1. Visualizing Type Error Messages Allison Thompson CSCI 5535 Spring 2010

2. Motivation This expression has type int but is here used with type float This expression has type my_type but is here used with type my_type

3. Outline  Motivation  Tools: Processing and S EMINAL  ViSeR  Conclusion

4. Outline  Motivation  Tools: Processing and S EMINAL  ViSeR  Conclusion

5. Pros and Cons of Processing  Easy  Didn’t require learning new language  Free  Based on Java 1.4.2 (limited)  Does not always run very fast  Visualization can take 4-5 sec to load; then 4-5 for each refresh

6. S EMINAL : Searching for Error Messages IN Advanced Languages  Enumerate local changes to abstract syntax tree that may remove type errors  Search for places to try changes  Use type checker to evaluate changes  Rank changes and present to user

7. S EMINAL Results: ------------------------------------------------------------------ File "test1.ml", line 1, characters 4-7: This expression has type float but is here used with type int Relevant code: 2.5 ------------------------------------------------------------------ File "test1.ml", line 1, characters 4-7: Try replacing 2.5 with 2.5; [[...]] of type int within context 1 + (2.5; [[...]]);; ============================== File "test1.ml", line 1, characters 2-3: Try replacing + with +; [[...]] of type int -> float -> 'a within context (1 +; [[...]] 2.5);; ============================== 1 + 2.5;; File "test1.ml", line 1, characters 4-7: Try replacing 2.5 with 2.5; [[...]] of type int within context 1 + (2.5; [[...]]);; wildcard replacement with type int

8. Outline  Motivation  Tools: Processing and S EMINAL  ViSeR  Conclusion

9. ViSeR: Visualization for Seminal Results  Goals:  Put Seminal suggestions in context with some form of helpful visualization  Minimize need for user to learn new symbols/etc – improve usability and understandability  Avoid re-introducing confusion: This expression has type int but is here used with type float

10. ViSeR: Examples and Screenshots 1 + 2.5;; This expression has type int but is here used with type float File "test1.ml", line 1, characters 4-7: Try replacing 2.5 with 2.5; [[...]] of type int within context 1 + (2.5; [[...]]);; wildcard replacement with type int

11. ViSeR: Examples and Screenshots This expression has type my_type but it used with type my_type Multiple definition of the type name my_type. Names must be unique in a given structure or signature. ocamlc

12. ViSeR: Examples and Screenshots actual error error location according to OCaml This expression has type int but is here used with type float

13. Outline  Motivation  Tools: S EMINAL and Processing  ViSeR  Conclusion

14. Conclusion  Success?  Put S EMINAL results in context  Provide improvement in usability  Remaining Issues/Future Work  ViSeR as a tool is limited/slow  Several situations doesn’t cover; doesn’t gracefully handle proper compilation  4-5 seconds for some visualizations is too slow ✓ ✗

15. Questions?