Group-By Refactor

As always, as soon as I release a library, I can see all the mistakes I was happy leaving in until other people could see it. In Group-By I found all sorts of inconsistencies in my approach, and so to make this tiny library better I rewrote the important bits. The main problem was that this started as an alist grouping mechanism. But alists became untenable at depths greater than 1 or 2, or if linear lookup was unacceptably slow. For more efficiency I had looked at grouping into hash table; for a usable interface I looked at grouping into CLOS tree-nodes. Then I combined all three approaches into a monstrosity. The problem with this approach was that it conflated wanting a nice/usable interface (which CLOS can provide), with the efficiency issues of looking up children via a hash table or list. As such I had this strange mirroring of awful to use datastructure backends, barely wrapped in a nicer CLOS interface.

No more, now the structure of multiple groupings is a CLOS tree of grouped-list objects, while the children are stored in a single hashtable or list on each tree node (with methods defined so you should never have to worry about the implementation other than to adjust performance). This greatly simplified my ability to think about what this library was doing, and cleaned up what I considered to be some fairly glaring ugliness. Overall i think this refactoring was a victory.

It would be nice to switch implementations from list to hashtable when we noticed the number of children increasing past a certain threshold, but I have left that for a later date.

Group-By: A Common Lisp library to help group data into trees

A recurring problem I have experienced while programming, is the need to convert a flat list of data into a more complex tree data structure. This is especially common when dealing with results from relational databases (where all data is intrinsically flat, and queries return tables of data). To solve this problem I wrote a small library named group-by (in honor of the sql operator that performs much the same task).

The easiest example:

(group-by '((a 1 2) (a 3 4) (b 5 6)))
=> ((A (1 2) (3 4)) (B (5 6)))

A more concrete example is from trac, the ticketing system we use. Trac tickets contain fields for author, project, milestone, and summary (among others). When displaying this data, my project manager wants to be able to see what everybody is working on (a tree view organized by author, project, and milestone), as well as being able to see what is being worked on in a project and by whom (a tree view organized by project and milestone). To accomplish this I pull a flat list of ticket objects from the database (using a clsql-orm generated class). I then create a tree from this data table by calling make-grouped-list. I can then perform a standard recursive tree walk to render this with the desired organization directly.

Example Call:
(make-grouped-list tickets
:keys (list #'author #'project #'milestone)
:tests (list #'equal #'equal #'equal))

Example Rendering:

Group-by supports grouping into alists, hashtables, and CLOS tree-nodes. To hide the difference between these implementations, I created a grouped-list CLOS object that manages all of the grouping and presents a unified interface to each of these implementation strategies. I support each of these implementations because which to use is strongly dependent on the workload you anticipate performing with the tree. Simply grouping once then recursively rendering the tree, is often more efficient as an alist, than a heavier weight data structure. Conversely, hashtables tend to perform better for lots of accesses into the grouping structure.

To see more, runnable examples, please checkout the project page and the examples file.

CL-Creditcard & CL-Authorize-net: Processing credit card payments with common lisp

I just pushed cl-creditcard to my github account. CL-Creditcard( and sub-library cl-authorize-net) is a library that we use to process payments with Authorize.Net. We have a large internal application that tracks and manages all our business and customer logic including billing and invoicing. (Invoices are generated using cl-typesetting). This application charges credit card payments through this cl-authorize-net.

It has been stable and charging cards for years and I just got around to releasing it. Soon it will also support ACH (echeck) transactions and we will be moving to lisp-unit from lift.

As with all payment processing, test very well before putting into production :)

CLSQL-ORM: Turn you existing database schema into Common Lisp CLSQL-View-Classes

CLSQL-ORM is a common lisp library I just pushed to my git hub account. Its primary goal is to generate CLSQL-view-classes based on an existing database. It uses the “information_schema” views to introspect relevant data from the database, then builds and evals the view-class definitions. This project is a significant branch of clsql-pg-introspect, attempting to remove its “pg” aspects in favor of the standard “information_schema”. It might have changed some semantics/conventions along the way, (I’m not sure as I didn’t use the original project much, and that was long ago).

I wanted to generate my lisp objects from the database for a couple reasons. One, I am fairly comfortable with SQL databases and am used to specifying them in whatever variant of sql the database engine supports. Two, I am most often presented with an extant working database that I want to interact with (such as a wordpress install), where the schema of the database can change, and I just want my common lisp to match whatever the database says, rather than trying to keep both up to date with each other manually. Obviously this project encodes many of my own, personal thoughts and tastes about databases, which may not be the same as your thoughts and tastes. This project is perhaps best though of as a jumping off point for creating your own personal common lisp ORM, though it should be usable as is, if your tastes and mine coincide.

Symbol-Munger: A common lisp library to help convert symbols between their representations in various systems

I just posted a small common lisp library to my github account named Symbol-Munger. Symbol-Munger provides functionality to ease conversion between the same symbol in different environments.

For example, when generating common lisp classes from a database schema, I want to change column names into lisp slot / accessor names, and then later when I am displaying that common lisp slot on the screen I want to display its slot-name as an english column header. (IE: my_db_col > my-db-col > My Db Col)

I have had this code laying about for years and use it everywhere frequently. Earlier today while cleaning other code, I ran across this TODO in vana-inflector, and realized I already had code that performed this function. This library contains one function that does the bulk of the work (normalize-capitalization-and-spacing) and many functions that set default arguments to that one (lisp->english, english->camel-case, english->keyword. etc). Its only dependency is iterate.