/// <summary> /// Performs lambda lifting (see <see cref="LambdaHelper.ExpandLambdas"/>) by replacing with bound variables /// maximally large subexpressions of a lambda that do not contain any of the lambda's bound variables. /// </summary> /// <param name="lambda">A lambda expression /// <code>(lambda x1: T1 ... x_n: T_n :: t)</code> /// where <c>t</c> contains the subexpressions <c>e1</c>, ..., <c>e_m</c>. These are maximally large /// subexpressions that do not contain the lambda's bound variables. /// </param> /// <returns> /// <list type="bullet"> /// <item> /// A function application <c>f(y1, ..., y_m)</c> where <c>f</c>'s body is defined to be the result of /// replacing the expressions <c>e1</c>, ..., <c>e_m</c> in <c>t</c> with bound variables /// <c>b1</c>, ..., <c>b_m</c>. /// </item> /// <item> /// Adds a definition and axiom for <c>f</c> to <see cref="lambdaFunctions"/> and <see cref="lambdaAxioms"/>. /// Memoizes <c>f</c> as the lifted lambda for <para>lambda</para>. /// </item> /// </list> /// </returns> private Expr LiftLambdaMaxHoles(LambdaExpr lambda) { // We start by getting rid of `old` expressions. Instead, we replace the free variables `x_i` that are // nested inside of `old` expressions with `old(x_i)` expressions. var oldFinder = new OldFinder(); oldFinder.Visit(lambda); var oldSubst = new Dictionary<Variable, Expr>(); foreach (var v in oldFinder.FreeOldVars) if (v is GlobalVariable g) { oldSubst.Add(g, new OldExpr(g.tok, new IdentifierExpr(g.tok, g)) {Type = g.TypedIdent.Type}); } var lambdaBody = Substituter.ApplyReplacingOldExprs( Substituter.SubstitutionFromDictionary(new Dictionary<Variable, Expr>()), Substituter.SubstitutionFromDictionary(oldSubst), lambda.Body); var lambdaAttrs = Substituter.ApplyReplacingOldExprs( Substituter.SubstitutionFromDictionary(new Dictionary<Variable, Expr>()), Substituter.SubstitutionFromDictionary(oldSubst), lambda.Attributes); var newLambda = new LambdaExpr(lambda.tok, lambda.TypeParameters, lambda.Dummies, lambdaAttrs, lambdaBody) { Type = lambda.Type }; // We perform lambda lifting on the resulting lambda which now contains only `old` expressions of the form // `old(x)` where `x` is a variable that is free in the lambda. return new MaxHolesLambdaLifter( newLambda, liftedLambdas, FreshLambdaFunctionName(), lambdaFunctions, lambdaAxioms) .VisitLambdaExpr(newLambda); }
/// <summary> /// Performs lambda lifting (see <see cref="LambdaHelper.ExpandLambdas"/>) by replacing the lambda's /// free variables with bound ones. /// </summary> /// <param name="lambda">A lambda expression /// <code>(lambda x1: T1 ... x_n: T_n :: t)</code> /// where <c>t</c> contains the free variables <c>y1</c>, ..., <c>y_m</c>. /// </param> /// <returns> /// <list type="bullet"> /// <item> /// A function application <c>f(y1, ..., y_m)</c> where <c>f</c>'s body is defined to be the result of /// replacing the free variables <c>y1</c>, ..., <c>y_m</c> in <c>t</c> with bound variables /// <c>b1</c>, ..., <c>b_m</c>. /// </item> /// <item> /// Adds a definition and axiom for <c>f</c> to <see cref="lambdaFunctions"/> and <see cref="lambdaAxioms"/>. /// Memoizes <c>f</c> as the lifted lambda for <para>lambda</para>. /// </item> /// </list> /// </returns> private Expr LiftLambdaFreeVars(LambdaExpr lambda) { // We start by getting rid of any use of "old" inside the lambda. This is done as follows. // For each variable "g" occurring inside lambda as "old(... g ...)", create a new name "og". // Replace each old occurrence of "g" with "og", removing the enclosing "old" wrappers. var oldFinder = new OldFinder(); oldFinder.Visit(lambda); var