Reference Guides » Undocumented Contexts

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Front End Programming

The Mathematica front-end is almost as complex as the Mathematica kernel, but much worse understood. There are a number of contexts which implement different functionality that it uses.

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FrontEnd

The "FrontEnd`" context supplies things like "front-end packets" which tell the front-end to do things.

There is a decent listing of these with usages here .

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FE

The "FE`" context provides utilities used by the front-end

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makePlainText

FE`makePlainText converts a front-end expression into plain text: 

 FE`makePlainText[NotebookRead[EvaluationCell[]]]

 "In[6]:= FE`makePlainText[NotebookRead[EvaluationCell[]]]"

It's basically like FrontEndExecute with ExportPacket and "PlainText" as described here .

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Evaluate

FE`Evaluate evaluates front-end expressions, basically. It'll usually imitate what you see when working with these things in the actual front-end. E.g.: 

 img =
    FE`Evaluate[
       (* imports an Image as a GraphicsBox *)

   FEPrivate`ImportImage@
          FrontEnd`FileName[{"Ribbons", "Common"}, "Close.png"]
       ];
img // ToExpression (* creates the proper image from the GraphicsBox *)

Compare to: 

 RawBoxes@DynamicBox@
  FEPrivate`ImportImage@
      FrontEnd`FileName[{"Ribbons", "Common"}, "Close.png"]
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FEPrivate

The "FEPrivate`" context supplies a mini-language that the front-end understands. Here are some of it's useful structures.

The language itself is much more rigid and inflexible, given that it's closer to a DSL than a standard language. 

 Select[
StringSplit[Names["FEPrivate`*"], "`"][[All, -1]],
NameQ
]

 {"And","EmitSound","FrontEndExecute","FrontEndResource","FrontEndResourceString","Greater","Head","If","Less","MemberQ","Not","Or","Part","SameQ","Set","SetDelayed","Switch","UnsameQ","Which","$ActivationKey","$OperatingSystem","$SystemID"}
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If / Switch / Which / And / Or / Not / MemberQ / SameQ / Head / Greater / Less / Part / Apply / Etc.

These are basically the same as in the kernel, but obviously do not evaluate unless called via FE`Evaluate on in the front-end itself. One thing to note is that many constructs are less powerful than in the kernel, so stick to simple things when possible.

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Set / SetDelayed

These are used to represent Set and SetDelayed , as one would expect, but they're almost always used with FrontEnd`SetValue as a wrapper, e.g.: 

 MathLink`CallFrontEndHeld[FrontEnd`SetValue@FEPrivate`Set[myVar, 2]]

Now the FE remembers that and we can get that value back from it later, maybe in a DynamicBox : 

 RawBoxes@DynamicBox[myVar]
413frontend-732377038742225435

Note that myVar still has no value: 

 myVar

 myVar

And if we change that value of myVar in the FE the Dynamic value will also update: 

 MathLink`CallFrontEndHeld[FrontEnd`SetValue@FEPrivate`Set[myVar, 5]] 
(* now the prior DynamicBox will read 5 *)

This can be useful as a way to set state. We can also use slightly more complicated patterns like: 

 MathLink`CallFrontEnd@
  FrontEnd`SetValue@FEPrivate`Set[cache[EvaluationNotebook[]], 5]

And pull this with: 

 MathLink`CallFrontEnd@
  FrontEnd`Value@cache[EvaluationNotebook[]]

 5

Note, though, that this type of thing can't be used with DynamicBox , though 

 RawBoxes@DynamicBox[cache[EvaluationNotebook[]]]

The most common use of Set and SetDelayed , though, is in the CurrentValue mechanism. The way CurrentValue updates is through FEPrivate`Set and FEPrivate`SetDelayed .

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See Also: