The goal of the Bug Explainer is to provide a web service for novice programmers encountering bugs in their code when learning a new language. Novices don't know what's going wrong, and they often describe their problems in vague or invalid terms, e.g., "member doesn't work!" Hence their attempts to find answers via Google or FAQ searches often fail to find relevant answers.
To get around the ambiguity problem,
- the front-end tells novices to enter concrete details of their problem, rather than their (often incorrect) interpretation of the problem
- a set of rules analyzes the bug report and finds potential explanations
Tasks
Bug Report Interface
The input interface is where the end user specifies a problem. The interface needs to be easy to use and not require any expert knowledge from the user.
Using Webactions, create a simple readable form that lets a user specify the following information:
| Summary | A short text summary of bug. Not useful for the computer. |
|---|---|
| Input | Sample code that produces the bug |
| Expected | the result(s) the user expected to see |
| Actual | the result(s) the user actually saw |
| Operating System | the operating system the user is on |
| Language | the language, including implementation version the user has |
Here are two example bug reports. I'm leaving out the summaries and platform information, since they're not important here:
| Input | (LET ((L '(A B C))) (DELETE 'A L) L) |
|---|---|
| Expected | (B C) |
| Actual | (A B C) |
| Input | (DELETE '(B) '((A) (B) (C)) |
|---|---|
| Expected | ((A) (C)) |
| Actual | ((A) (B) (C)) |
Submitting the form should cause the server to
- create an instance of a bug report with the relevant data and a unique ID
- persist this in a file
- redirect the client to a bug explanation page that shows the bug and the explanations, if any
In good RESTful form, the URL for the new page should be bookmarkable. This bug page would also contain any automated explanations, but for now of course none will be found.
Implement and test with at least the two examples above.
Submit: the Webactions functions you defined to implement to create and store the bug reports. Do not submit the CLP pages, but do submit functions called by CLP tags to display the bug reports, if any were defined.
Bug Analyzer
The analyzer needs to look at the bug report and find possible explanations for the bug. The clues to common bugs can be subtle. For example, novices often report that deleting doesn't work, and their example involves deleting the first element of a list.
The standard way to look for such clues is pattern matching. The matcher used in the Lisp Critic is a good fit, since it's been tested on matching many Lisp code constructs. One pattern that recognizes the "deleting first element" situation is:
| Input | (?CONTAINS (DELETE ?*)) |
|---|---|
| Expected | ((?* X)) |
| Actual | ((? Y) (?* X)) |
| Explanation | Although DELETE can return a list without the first element, the structure of Lisp lists make it impossible to destructively remove the first element of a list. For more, see http://www.cs.cmu.edu/Groups/AI/html/faqs/lang/lisp/part3/faq-doc-4.html |
Note the use of variables across several fields.
Bug Report #1 is an example of a report that this pattern should match.
Bug Report #2 is an example of a report of a bug due to a different
misunderstanding of DELETE. What's the explanation, and what's a
pattern to recognize relevant reports?
If you're not comfortable with packages yet, do all of the code in CS325-USER. Otherwise, define a BUG-FINDER package for the code and a BUG-FINDER-TESTS package for the test cases.
- Define a macro
DEFBUGsuch that (defbug name pattern text) defines a bug explanation rule. Each rule has an internal name, a pattern to match against the parts of a bug report, and a text string with a brief explanation of the problem. The string might contain HTML, specifically a link to the Lisp FAQ or other useful pages. - Define at least the two DELETE bug explanations referred to above.
- Use
DEFINE-TESTto define some test cases for the (undefined!) functionGET-EXPLANATIONSthat verify that (get-explanations bug-report) returns the correct explanation rules for some input patterns. Be sure to test for inputs that match 0, 1 or several rules.
Verify that the tests fail. - Define a function
GET-EXPLANATIONSand get it to pass your test cases.. - Modify your your bug explanation page
to use
GET-EXPLANATIONSto find and display the texts of any explanation rules that apply.
DEFBUG is similar to DEFINE-LISP-PATTERN
used in defining Lisp Critic rules in
lisp-rules.lisp. You need
some format that identifies which fields are being matched against, i.e.,
input versus expected versus actual.
GET-EXPLANATIONS should return rules, not just the text strings.
There's no additional work to do this, and it leaves your options
open for extensions, such as editing rules in the next task.
Submit: the Webactions functions you defined to implement to create and store the bug reports. Do not submit the CLP pages, but do submit functions called by CLP tags to display the bug reports, if any were defined.
Bug Rule Editor
Modify your your bug explanation page to allow people to edit an existing explanation rule, or to add a new one. The exact interface is up to you, but either option should open the same rule editing form, to let people change the pattern and explanation text, but not the name.
Submit: the Webactions functions you defined to implement to back-end editing and updating. Do not submit the CLP pages, but do submit functions called by CLP tags to display the bug reports, if any were defined.