How to define part of a Manipulate control variable definition to reduce code duplication

Question

This is a little related to this question

Define control as variable in Mathematica

But the above question did not answer my problem, as it talks about the f

Answer 1

I was going to give a solution almost the same as Leonid's and use With to insert the code, but he beat me to it, so here's an alternative way. Define a dynamic local function using ControlType -> None that does your styling:

Manipulate[Plot[{f, g + 1}, {x, -1, 1}], 
 Dynamic[Grid[{{Style["f(x)="], pu[f]}, 
       {Style["g(x)="], pu[g]}}]], 
{{pu, Function[{f}, PopupMenu[Dynamic[f], {x, x^2, x^3}, ImageSize -> Tiny], 
        HoldFirst]}, None}]

By the way, the Style[] in Style["f(x)="] is redundant, as you are not actually setting any styles...

Answer 2

What about this

Manipulate[Plot[f*g, {x, -1, 1}],
 Evaluate@
  With[{styleAndpopup = 
      Function[{st, fun}, 
         {
           Style[st], 
           PopupMenu[Dynamic[fun], {x, x^2, x^3}, ImageSize -> Tiny]
         }, 
         HoldAll]},
    Grid[{styleAndpopup["f(x)=", f], styleAndpopup["g(x)=", g]}]]]

This is actually a tiny example of the code-generation at work, since if you look at the FullForm of the resulting Manipulate, you will see the same expression you originally started with. The styleAndpopup is actually not a function here, but a macro, locally defined using With.

EDIT

Per request of the OP - generalizing to many controls. The easiest fix is to insert Sequence@@... as Sequence @@ {First@control1[.... However, there is some extraneous stuff that can be removed as well:

Manipulate[{x, y}, 
 Evaluate@With[{control1 = 
     Function[{var, initialValue, str, from, to, incr}, 
       Unevaluated@{{var, initialValue, str}, from, to, incr, ImageSize -> Tiny}, 
       HoldAll]}, 
   Sequence @@ {
     control1[x, 0, "x=", 0, 1, .1], 
     control1[y, 0, "y=", 0, 2, .1], 
     control1[z, 0, "z=", 0, 10, .1]}]]

Answer 3

One could do this:

Manipulate[
  Plot[f*g, {x, -1, 1}]
, Grid[
    { {Style["f(x)="], PopupMenu[Dynamic[f], opts]}
    , {Style["g(x)="], PopupMenu[Dynamic[g], opts]}
    }
  ]
] /. opts -> Sequence[{x, x^2, x^3}, ImageSize -> Tiny]

If one is in the habit of assigning down-values to symbols whose names do not begin with $, then it would be prudent to wrap the whole thing in Block[{x, opts}, ...] in case x and opts have globally-defined values.

A similar technique is possible for the case of multiple controls:

Manipulate[
  {x, y, z}
, Grid[
    { {control1[x, 0, "x=", 0, 1, .1]}
    , {control1[y, 0, "y=", 0, 2, .1]}
    , {control1[z, 0, "z=", 0, 10, .1]}
    }
  ]
] /. control1[var_, initialValue_, str_, from_, to_, incr_] :>
       Control[{{var, initialValue, str}, from, to, incr, ImageSize -> Tiny}]