Skip to main content

F# and Units of Measure

On Channel 9 they have an interview with Andrew Kennedy about the new Unit of Measure feature in F#.

This is a really cool feature and I have plans to use it, however there is one problem I have with it: The UOM information is baked into the compiler and can't be persisted.

An example that Andrew uses it the NASA's Mars Climate Orbiter that crashed due to an issue with Units of Measure (long story short the program thought it was using Newtons when it was actually using Pounds Force). This is a good example of how when you are doing calculations it would be nice if something other than the brain of the programmer was checking the units. But there is another time that UOM is important: When inputting the data.

I recently worked on an application where the units for a given value could be in English or SI (metric) units and we had an elaborate system to deal with them. The end user could even come up with their own unit system if they wanted to and the application had to be able to handle that.

Internally and for storage we degreed that all units would be in metric, no If's And's or But's about it. It was only when we displayed the values to the end user did we convert it to their chosen unit system. And for importing data we required that the imported values have their UOM indicated.

The F# UOM feature is a truly remarkable step in solving one of my pet issues. The next step will have to include a way to persist the UOM information with the data to any data store because without this there is no way to guarantee that the data values coming in are really what we say they are.


Popular posts from this blog

Json for jqGrid from ASP.Net MVC

jqGrid takes a specific format for its json (taken from jqGrid documentation): [js]{ total: "xxx",page: "yyy", records: "zzz", rows : [ {id:"1", cell:["cell11", "cell12", "cell13"]}, {id:"2", cell:["cell21", "cell22", "cell23"]}, ... ]}[/js] The tags mean the following: total - Total number of Pages. page - Current page Index. records - Total number of records in the rows group. rows - An array with the data plus an identifier. id - The unique row identifier, needs to be an int from what I have found. cell - An array of the data for the grid. The ASP.Net MVC framework has the JsonResult response type which we can use to populate the jqGrid. As an example I created a Person model and a method to return some data: [csharp] public class Person { public int ID { get; set; } public string Name { get; set; } public DateTime Birthday { get; set; } } public I

Remote Controlled RoboTank

This is my version of the ever popular to build RoboTank. It uses an Arduino Mega 2560 with the AdaFruit motor shield and an XBee S1 to communicate to the DFRobot Gamepad. The sketch for the RoboTank makes use of the AFMotor.h to drive the motors and includes a serial parser to read and process the commands coming from the Gamepad. DFRobot Wireless Joystick

Changing Typed DataSet Connection String

I was working on a WinForm app that connected to a MS Access database. Yeah, Access sucks but I didn't have a choice in the matter. The app itself is used to import a bunch of CSV files into the Access database. It is more of a utility program and it has going through several variations, from being a simple hand driven command line tool to being GUI driven. The command line version was all hand controlled. I had to go in and update configuration files to point to the CSV files and the MDB database. That got old fast so I decided to make a GUI version that would allow me to pick the MDB file and each of the CSV files to import. Picking and using the CSV files was easy, it was changing the connection string for the MDB that proved to be the hardest. I am using strongly typed datasets in VS2005. If you have ever worked with them you find out soon that the connection string gets saved with the project in the app.config file, even if it is a seperate DAL dll project. My guess is