Modified code from the help file on $Pre:
$PreRead =.
SetAttributes[saveinputs, HoldAll];
inputs = {};
saveinputs[new_] := (inputs = {inputs, HoldForm[new]}; new);
$PreRead$PreRead =.
SetAttributes[saveinputs, HoldAll];
inputs = {};
saveinputs[new_] := (inputs = {inputs, HoldForm[new]}; new);
$PreRead = saveinputs;
Evaluating:
<>
then
Flatten[inputs]
{<>,8.,RowBox[{Flatten,[,inputs,]}]}
If you look at the Cell Expression for the 8. it is actually a TagBox
TagBox["8.`", HoldForm]
Why does a syntax error cause this?
Example where this causes a problem in code:
$PreRead =.
SetAttributes[saveinputs, HoldAll];
inputs = {};
saveinputs[new_] := (inputs = {inputs, HoldForm[new]};
If[Unevaluated[new],
new,
new);
$PreRead$PreRead =.
SetAttributes[saveinputs, HoldAll];
inputs = {};
saveinputs[new_] := (inputs = {inputs, HoldForm[new]};
If[Unevaluated[new],
new,
new);
$PreRead = saveinputs;
When evaluating pretty much anything you get:
ToExpression::esntx: Could not parse 8.` as Mathematica input.
If the test clause of the if statement in the above code does not depend on new then it runs fine.
$PreRead =.
SetAttributes[saveinputs, HoldAll];
inputs = {};
saveinputs[new_] := (inputs = {inputs, HoldForm[new]};
If[True,
new,
new);
$PreRead$PreRead =.
SetAttributes[saveinputs, HoldAll];
inputs = {};
saveinputs[new_] := (inputs = {inputs, HoldForm[new]};
If[True,
new,
new);
$PreRead = saveinputs;
The above works fine.
How am I changing new in the test clause to cause this to fail?
