if 0 {Richard Suchenwirth 2005-01-18 - Here's a little fun project that does "arithmetics" on chemical formulae (see example at bottom).}
proc chem args {
set mode +
set factor 1
foreach arg $args {
switch -regexp -- $arg {
[+] - [-] {set mode $arg; set factor 1}
^[0-9]+$ {set factor $arg}
default {
foreach e [chem'split $arg] {
inc a($e) [expr {$mode eq "-"?"-":""}]$factor
}
}
}
}
set res ""
foreach e [array names a] {
if {$a($e)>0} {append res $e}
if {$a($e)>1} {append res $a($e)}
}
set res
}if 0 {This splits a compound into its atoms, e.g.
% chem'split H2SO4 H H S O O O O
}
proc chem'split compound {
set res {}
foreach {- el n} [regexp -all -inline {([A-Z][a-z]?)([0-9]*)} $compound] {
if {$n eq ""} {set n 1}
for {set i 0} {$i<$n} {incr i} {lappend res $el}
}
set res
}#-- A generic incrementor that creates a variable if it doesn't exist:
proc inc {varName {amount 1}} {
upvar 1 $varName var
if ![info exists var] {set var 0}
incr var $amount
}if 0 {Testing - still wrong (what are the rules of ordering elements in compounds?), but the element sum is right at least:
% chem NaOH + HCl - H2O ClNa
Tcling chemists, take it with a grain of salt - and please contribute to this page ! :^)
DKF: Rules for ionic substances are that you start from most electropositive ion and go to most electronegative ion. I think. ;^)