invalid bareword in expression

[heinrichmartin]

Hi,
out of curiosity: is there a reason for not accepting barewords as strings in expressions (expr/if).

background:
I know of [apply] and [list] to dynamically create commands, but in my particular use case I use the following pattern to inject a constant:

proc dynproc args [format {
# dynamically created proc body
...
if {%s eq ...} ... ;# does not always produce correct syntax
if {[::tcl::mathop::eq %s ...]} ... ;# 10% slower
...
} [list $const]]

Using (the string representation of a) [list] guaranties that the body has correct syntax in commands, but not in expressions. That's why I wonder whether there is a specific reason for this.

Regards
Martin

[Arjen Markus]

I am not sure if there is a specific reason, but it is part of the general improvement of the [expr] command and related aspects of Tcl - see the various TIPs.

But what about: if {{%s} eq ...}

If you use the extra braces, the substituted string is acceptable and not a bare word. Unless you want to substitute %s by $variable ...

Regards,

Arjen

[heinrichmartin]

On Friday, May 4, 2018 at 10:53:31 AM UTC+2, Arjen Markus wrote:
> But what about: if {{%s} eq ...}

I was thinking so, too, but it is not a general solution. This would work only if the canonical string representation of a list always uses backslash escapes.

A simple counterexample is [format {if {{%s} eq ...} ...} [list " "]]. Same for "%s"; and building the full expression with list is not a solution either.

[briang]

The reason is that the [expr] language is not Tcl, it is it's own language. Different syntax, different semantics.

-Brian