I'm learning Tcl/Tk and am confused on the usage of curly braces in tcl.
To me it seems to be used to both indicate scope and declare strings! Is this a bug (or feature)?
Is my interpretation correct?
Answer
In a nutshell,
- Tcl's braces act like sh's single quotes -- group words (and lines) without interpolation.
- Tcl's double quotes act like sh's double quotes -- allowing interpolation.
The fact that you use curly braces in a proc definition is not mandatory. It's just the most convenient way to pass a script as an argument to proc without interpolating.
These are equivalent
proc add3 {a b c} {
return [expr {$a + $b + $c}]
}
and
proc add3_weird [list a b c] "return \[expr {\[set a] + \[set b] + \[set c]}]"
Once you internalize Tcl quoting, you'll realize how truly flexible Tcl can be.