eval_unary

eval_unary   f   x

Evaluates f x. f can also be an operator.

Source code:

    if { [regexp \[a-z\] $f match] } {
	# Seems that "f" is a function (because the name contains letters).
	eval "$f {$x}"
    } else {
	# Seems that "f" is something like "1+" or "42==".
	expr $f $x
    }