Richard Suchenwirth - Tcl is somehow more than just a programming language. At times it feels like a quite powerful operating system, with commands that have their own "small languages" (sed, awk in Unix; expr, regexp... in Tcl). But while implementing seds or awks functionality in C is hard work, in Tcl the creation of a custom "small language" is made easy by strong string processing commands. Hence I chose a small math language for my New Year's Eve fun project.
The accepted language is based on expr's, which is well known to Tcl'ers and able to express all C arithmetics (and more), so isn't exactly small. However, I added some functionalities discussed earlier on the comp.lang.tcl newsgroup, plus some sugar to make it look more similar to conventional math notation:
These effects took little effort, as they were reached by string manipulations on the arguments to math, which transform them to valid expr language, and evaluate that in caller's scope. On the other hand, no tokenization like that of expr was done (where $i+$j is equivalent to $i + $j), so the arguments have to be list elements separated by whitespace. At the place marked "more preprocessing here", you can add your own ideas. See the usage examples at end, and enjoy!
proc math args {
if {[llength $args]==1} {set args [lindex $args 0]}
foreach mathcmd [split $args ";"] {
set cmd ""
if {[lindex $mathcmd 1]=="="} {
set cmd [list set [lindex $mathcmd 0]]
set expr [lrange $mathcmd 2 end]
} else {set expr $mathcmd}
set expr2 "expr \{("
set previous ""
foreach i $expr {
if [uplevel 1 info exists $i] {set i \$$i}
if [regexp -- {--+} $i] {set i )/double(}
if [isBuiltin $previous] {set i ($i)}
if {[isNumeric $previous] && [regexp {^[$A-Za-z�_]} $i]} {
set i *$i
}
# more preprocessing here..
set previous $i
append expr2 $i
}
append expr2 ")\}"
if {$cmd==""} {
set cmd $expr2
} else {
append cmd " \[$expr2\]"
}
set res [uplevel 1 $cmd]
}
set res ;# return last expression's result
}
proc isBuiltin word {
expr [lsearch -exact {
abs cosh log sqrt
acos double log10 srand
asin exp pow tan
atan floor rand tanh
atan2 fmod round
ceil hypot sin
cos int sinh} $word ]>=0
}
proc isNumeric x {expr ![catch {expr $x*1}]}# testing, and usage examples:
math {
a = 1 * (2 - 1);
b = sqrt 4;
c = 3 a - b
-------
a + b
}
puts c:$c