oldSubst = new Dictionary<Variable, Expr>(); // g -> g0 var callOldMapping = new Dictionary<Variable, Expr>(); // g0 -> old(g) foreach (var v in oldFinder.FreeOldVars) { var g = v as GlobalVariable; if (g != null) { var g0 = new GlobalVariable(g.tok, new TypedIdent(g.tok, g.TypedIdent.Name + "@old", g.TypedIdent.Type)); oldSubst.Add(g, new IdentifierExpr(g0.tok, g0)); callOldMapping.Add(g0, new OldExpr(g0.tok, new IdentifierExpr(g.tok, g))); } } var lambdaBody = Substituter.ApplyReplacingOldExprs( Substituter.SubstitutionFromDictionary(new Dictionary<Variable, Expr>()), Substituter.SubstitutionFromDictionary(oldSubst), lambda.Body); var lambdaAttrs = Substituter.ApplyReplacingOldExprs( Substituter.SubstitutionFromDictionary(new Dictionary<Variable, Expr>()), Substituter.SubstitutionFromDictionary(oldSubst), lambda.Attributes); if (0 < CommandLineOptions.Clo.VerifySnapshots && QKeyValue.FindStringAttribute(lambdaAttrs, "checksum") == null) { // Attach a dummy checksum to avoid issues in the dependency analysis. var checksumAttr = new QKeyValue(lambda.tok, "checksum", new List<object> {"lambda expression"}, null); if (lambdaAttrs == null) { lambdaAttrs = checksumAttr; } else { lambdaAttrs.AddLast(checksumAttr); } } // this is ugly, the output will depend on hashing order var subst = new Dictionary<Variable, Expr>(); var substFnAttrs = new Dictionary<Variable, Expr>(); var formals = new List<Variable>(); var callArgs = new List<Expr>(); var axCallArgs = new List<Expr>(); var dummies = new List<Variable>(lambda.Dummies); var freeTypeVars = new List<TypeVariable>(); var fnTypeVarActuals = new List<Type /*!*/>(); var freshTypeVars = new List<TypeVariable>(); // these are only used in the lambda@n function's definition // compute the free variables of the lambda expression, but with lambdaBody instead of lambda.Body Set freeVars = new Set(); BinderExpr.ComputeBinderFreeVariables(lambda.TypeParameters, lambda.Dummies, lambdaBody, null, lambdaAttrs, freeVars); foreach (object o in freeVars) { // 'o' is either a Variable or a TypeVariable. if (o is Variable) { var v = o as Variable; var ti = new TypedIdent(v.TypedIdent.tok, v.TypedIdent.Name, v.TypedIdent.Type); var f = new Formal(v.tok, ti, true); formals.Add(f); substFnAttrs.Add(v, new IdentifierExpr(f.tok, f)); var b = new BoundVariable(v.tok, ti); dummies.Add(b); if (callOldMapping.ContainsKey(v)) { callArgs.Add(callOldMapping[v]); } else { callArgs.Add(new IdentifierExpr(v.tok, v)); } Expr id = new IdentifierExpr(b.tok, b); subst.Add(v, id); axCallArgs.Add(id); } else { var tv = (TypeVariable) o; freeTypeVars.Add(tv); fnTypeVarActuals.Add(tv); freshTypeVars.Add(new TypeVariable(tv.tok, tv.Name)); } } var sw = new System.IO.StringWriter(); var wr = new TokenTextWriter(sw, true); lambda.Emit(wr); string lam_str = sw.ToString(); FunctionCall fcall; IToken tok = lambda.tok; Formal res = new Formal(tok, new TypedIdent(tok, TypedIdent.NoName, cce.NonNull(lambda.Type)), false); if (liftedLambdas.TryGetValue(lambda, out fcall)) { if (CommandLineOptions.Clo.TraceVerify) { Console.WriteLine("Old lambda: {0}", lam_str); } } else { if (CommandLineOptions.Clo.TraceVerify) { Console.WriteLine("New lambda: {0}", lam_str); } Function fn = new Function(tok, FreshLambdaFunctionName(), freshTypeVars, formals, res, "auto-generated lambda function", Substituter.Apply(Substituter.SubstitutionFromDictionary(substFnAttrs), lambdaAttrs)); fn.OriginalLambdaExprAsString = lam_str; fcall = new FunctionCall(new IdentifierExpr(tok, fn.Name)); fcall.Func = fn; // resolve here liftedLambdas[lambda] = fcall; List<Expr /*!