public void DoEmitPartialApplicationCode(CompilerTarget target)
{
AstPlaceholder.DeterminePlaceholderIndices(Expressions.OfType<AstPlaceholder>());
var count = Expressions.Count;
if (count == 0)
{
this.ConstFunc(null).EmitValueCode(target);
return;
}
//only the very last condition may be a placeholder
for (var i = 0; i < count; i++)
{
var value = Expressions[i];
var isPlaceholder = value.IsPlaceholder();
if (i == count - 1)
{
if (!isPlaceholder)
{
//there is no placeholder at all, wrap expression in const
Debug.Assert(Expressions.All(e => !e.IsPlaceholder()));
DoEmitCode(target,StackSemantics.Value);
target.EmitCommandCall(Position, 1, Const.Alias);
return;
}
}
else
{
if (isPlaceholder)
{
_reportInvalidPlaceholders(target);
return;
}
}
}
if (count == 0)
{
this.ConstFunc().EmitValueCode(target);
}
else if (count == 1)
{
Debug.Assert(Expressions[0].IsPlaceholder(),
"Singleton ??-chain expected to consist of placeholder.");
var placeholder = (AstPlaceholder) Expressions[0];
placeholder.IdFunc().EmitValueCode(target);
}
else
{
Debug.Assert(Expressions[count - 1].IsPlaceholder(),
"Last expression in ??-chain expected to be placeholder.");
var placeholder = (AstPlaceholder) Expressions[count - 1];
var prefix = new AstCoalescence(File, Line, Column);
prefix.Expressions.AddRange(Expressions.Take(count - 1));
//check for null (keep a copy of prefix on stack)
var constLabel = _generateEndLabel();
var endLabel = _generateEndLabel();
prefix._emitCode(target, constLabel, StackSemantics.Value);
target.EmitDuplicate(Position);
target.Emit(Position,OpCode.check_null);
target.EmitJumpIfFalse(Position, constLabel);
//prefix is null, identity function
target.EmitPop(Position);
placeholder.IdFunc().EmitValueCode(target);
target.EmitJump(Position, endLabel);
//prefix is not null, const function
target.EmitLabel(Position, constLabel);
target.EmitCommandCall(Position, 1, Const.Alias);
target.EmitLabel(Position, endLabel);
}
}
private void _emitCode(CompilerTarget target, string endLabel, StackSemantics stackSemantics)
{
for (var i = 0; i < _expressions.Count; i++)
{
var expr = _expressions[i];
// Value semantics: duplicate of previous, rejected value needs to be popped
// Effect semantics: no duplicates were created in the first place
if (i > 0 && stackSemantics == StackSemantics.Value)
target.EmitPop(Position);
//For value semantics, we always generate a value
//For effect semantics, we only need the intermediate expressions to create a value
StackSemantics needValue;
if (stackSemantics == StackSemantics.Value || i < _expressions.Count - 1)
needValue = StackSemantics.Value;
else
needValue = StackSemantics.Effect;
expr.EmitCode(target, needValue);
//The last element doesn't need special handling, control just
// falls into the surrounding code with the correct value on top of the stack
if (i + 1 >= _expressions.Count)
continue;
if(stackSemantics == StackSemantics.Value)
target.EmitDuplicate(Position);
target.Emit(Position,OpCode.check_null);
target.EmitJumpIfFalse(Position, endLabel);
}
}
