Another problem: ... is not a valid syntax.

val2 -> RGBColor[x2, y2, z2], ...

No error if it is removed

ShowCA[list_, opts__] := 
 Map[Show[
    Graphics[
     RasterArray[
      list[[#]] /. {val1 -> RGBColor[x1, y1, z1], 
        val2 -> RGBColor[x2, y2, z2]}]], opts] &, Range[Length[list]]]

Hi Hoa,

Seems like you are new to the Wolfram Language / Mathematica. The code you shared just defines a function named ShowCA. You have to evaluate an expression involving the function and its arguments. Simple example

Define a function named myFunction that takes a single argument and evaluates to it's square.

myFunction[arg_] := arg^2

Evaluate

myFunction[4]
(* 16 *)

I don't have the book you are referring to but I am guessing it is trying to do something like this

ClearAll@animateCA;
animateCA[rule_Integer, steps_Integer, 
  colorRules : List[__Rule] : {0 -> LightBlue, 1 -> Red}] :=
  Animate[
  ArrayPlot[
   ArrayPad[CellularAutomaton[rule, {{1}, 0}, {n, All}],
    {{0, steps - n}, {steps - n, steps - n}}],
   ColorRules -> colorRules],
  {n, 0, steps, 1}]

Then you can evaluate

animateCA[30, 75]

Different rule and colors

animateCA[73, 75, {0 -> LightGreen, 1 -> Magenta}]

Note: I adapted the code from this answer on MSE.

Thank you for taking your time responding to my message. I appreciate you. Re-run. It stated the same. Book was published 1996, old codes perhaps.

ShowCA[list_, opts__] :=
 Map[Show[Graphics[RasterArray[ list[ [#] ] /.
       {val1 -> RGBColor[x1, y1, z1], 
        val2 -> RGBColor[x2, y2, z2], ...}]], opts] &, 
  Range[Length[list]]   ]

Syntax::sntxf: "list[[#]]/." cannot be followed by "{val1->RGBColor[x1,y1,z1],val2->RGBColor[x2,y2,z2],...}".

Hello Rohit Namjoshi and thanks again.

From Richard J. Gaylord (the author) and that was it.

We can create a "flip-card" animation of the evolution of a CA using the following command:

ShowCA[list_, opts_] ::
Map[Show[Graphics[RasterArray[list[[#]] /.
{vall -> RGBColor[xl, yl, zl],
val2 -> RGBColor[x2, y2, z2], ... }]], opts]&, Range[Length[list]]]