*/> selectArgs = new List<Expr /*!*/>(); foreach (Variable /*!*/ v in lambda.Dummies) { Contract.Assert(v != null); selectArgs.Add(new IdentifierExpr(v.tok, v)); } NAryExpr axcall = new NAryExpr(tok, fcall, axCallArgs); axcall.Type = res.TypedIdent.Type; axcall.TypeParameters = SimpleTypeParamInstantiation.From(freeTypeVars, fnTypeVarActuals); NAryExpr select = Expr.Select(axcall, selectArgs); select.Type = lambdaBody.Type; List<Type /*!*/> selectTypeParamActuals = new List<Type /*!*/>(); List<TypeVariable> forallTypeVariables = new List<TypeVariable>(); foreach (TypeVariable /*!*/ tp in lambda.TypeParameters) { Contract.Assert(tp != null); selectTypeParamActuals.Add(tp); forallTypeVariables.Add(tp); } forallTypeVariables.AddRange(freeTypeVars); select.TypeParameters = SimpleTypeParamInstantiation.From(lambda.TypeParameters, selectTypeParamActuals); Expr bb = Substituter.Apply(Substituter.SubstitutionFromDictionary(subst), lambdaBody); NAryExpr body = Expr.Eq(select, bb); body.Type = Type.Bool; body.TypeParameters = SimpleTypeParamInstantiation.EMPTY; Trigger trig = new Trigger(select.tok, true, new List<Expr> {select}); lambdaFunctions.Add(fn); lambdaAxioms.Add(new ForallExpr(tok, forallTypeVariables, dummies, Substituter.Apply(Substituter.SubstitutionFromDictionary(subst), lambdaAttrs), trig, body)); } NAryExpr call = new NAryExpr(tok, fcall, callArgs); call.Type = res.TypedIdent.Type; call.TypeParameters = SimpleTypeParamInstantiation.From(freeTypeVars, fnTypeVarActuals); return call; }
public override Expr VisitLambdaExpr(LambdaExpr lambda) { var baseResult = base.VisitLambdaExpr(lambda); lambda = baseResult as LambdaExpr; if (lambda == null) { return baseResult; // apparently, the base visitor already turned the lambda into something else } // We start by getting rid of any use of "old" inside the lambda. This is done as follows. // For each variable "g" occurring inside lambda as "old(... g ...)", create a new name "og". // Replace each old occurrence of "g" with "og", removing the enclosing "old" wrappers. var oldFinder = new OldFinder(); oldFinder.Visit(lambda); var oldSubst = new Dictionary<Variable, Expr>(); // g -> g0 var callOldMapping = new Dictionary<Variable, Expr>(); // g0 -> old(g) foreach (var v in oldFinder.FreeOldVars) { var g = v as GlobalVariable; if (g != null) { var g0 = new GlobalVariable(g.tok, new TypedIdent(g.tok, g.TypedIdent.Name + "@old", g.TypedIdent.Type)); oldSubst.Add(g, new IdentifierExpr(g0.tok, g0)); callOldMapping.Add(g0, new OldExpr(g0.tok, new IdentifierExpr(g.tok, g))); } } var lambdaBody = Substituter.ApplyReplacingOldExprs( Substituter.SubstitutionFromHashtable(new Dictionary<Variable,Expr>()), Substituter.SubstitutionFromHashtable(oldSubst), lambda.Body); var lambdaAttrs = Substituter.ApplyReplacingOldExprs( Substituter.SubstitutionFromHashtable(new Dictionary<Variable, Expr>()), Substituter.SubstitutionFromHashtable(oldSubst), lambda.Attributes); if (0 < CommandLineOptions.Clo.VerifySnapshots && QKeyValue.FindStringAttribute(lambdaAttrs, "checksum") == null) { // Attach a dummy checksum to avoid issues in the dependency analysis. var checksumAttr = new QKeyValue(lambda.tok, "checksum", new List<object> { "lambda expression" }, null); if (lambdaAttrs == null) { lambdaAttrs = checksumAttr; } else { lambdaAttrs.AddLast(checksumAttr); } } // this is ugly, the output will depend on hashing order var subst = new Dictionary<Variable, Expr>(); var substFnAttrs = new Dictionary<Variable, Expr>(); var formals = new List<Variable>(); var callArgs = new List<Expr>(); var axCallArgs = new List<Expr>(); var dummies = new List<Variable>(lambda.Dummies); var freeTypeVars = new List<TypeVariable>(); var fnTypeVarActuals = new List<Type/*!