@Override
public Node forSubscriptExpr(SubscriptExpr that) {
if (!Shell.getAssignmentPreDesugaring()) {
return super.forSubscriptExpr(that);
} else {
// Rewrite a subscript expression into a method call (pretty straightforward)
Expr obj = that.getObj();
List<Expr> subs = that.getSubs();
Option<Op> op = that.getOp();
List<StaticArg> staticArgs = that.getStaticArgs();
if (!op.isSome()) bug(that, "Subscript operator expected");
Op knownOp = op.unwrap();
Expr result =
ExprFactory.makeMethodInvocation(
that,
obj,
knownOp,
staticArgs,
ExprFactory.makeTupleExpr(NodeUtil.getSpan(knownOp), subs));
return (Expr) recur(result);
}
}
@Override
public Node forAssignment(Assignment that) {
// System.out.println("PreDesugar entry");
// Here there are three sorts of rewrite to consider:
// (a) If this is a compound assignment, rewrite to use ordinary assignment.
// (b) If the lhs is a tuple, rewrite into a set of individual assignments.
// (c) If the lhs is a subscript expression, rewrite to a method call.
List<Lhs> lhs = that.getLhs();
Option<FunctionalRef> assignOp = that.getAssignOp();
Expr rhs = that.getRhs();
List<CompoundAssignmentInfo> assignmentInfos = that.getAssignmentInfos();
if (!Shell.getAssignmentPreDesugaring()) {
// System.out.println("Did not PreDesugar");
return super.forAssignment(that);
} else if (assignOp.isSome() || lhs.size() > 1) {
// System.out.println("Compound/tuple PreDesugar");
// Compound and/or tuple assignment
// The basic idea is to transform `(a, b.field, c[sub1,sub2]) := e` into
// `do (ta, tb, tc, tsub1, tsub2, (t1, t2, t3)) = (a, b, c, sub1, sub2, e)
// a := t1; tb.field := t2; tc[tsub1, tsub2] := t3 end`
// (TODO) Unfortunately, currently we don't handle nested binding tuples.
// For now, we'll just transform it into
// `do (ta, tb, tc, tsub1, tsub2) = (a, b, c, sub1, sub2)
// (t1, t2, t3) = e
// a := t1; tb.field := t2; tc[tsub1, tsub2] := t3 end`
// which merely loses a bit of potential parallelism.
// We omit the first tuple binding if the tuple is empty.
// If it is a compound assignment `(a, b.field, c[sub1,sub2]) OP= e`, it becomes
// `do (ta, tb, tc, tsub1, tsub2) = (a, b, c, sub1, sub2)
// (t1, t2, t3) = (ta, tb, tc[tsub1, tsub2]) OP e
// a := t1; tb.field := t2; tc[tsub1, tsub2] := t3 end`
List<LValue> exprLValues = Useful.list();
List<LValue> otherLValues = Useful.list();
List<Expr> otherExprs = Useful.list();
List<Expr> assignments = Useful.list();
boolean isCompound = assignOp.isSome();
List<Expr> accesses = Useful.list();
Span thatSpan = NodeUtil.getSpan(that);
for (Lhs lh : lhs) {
Span lhSpan = NodeUtil.getSpan((Expr) lh);
Id tempId = DesugarerUtil.gensymId(lhSpan, "e");
VarRef tempVar = ExprFactory.makeVarRef(lhSpan, tempId);
exprLValues = Useful.snoc(exprLValues, NodeFactory.makeLValue(lhSpan, tempId));
if (lh instanceof SubscriptExpr) {
SubscriptExpr lhsub = (SubscriptExpr) lh;
Expr obj = lhsub.getObj();
Span objSpan = NodeUtil.getSpan(obj);
List<Expr> subs = lhsub.getSubs();
Id baseTempId = DesugarerUtil.gensymId(objSpan, "b");
VarRef baseTempVar = ExprFactory.makeVarRef(objSpan, baseTempId);
otherLValues = Useful.snoc(otherLValues, NodeFactory.makeLValue(objSpan, baseTempId));
otherExprs = Useful.snoc(otherExprs, obj);
