Here's an updated instance of that code -- this time dealing with
subtraction (thanks to Dan Bron).
Note also that perhaps I should instead just define replacement
operators for + - * % but this approach works:
units=:3 :0"0&;:
assert._1-:nc y ['new unit name must have no other meaning'
L1=. 'assert.0=#$0+n [''unit exponent must be scalar'''
L2=. '(;:''',(>y),''');m,&<n'
(y)=: 2 :(L1;L2)
i.0 0
)
uni=:1 :0
:
'xu xv xx'=.x
'yu yv yx'=.y
zv=.xv u yv NB. basic operation
xb=.xu e.yu NB. find unit overlap
select. u`''
case. +`- do.
assert. xu -: yu ['units must match'
assert. xx -: yx ['unit exponents must match'
zu=. xu
zx=. xx
case. *`'' do.
zu=. ~.xu,yu
zx=. (xu,yu) +//. xx,yx
case. %`'' do.
zu=. ~.xu,yu
zx=. (xu,yu) -//. xx,yx
case. do. assert 0['unsuppported operation'
end.
(/:~zu);zv ,&< zx/:zu
)
dimensionless=:1 :0
'';m;i.0
)
raw=: 1 {:: ]
example use:
units 'm g s' NB. meters grams seconds
10 m 1 NB. 10 meters
10 m 1 *uni 10 s _1 NB. meters/second
10 m 1 *uni 10 s _1 * uni 10 s _1 NB. meters/second^2
10 m 1 *uni^:3 (1 dimensionless)
10 m 1 -uni 3 m 1
raw 10 m 1
I should probably also write a displayform verb, if I knew what
the display should look like.
FYI,
--
Raul
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