// This is a compound comparison operator like: a < b < c.
// That's represented as binary operators, but it's not the same as (a<b) < c, so we do special transformations.
// We need to:
// - return true iff (a<b) && (b<c), but ensure that b is only evaluated once.
// - ensure evaluation order is correct (a,b,c)
// - don't evaluate c if a<b is false.
private MSAst.Expression FinishCompare(MSAst.Expression left)
{
Debug.Assert(_right is BinaryExpression);
BinaryExpression bright = (BinaryExpression)_right;
// Transform the left child of my right child (the next node in sequence)
MSAst.Expression rleft = bright.Left;
// Store it in the temp
MSAst.ParameterExpression temp = Ast.Parameter(typeof(object), "chained_comparison");
// Create binary operation: left <_op> (temp = rleft)
MSAst.Expression comparison = MakeBinaryOperation(
_op,
left,
Ast.Assign(temp, AstUtils.Convert(rleft, temp.Type)),
Span
);
MSAst.Expression rright;
// Transform rright, comparing to temp
if (IsComparison(bright._right))
{
rright = bright.FinishCompare(temp);
}
else
{
MSAst.Expression transformedRight = bright.Right;
rright = MakeBinaryOperation(
bright.Operator,
temp,
transformedRight,
bright.Span
);
}
// return (left (op) (temp = rleft)) and (rright)
MSAst.ParameterExpression tmp;
MSAst.Expression res = AstUtils.CoalesceTrue(
comparison,
rright,
AstMethods.IsTrue,
out tmp
);
return(Ast.Block(
new[] { temp, tmp },
res
));
}
internal static MSA.Expression /*!*/ TransformRead(AstGenerator /*!*/ gen, MSA.Expression /*!*/ left, MSA.Expression /*!*/ right)
{
MSA.ParameterExpression temp;
MSA.Expression result = AstUtils.CoalesceTrue(
AstFactory.Box(left),
AstFactory.Box(right),
Methods.IsTrue,
out temp
);
gen.CurrentScope.AddHidden(temp);
return(result);
}