unit attribute to list elements

Lines <- "cel 3.0 m/s

Constants.DF <- read.table(textConnection(Lines), as.is = TRUE)
Constants <- as.list(Constants.DF[[2]])
names(Constants) <- Constants.DF[[1]]
for(i in seq_along(Constants)) comment(Constants[[i]]) <- Constants.DF[i, 3]

# get value
Constants$Z0

# get comment
comment(Constants$Z0)

# add another Constant
Constants$e <- 2.7
comment(Constants$e) <- "exp"

Hi,

I've started my own (first) package, part of which consists in
listing common physical constants (Planck's constant, the speed of
light in vacuum, etc). I'm wondering what would be a good way of
dealing with pairs of value/unit.

constants <- list( cel = 2.99792458e8 , #m/s
Z0 = 376.730313461, #ohm
eps0 = 8.854187817e-12,#F/m
mu0 = 4*pi*1e-7,#N/A^2
G = 6.67428e-11 # m^3 kg-1 s-2
)

I thought I could include the unit in the names attribute of each
element, as in :

names(constants$cel)<- " speed of light in vacuum [m.s^-1]"

Writing this for every element is very redundant... Is there any way
to access and set the name of each first level element of the list?

namesFirstLevelElements(constants)<- c(" speed of light in vacuum
[m.s^-1]",
"impedance of vacuum [some unit]",
...)

Quite possibly, I'm completely on the wring track;

- maybe such a package already exists

- a custom class or structure would be more appropriate? I don't
really know how to deal with classes, though, and I'd like to keep
the access to the constants' values as direct and generic as possible.

Many thanks in advance,

baptiste