> So you can have 1000mm or 0.001km but not 1m?
If the scale factor is optional, then numbers like 1m are problematic because
the m can represent either milli or meter. This is resolved by requiring the
scale factor and defining a unity scale factor. I propose '_'. So 1m represents
milli and 1_m represents 1 meter.
> If units are retained, what you have is no longer a simple number, but
> a value with a unit, and is a quite different beast. (For instance,
> addition would have to cope with unit mismatches (probably by throwing
> an error), and multiplication would have to combine the units (length
> * length = area).) That would be a huge new feature.
Indeed. I am not proposing that anything be done with the units other than
possibly retain them for later output. Doing dimensional analysis on
expressions
would be a huge burden both for those implementing the language and for those
using them in a program. Just allowing the units to be present, even it not
retained, is a big advantage because it can bring a great deal of clarity to
the
meaning of the number. For example, even if the language does not flag an error
when a user writes:
vdiff = 1mV - 30uA
the person that wrote the line will generally see it as a problem and fix it.
In my experience, providing units is the most efficient form of documentation
available in numerical programming in the sense that one or two additional
characters can often clarify otherwise very confusing code.
My feeling is that retaining the units on real literals is of little value if
you don't also extend the real variable type to hold units, or to create
another
variable type that would carry the units. Extending reals does not seem like
a good idea, but creating a new type, quantity, seems practical. In this case,
the units would be rather ephemeral in that they would not survive any
operation. Thus, the result of an operation between a quantity and either
a integer, real or quantity would always be a real, meaning that the units are
lost. In this way, units are very light-weight and only really serve as
documentation (for both programmers and end users).
But this idea of retaining the units is the least important aspect of this
proposal. The important aspects are:
1. It allows numbers to be entered in a clean form that is easy to type and
easy
to interpret
2. It allows numbers to be output in a clean form that is easy to interpret.
3. In many cases it allows units to be inserted into the code in a very natural
and clean way to improve the clarity of the code.
> Question, though: What happens with exa-? Currently, if the parser
> sees "1E", it'll expect to see another number, eg 1E+1 == 10.0. Will
> this double meaning cause confusion?
Oh, I did not see this. Both SPICE and Verilog limit the scale factors to the
common ones (T, G, M, k, _, m, u, n, p, f, a). I work in electrical
engineering,
and in that domain exa never comes up. My suggestion would be to limit
ourselves
to the common scale factors as most people know them. Using P, E, Z, Y, z, and
y often actually works against us as most people are not familiar with them and
so cannot interpret them easily.
-Ken
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