*/>(); var freshTypeVars = new List<TypeVariable>(); // these are only used in the lambda@n function's definition // compute the free variables of the lambda expression, but with lambdaBody instead of lambda.Body Set freeVars = new Set(); BinderExpr.ComputeBinderFreeVariables(lambda.TypeParameters, lambda.Dummies, lambdaBody, lambdaAttrs, freeVars); foreach (object o in freeVars) { // 'o' is either a Variable or a TypeVariable. if (o is Variable) { var v = o as Variable; var ti = new TypedIdent(v.TypedIdent.tok, v.TypedIdent.Name, v.TypedIdent.Type); var f = new Formal(v.tok, ti, true); formals.Add(f); substFnAttrs.Add(v, new IdentifierExpr(f.tok, f)); var b = new BoundVariable(v.tok, ti); dummies.Add(b); if (callOldMapping.ContainsKey(v)) { callArgs.Add(callOldMapping[v]); } else { callArgs.Add(new IdentifierExpr(v.tok, v)); } Expr id = new IdentifierExpr(b.tok, b); subst.Add(v, id); axCallArgs.Add(id); } else { var tv = (TypeVariable)o; freeTypeVars.Add(tv); fnTypeVarActuals.Add(tv); freshTypeVars.Add(new TypeVariable(tv.tok, tv.Name)); } } var sw = new System.IO.StringWriter(); var wr = new TokenTextWriter(sw, true); lambda.Emit(wr); string lam_str = sw.ToString(); FunctionCall fcall; IToken tok = lambda.tok; Formal res = new Formal(tok, new TypedIdent(tok, TypedIdent.NoName, cce.NonNull(lambda.Type)), false); if (liftedLambdas.TryGetValue(lambda, out fcall)) { if (CommandLineOptions.Clo.TraceVerify) { Console.WriteLine("Old lambda: {0}", lam_str); } } else { if (CommandLineOptions.Clo.TraceVerify) { Console.WriteLine("New lambda: {0}", lam_str); } Function fn = new Function(tok, FreshLambdaFunctionName(), freshTypeVars, formals, res, "auto-generated lambda function", Substituter.Apply(Substituter.SubstitutionFromHashtable(substFnAttrs), lambdaAttrs)); fn.OriginalLambdaExprAsString = lam_str; fcall = new FunctionCall(new IdentifierExpr(tok, fn.Name)); fcall.Func = fn; // resolve here liftedLambdas[lambda] = fcall; List<Expr/*!*/> selectArgs = new List<Expr/*!*/>(); foreach (Variable/*!*/ v in lambda.Dummies) { Contract.Assert(v != null); selectArgs.Add(new IdentifierExpr(v.tok, v)); } NAryExpr axcall = new NAryExpr(tok, fcall, axCallArgs); axcall.Type = res.TypedIdent.Type; axcall.TypeParameters = SimpleTypeParamInstantiation.From(freeTypeVars, fnTypeVarActuals); NAryExpr select = Expr.Select(axcall, selectArgs); select.Type = lambdaBody.Type; List<Type/*!*/> selectTypeParamActuals = new List<Type/*!*/>(); List<TypeVariable> forallTypeVariables = new List<TypeVariable>(); foreach (TypeVariable/*!*/ tp in lambda.TypeParameters) { Contract.Assert(tp != null); selectTypeParamActuals.Add(tp); forallTypeVariables.Add(tp); } forallTypeVariables.AddRange(freeTypeVars); select.TypeParameters = SimpleTypeParamInstantiation.From(lambda.TypeParameters, selectTypeParamActuals); Expr bb = Substituter.Apply(Substituter.SubstitutionFromHashtable(subst), lambdaBody); NAryExpr body = Expr.Eq(select, bb); body.Type = Type.Bool; body.TypeParameters = SimpleTypeParamInstantiation.EMPTY; Trigger trig = new Trigger(select.tok, true, new List<Expr> { select }); lambdaFunctions.Add(fn); lambdaAxioms.Add(new ForallExpr(tok, forallTypeVariables, dummies, Substituter.Apply(Substituter.SubstitutionFromHashtable(subst), lambdaAttrs), trig, body)); } NAryExpr call = new NAryExpr(tok, fcall, callArgs); call.Type = res.TypedIdent.Type; call.TypeParameters = SimpleTypeParamInstantiation.From(freeTypeVars, fnTypeVarActuals); return call; }