Forum OpenACS Q&A: Tcl curly braces
But that does not mean that the braces are superfluous. Using the curly braces avoids an extra trip throught the Tcl evaluator.
... and with the braces, "if" and "expr" can be byte-compiled and be much faster executed (sometimes an order of magnitude). In earlier versions of Tcl (before 8.0), the braces were indeed not needed, but now they are recommended. Unfortunately, there is still much code in 7.* fashion. If you are interested, here is a script that fixes many of such occurrences in current openacs: http://media.wu-wien.ac.at/download/normalize_expressions.tcl