not flies)" theory.spl
   

4. Check superiority:

   # Is there a superior rule blocking?
   grep "prefer" theory.spl
   

Unexpected Conclusion Present

Symptom: A literal is +d when it shouldn't be.

Debugging steps:

1. Find which rule proves it:

   grep "literal" theory.spl
   

2. Check if a defeater is missing:

   ; Add a defeater to block
   (except d1 exception unexpected-literal)
   

Both Literals Unprovable (Ambiguity)

Symptom: Neither q nor (not q) is +d.

Cause: Conflicting rules without superiority.

Fix: Add superiority:

(normally r1 a q)
(normally r2 b (not q))
(prefer r1 r2)    ; or (prefer r2 r1)

Superiority Issues

Superiority Not Working

Symptom: Declared (prefer r1 r2) but r2 still wins.

Check:

1. Rule labels match exactly:

   (normally r1 bird flies)
   (normally r2 penguin (not flies))
   (prefer r1 r2)                      ; Must match labels exactly
   

2. Rule type compatibility:

   • Superiority only affects defeasible rules and defeaters
   • Strict rules always win regardless of superiority

3. Both rules actually fire:

   # Both bodies must be satisfied
   spindle reason --positive theory.spl | grep "bird\|penguin"
   

Circular Superiority

; BAD: creates undefined behavior
(prefer r1 r2)
(prefer r2 r1)

Fix: Remove one declaration or restructure rules.

Grounding Issues

Variables Not Matching

Symptom: Rules with variables don't produce expected results.

Check:

1. Facts use predicates:

   ; Wrong: not a predicate
   (given parent-alice-bob)
   
   ; Right: predicate with arguments
   (given (parent alice bob))
   

2. Variable positions match:

   ; Fact: (parent alice bob)
   ;              ?x    ?y
   
   ; Rule must match positions
   (normally r1 (parent ?x ?y) (ancestor ?x ?y))
   

3. All head variables appear in body:

   ; INVALID: ?z not in body
   (normally r1 (parent ?x ?y) (triple ?x ?y ?z))
   

Grounding Explosion

Symptom: Memory exhaustion or very slow reasoning.

Cause: Too many variable combinations.

Fix:

• Add constraints to rule bodies
• Break large joins into smaller rules
• Add explicit superiority where conflicts are expected

File Format Issues

Wrong Format Detection

Symptom: File parses incorrectly.

Fix: Use .spl extension for SPL format.

Encoding Issues

Symptom: Special characters cause errors.

Fix: Use UTF-8 encoding.

Conflict Expectations

Conflicting Defeasible Rules Both Show As Provable

Symptom: You see both +d p and +d ~p.

Cause: No superiority relation resolves the conflict.

Fix:

1. Add an explicit superiority declaration between the conflicting rules.
2. Re-run reasoning and verify only the preferred side remains +d.

Performance Issues

Slow Reasoning

Check:

1. Theory size: spindle stats theory.spl
2. Conflict graph: add superiority to resolve high-conflict hotspots
3. Grounding: check for variable explosion
4. Conflicts: add superiority to reduce ambiguity

Memory Exhaustion

Causes:

• Too many ground rules (variable explosion)
• Very long inference chains
• Large number of conflicts

Fixes:

• Reduce variable combinations
• Restructure theory

Debugging Tips

Validate First

Always validate before reasoning:

spindle validate theory.spl && spindle reason theory.spl

Minimal Reproduction

Create a minimal theory that reproduces the issue:

; Start with just the failing rules
(given bird)
(normally r1 bird flies)
; Add rules until issue appears

Use Positive Output

Focus on what IS proven:

spindle reason --positive theory.spl

Check Statistics

spindle stats theory.spl

Look for unexpected counts.

Enable Logging

SPINDLE_LOG=debug spindle reason theory.spl 2>&1 | less

Getting Help

If you can't resolve an issue:

1. Create a minimal reproduction
2. Include the theory file
3. Show expected vs actual output
4. Report at: https://codeberg.org/anuna/spindle-rust/issues