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@lshifr lshifr/FrozenCode.m
Created May 19, 2016

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A non-standard evaluator for Mathematica code, allowing to evaluate the code in the "frozen" mode
BeginPackage["FrozenCode`"]
FrozenCodeEvaluate::usage = "FrozenCodeEvaluate[Hold[code], {heads}] evaluates the code
in the 'frozen' mode, where only specific heads are allowed to evaluate";
Begin["`Private`"]
ClearAll[symbolToHideQ]
SetAttributes[symbolToHideQ, HoldFirst];
symbolToHideQ[s_Symbol, expandedSymbs_] :=! MemberQ[expandedSymbs, Unevaluated[s]];
ClearAll[globalProperties]
globalProperties[] := {DownValues, SubValues, UpValues (*,OwnValues*)};
ClearAll[getSymbolsToHide];
Options[getSymbolsToHide] = {
"Exceptions" -> {List, Hold, HoldComplete,
HoldForm, HoldPattern, Blank, BlankSequence, BlankNullSequence,
Optional, Repeated, Verbatim, Pattern, RuleDelayed, Rule, True,
False, Integer, Real, Complex, Alternatives, String,
PatternTest,(*Note- this one is dangerous since it opens a hole
to evaluation leaks. But too good to be ingored *)
Condition, PatternSequence, Except
}
};
getSymbolsToHide[code_Hold, headsToExpand : {___Symbol}, opts : OptionsPattern[]] :=
Join @@ Complement[
Cases[{
Flatten[Outer[Compose, globalProperties[], headsToExpand]], code},
s_Symbol /; symbolToHideQ[s, headsToExpand] :> Hold[s],
Infinity,
Heads -> True
],
Hold /@ OptionValue["Exceptions"]];
ClearAll[makeHidingSymbol]
SetAttributes[makeHidingSymbol, HoldAll];
makeHidingSymbol[s_Symbol] :=
Unique[hidingSymbol(*Unevaluated[s]*) (*,Attributes[s]*)];
ClearAll[makeHidingRules]
makeHidingRules[symbs : Hold[__Symbol]] :=
Thread[List @@ Map[HoldPattern, symbs] -> List @@ Map[makeHidingSymbol, symbs]];
ClearAll[reverseHidingRules];
reverseHidingRules[rules : {(_Rule | _RuleDelayed) ..}] :=
rules /. (Rule | RuleDelayed)[Verbatim[HoldPattern][lhs_], rhs_] :> (rhs :> lhs);
FrozenCodeEvaluate[code_Hold, headsToEvaluate : {___Symbol}] :=
Module[{symbolsToHide, hidingRules, revHidingRules, result},
symbolsToHide = getSymbolsToHide[code, headsToEvaluate];
hidingRules = makeHidingRules[symbolsToHide];
revHidingRules = reverseHidingRules[hidingRules];
result =
Hold[Evaluate[ReleaseHold[code /. hidingRules]]] /. revHidingRules;
Apply[Remove, revHidingRules[[All, 1]]];
result];
End[]
EndPackage[]
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