Sarnold 2005-11-10 -- The purpose is to offer a simple let command that works very much like C assignements for basic computations. The goal is not to join the general thing, but rather to keep it simple for everyday work.
Here is how it works :
let varname assignment arg ...
When assignment equals the '=' string, behaves like 'set varname [expr arg ...]'.
When assignment is the '=' string following an operator like +, -, *, / or %,
it behaves like 'set varname [expr {$varname <operator> args}]' % let a = 10 10 % let a = $a - 1 9 % puts $a 9 % let a *= 2 18
Please note that arguments do not have to be distinct. You can write this:
let a = $a+2
or this:
let a = 3 * 4
and even:
let a = {$b*cos($d)}It is better to enclose expr-essions into braces when they contain variables.
Here it is :
proc let {varname assign args} {
upvar $varname leftvalue
if {[llength $args]==1} {
set args [lindex $args 0]
}
set args [uplevel expr $args]
switch -exact -- $assign {
+= {set leftvalue [expr {$leftvalue+$args}]}
-= {set leftvalue [expr {$leftvalue-$args}]}
*= {set leftvalue [expr {$leftvalue*$args}]}
/= {set leftvalue [expr {$leftvalue/$args}]}
%= {set leftvalue [expr {$leftvalue%$args}]}
= {set leftvalue $args}
default {error "invalid syntax : second argument is not an assignment"}
}
return $leftvalue
}See let.