List<Expr> subTempVars = Useful.list();
for (Expr sub : lhsub.getSubs()) {
Span subSpan = NodeUtil.getSpan(sub);
Id subTempId = DesugarerUtil.gensymId(subSpan, "s");
subTempVars = Useful.snoc(subTempVars, ExprFactory.makeVarRef(subSpan, subTempId));
otherLValues = Useful.snoc(otherLValues, NodeFactory.makeLValue(subSpan, subTempId));
}
otherExprs = Useful.concat(otherExprs, subs);
SubscriptExpr newLhs =
ExprFactory.makeSubscriptExpr(
NodeUtil.getSpan(lhsub),
baseTempVar,
subTempVars,
lhsub.getOp(),
lhsub.getStaticArgs());
if (isCompound) accesses = Useful.snoc(accesses, newLhs);
assignments =
Useful.snoc(assignments, ExprFactory.makeAssignment(thatSpan, newLhs, tempVar));
} else if (lh instanceof FieldRef) {
FieldRef lhref = (FieldRef) lh;
Expr obj = lhref.getObj();
Span objSpan = NodeUtil.getSpan(obj);
Id objTempId = DesugarerUtil.gensymId(objSpan, "o");
VarRef objTempVar = ExprFactory.makeVarRef(objSpan, objTempId);
otherLValues = Useful.snoc(otherLValues, NodeFactory.makeLValue(objSpan, objTempId));
otherExprs = Useful.snoc(otherExprs, obj);
FieldRef newLhs =
ExprFactory.makeFieldRef(NodeUtil.getSpan(lhref), objTempVar, lhref.getField());
if (isCompound) accesses = Useful.snoc(accesses, newLhs);
assignments =
Useful.snoc(assignments, ExprFactory.makeAssignment(thatSpan, newLhs, tempVar));
} else if (lh instanceof VarRef) {
VarRef lhvar = (VarRef) lh;
Span varSpan = NodeUtil.getSpan(lhvar);
Id varTempId = DesugarerUtil.gensymId(varSpan, "v");
VarRef varTempVar = ExprFactory.makeVarRef(varSpan, varTempId);
otherLValues = Useful.snoc(otherLValues, NodeFactory.makeLValue(varSpan, varTempId));
otherExprs = Useful.snoc(otherExprs, lhvar);
if (isCompound) accesses = Useful.snoc(accesses, varTempVar);
assignments =
Useful.snoc(assignments, ExprFactory.makeAssignment(thatSpan, lhvar, tempVar));
} else {
bug(that, "Malformed assignment LHS");
}
}
Expr result = ExprFactory.makeBlock(thatSpan, assignments);
if (otherExprs.size() > 0) {
Expr otherRhs = ExprFactory.makeMaybeTupleExpr(thatSpan, otherExprs);
result = ExprFactory.makeLocalVarDecl(thatSpan, otherLValues, otherRhs, result);
}
Expr newRhs =
isCompound
? ExprFactory.makeOpExpr(
NodeUtil.spanTwo(assignOp.unwrap(), rhs),
assignOp.unwrap(),
ExprFactory.makeMaybeTupleExpr(thatSpan, accesses),
rhs)
: rhs;
result = ExprFactory.makeLocalVarDecl(thatSpan, exprLValues, newRhs, result);
return (Expr) recur(result);
} else if (lhs.get(0) instanceof SubscriptExpr) {
// System.out.println("PreDesugar single subscript expr");
// Subscripted assignment
SubscriptExpr lhExpr = (SubscriptExpr) lhs.get(0);
Expr obj = lhExpr.getObj();
List<Expr> subs = lhExpr.getSubs();
Option<Op> op = lhExpr.getOp();
List<StaticArg> staticArgs = lhExpr.getStaticArgs();
if (!op.isSome()) bug(lhExpr, "Subscript operator expected");
Op knownOp = op.unwrap();
Expr result =
ExprFactory.makeMethodInvocation(
that,
obj,
NodeFactory.makeOp(knownOp, knownOp.getText() + ":="),
staticArgs,
ExprFactory.makeTupleExpr(NodeUtil.spanTwo(knownOp, rhs), Useful.cons(rhs, subs)));
return (Expr) recur(result);
} else {
// System.out.println("PreDesugar single expr of class " + lhs.get(0).getClass().getName());
return super.forAssignment(that);
}
}
