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Brent Site Admin
Joined: 01 Jul 2005 Posts: 763

Posted: Apr 21st, 2012, 5:40pm Post subject: Experiment  Units of measure 


VF will have support for units of measure. This means that instead of using raw numbers for things such as angles in radians in trig functions, VF will require the programmer to specify the unit when one is expected by a function, et cetera. This may sound onerous at first, but it offers some advantages such as automatic conversion if the given unit is in the same "dimension" as the expected unit.
The syntax is still a little rough around the edges, but works like this. The Base Unit statement defines a dimension and specifies its base unit from which other units can be derived. The Unit statement defines a unit and may include a conversion formula. There are ways to specify (1) that the unit is defined by the SI; (2) aliases, such as meter vs metre and meter vs meters vs m. A consequence of declaring an SI unit is the automatic creation of conversion factors of 10 with the standard prefixes, such as Kilometer and km. While VF's keywords and identifiers are caseinsensitive, units are casesensitive, just as they are in the real world.
Rather than giving the grammar, I'll just post my test file for you all to look over and give your opinions about it. Code:  module StdUnits
base unit length in meters
unit meter(s) metre(s) m
unit inch(es) = 2.54cm
unit foot feet ft = 12inches
unit yard(s) yd(s) = 3feet
unit mile(s) mi = 5280feet
unit light_year(s) ly = 9.4605284 petameters
base unit time in seconds
unit second(s) sec(s) s
unit minute(s) min(s) m = 60secs
unit hour(s) h = 60mins
base unit speed in meters/second = length/time
unit MPH = miles/hour
base unit angle in radians
unit radian(s) rad
unit degree(s) deg = 0.0174532925 radians
unit gradian(s) grad = 0.9 degrees
base unit temperature in Kelvin
unit Kelvin K
unit degree_C degrees_C += 273.15 Kelvin
unit degree_F degrees_F = 1.8 degrees_C + 32
unit Rankine R = (0 degrees_C + 273.15) * 1.8
base unit area in meters2 = meters * meters
unit meter2 meters2 metre2 metres2 m2
unit hectare ha = 10000 meters2
unit square_foot square_feet sq_ft = 0.09290304 meters2
base unit seconds_squared in seconds2 = seconds * seconds
unit second2 seconds2 sec2 secs2 s2
base unit acceleration in meters/second2 = length/time/time
unit Earth_gravity g = 9.80665 m/s2
base unit mass in kilograms
unit gram(s) g
unit metric_ton(s) metric_tonne(s) t = 1000 kilograms 
_________________ Brent 

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STPendl Full Member
Joined: 20 Aug 2007 Posts: 161 Location: Austria

Posted: Apr 21st, 2012, 7:24pm Post subject: Re: Experiment  Units of measure 


Code: 
unit degree_F degrees_F = 1.8 degrees_C + 32
unit Rankine R = (0 degrees_C + 273.15) * 1.8

Isn't there an asterisk missing between 1.8 and degrees_C, similar in the second line after zero?
The rest has to sink in, but it seems to be a good addition. _________________ Stefan
Any code I post can be freely used, just give credit. 

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Brent Site Admin
Joined: 01 Jul 2005 Posts: 763

Posted: Apr 21st, 2012, 9:56pm Post subject: Re: Experiment  Units of measure 


Yes, that does look incorrect and I'm not certain what syntax would be clean and correct. My syntax is based on Fortress, but I'm having trouble finding a source file that may have these units defined.
For comparison, another current language that supports units is F#. However F# doesn't have a concept of a "base unit", so conversions must be written to go both ways. Code:  [<Measure>] type degC // temperature, Celsius/Centigrade
[<Measure>] type degF // temperature, Fahrenheit
let convertCtoF ( temp : float<degC> ) = 9.0<degF> / 5.0<degC> * temp + 32.0<degF>
let convertFtoC ( temp: float<degF> ) = 5.0<degC> / 9.0<degF> * ( temp  32.0<degF>)
// Define conversion functions from dimensionless floating point values.
let degreesFahrenheit temp = temp * 1.0<degF>
let degreesCelsius temp = temp * 1.0<degC> 
_________________ Brent 

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Brent Site Admin
Joined: 01 Jul 2005 Posts: 763

Posted: Apr 22nd, 2012, 1:01am Post subject: Re: Experiment  Units of measure 


All I can find of Fortress are Code:  dim Temperature SI_unit kelvin kelvins K_  in one file, and in another Code:  (* We assume that an absolute temperature of 0 degrees Smurdley is the same as
an absolute temperature of 0 degrees Celsius. Then a relative temperature
of 1 degree Smurdley is 27/100 degree Celsius = 0.27 kelvin. *)
unit degreeSmurdley: Temperature = 0.27 kelvin  which isn't much help.
So I then looked up what Frink does. http://futureboy.us/frinkdata/units.txt which defines temperature units, but gives the caveat that they should only be used with calculations involving changes in temperature. A conversion between different scales requires a function call. _________________ Brent 

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STPendl Full Member
Joined: 20 Aug 2007 Posts: 161 Location: Austria

Posted: Apr 22nd, 2012, 7:17am Post subject: Re: Experiment  Units of measure 


I was wondering what the term "1.8 degrees_C" would do.
0° Kelvin is the absolute zero temperature, so this is the base, which is understandable.
Conversion from 0° Kelvin to 0° Celsius is done by adding 273.15 this I have been taught too.
But conversion from 0° Celsius to 0° Fahrenheit is where I get stuck, so does the line tell us that "1.8°C + 32 = 33.8°C" are 0° Fahrenheit? _________________ Stefan
Any code I post can be freely used, just give credit. 

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Brent Site Admin
Joined: 01 Jul 2005 Posts: 763

Posted: Apr 22nd, 2012, 6:34pm Post subject: Re: Experiment  Units of measure 


Based on what other languages are doing, I have decided to do some sort of quasifunction syntax. However, I'm not sure where to place the parameter, before the name(s) of the unit or after. The first way more resembles how the unit is used, but puts a bit of "noise" up front. Do any of you have an opinion on which is more readable?
Code:  ' #1
unit [k in Kelvin] degree_C degrees_C = k+273.15
unit [c in degrees_C] degree_F degrees_F = 1.8*c+32
unit [k in Kelvin] Rankine degree_R degrees_R = 1.8*k
' #2
unit degree_C degrees_C [k in Kelvin] = k+273.15
unit degree_F degrees_F [c in degrees_C] = 1.8*c+32
unit Rankine degree_R degrees_R [k in Kelvin] = 1.8*k 
_________________ Brent 

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STPendl Full Member
Joined: 20 Aug 2007 Posts: 161 Location: Austria

Posted: Apr 22nd, 2012, 7:25pm Post subject: Re: Experiment  Units of measure 


I think #1 is better, since the variable declaration is placed before the unit definition, which in turn is more an expression than a declaration. _________________ Stefan
Any code I post can be freely used, just give credit. 

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