In the source code for the CDF demonstration on Fractal Curves, Roman Maeder uses a statement tt=Fixup[t]. Mathematica accepts this statement but I cannot find any documentation on the ?Function? The source is as follows:
SetAttributes[Curve, Flat]
Curve /: r_c _Curve := r # & /@ c
simplify[c_Curve] :=
c //. {Curve[Turn[r1_], Turn[r2_]] :> Curve[Turn[r1 + r2]],
Curve[Turn[[Angle]_ /; [Angle] == 0.0]] :> Curve[]}
Iterate[c_Curve, template_Curve] := c /. Move[l_] :> l template
Iterate[c_Curve, template : {__Curve}] :=
c /. Move[l_, n_: 1] :> l template[[n]]
Move /: l_Move[l1, args___] := Move[l l1, args]
Turn /: l_Turn[a_] := Turn[a]
Fractal[c_Curve, t_, n_Integer ?NonNegative] :=
With[{tt = Fixup[t]}, Nest[Iterate[#, tt] &, c, n]]
Manipulate[examples;
Graphics[Fractal[ex[[1]], ex[[2]], n],
ImageSize -> {450, 400}], {{n, 3, "iterations"}, 0, 5, 1,
Appearance -> "Labeled"}, {{ex, examples[[1]], "replacement curves",
ControlType -> SetterBar},
Thread[examples -> {Graphics[Fractal[#[[1]], #[[2]], 1],
ImageSize -> {70, 70}] & /@ examples}],
ControlType -> SetterBar}, SaveDefinitions -> True]
and I get an error in the Fractal function call that I am trying to understand.
The CDF runs fine.