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
}
}
}
}
chem'Hill [array get a]
}
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
}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. ;^)
TS: If computer generated it's best to use Hill order
RS: Thanks for the hint! Here's my Tcl implementation of Hill order:
proc chem'Hill chemdict {
array set arr $chemdict
set res ""
if {[info exists arr(C)] && $arr(C)>0} {
append res C [expr {$arr(C)>1? "$arr(C)":""}]
unset arr(C)
if {[info exists arr(H)] && $arr(H)>0} {
append res H [expr {$arr(H)>1? "$arr(H)":""}]
unset arr(H)
}
}
foreach elem [lsort [array names arr]] {
if {$arr($elem)>0} {
append res $elem [expr {$arr($elem)>1? "$arr($elem)":""}]
}
}
set res
}Testing (samples from the link above):
% chem'Hill {Al 6 Ca 5 O 14}
Al6Ca5O14
% chem'Hill {Na 1 H 1 C 1 O 3}
CHNaO3
% chem'Hill {Se 2 S 2 N 2 H 2 C 4}
C4H2N2S2Se2