Editing Conditional (computer programming) (section)

====Tcl====
{{Main|Tcl}}
In [[Tcl]] <code>if</code> is not a keyword but a function (in Tcl known as command or <code>proc</code>). For example
<syntaxhighlight lang="tcl">
if {$x > 10} {
   puts "Foo!"
}
</syntaxhighlight>
invokes a function named <code>if</code> passing 2 arguments: The first one being the condition and the second one being the true branch. Both arguments are passed as strings (in Tcl everything within curly brackets is a string).

In the above example the condition is not evaluated before calling the function. Instead, the implementation of the <code>if</code> function receives the condition as a string value and is responsible to evaluate this string as an expression in the callers scope.<ref>{{cite web|title=New Control Structures|url=https://wiki.tcl-lang.org/page/New+Control+Structures|publisher=[[Tcler's wiki]]|access-date=August 21, 2020}}</ref>

Such a behavior is possible by using <code>uplevel</code> and <code>expr</code> commands:
:Uplevel makes it possible to implement new control constructs as Tcl procedures (for example, uplevel could be used to implement the while construct as a Tcl procedure).<ref>{{cite web|title=uplevel manual page|url=https://www.tcl.tk/man/tcl8.6/TclCmd/uplevel.htm|publisher=[[www.tcl.tk]]|access-date=August 21, 2020}}</ref>

Because <code>if</code> is actually a function it also returns a value:
:The return value from the command is the result of the body script that was executed, or an empty string if none of the expressions was non-zero and there was no bodyN.<ref>{{cite web|title=if manual page|url=http://www.tcl.tk/man/tcl8.6/TclCmd/if.htm|publisher=[[www.tcl.tk]]|access-date=August 21, 2020}}</ref>