if ( expression ) ( command ) [ ( command ) ... ( command ) ]
Anything which can be evaluated. Commonly, this might be something like defined "isovar" , which is true if isovar is a command, function, or alias.
Any valid MeshTV command, or sequence of commands if you use the progn command
The if command takes an expression and a command to evaluate if the condition is true. Additional commands are evaluated if the expression is false. This is used when you are programming your own aliases.
if (defined "isovar") (plot isovar) (plot d)
if (defined "isovar") (progn (delete iso1) (plot isovar))
# The following example is read from an init file.