• $Pre is a global variable whose value, if set, is applied to every input expression.
• Unless $Pre
is assigned to be a function which holds its arguments unevaluated, input expressions will be evaluated before $Pre
is applied, so the effect of $Pre
will be the same as $Post
is applied to expressions, while $PreRead
is applied to strings which have not yet been parsed into expressions.
• New in Version 1.