public override IUnboundExpr Transform(LetExpr expr)
{
// a let expression desugars like this:
//
// let a b <- Foo then Bar else Bang
//
// becomes...
//
// def let__ <- Foo
// if Some? let__ then
// def a b <- 0 SomeValue let__
// Bar
// else Bang
var c = new CodeBuilder(mNameGenerator, expr.Position);
var option = c.TempName();
return c.Block(
c.Def(option, expr.Condition),
c.If(c.Call("Some?", option),
c.Block(
c.Def(expr.Names, c.Call("SomeValue", option)),
expr.ThenBody),
expr.ElseBody));
}
public override IUnboundExpr Transform(LoopExpr expr)
{
// a for expression is basically syntactic sugar for a while expression
// and one or more iterators. for example, the following:
//
// for foo <- bar do
// Print foo
// end
//
// is equivalent to:
//
// def _fooIter <- Iterate bar
// while MoveNext _fooIter do
// def foo <- Current _fooIter
// Print foo
// end
//
// so, to bind a for expression, we just desugar it, then bind that.
var c = new CodeBuilder(mNameGenerator, expr.Position);
var topExprs = new List<IUnboundExpr>();
var conditionExpr = (IUnboundExpr)null;
var whileExprs = new List<IUnboundExpr>();
// instantiate each clause
foreach (var clause in expr.Clauses)
{
c.SetPosition(clause.Position);
var condition = (IUnboundExpr)null;
if (clause.IsWhile)
{
condition = clause.Expression;
}
else
{
var iterName = mNameGenerator.Generate();
topExprs.Add(c.Def(iterName, c.Call("Iterate", clause.Expression)));
whileExprs.Add(c.Def(clause.Name, c.Call("Current", iterName)));
condition = c.Call("MoveNext", iterName);
}
if (conditionExpr == null)
{
conditionExpr = condition;
}
else
{
// combine with previous condition(s)
conditionExpr = c.Op(conditionExpr, "&", condition);
}
}
// create the while loop
c.SetPosition(expr.Position);
whileExprs.Add(expr.Body);
var whileExpr = c.While(
conditionExpr,
c.Block(whileExprs));
topExprs.Add(whileExpr);
// build the whole block
return c.Block(topExprs);
}
private MagpieParser(IEnumerable<Token> tokens)
: base(tokens)
{
mC = new CodeBuilder(null);
}
public override IUnboundExpr Transform(LoopExpr expr)
{
// a for expression is basically syntactic sugar for a while expression
// and one or more iterators. for example, the following:
//
// for foo <- bar do
// Print foo
// end
//
// is equivalent to:
//
// def _fooIter <- Iterate bar
// while MoveNext _fooIter do
// def foo <- Current _fooIter
// Print foo
// end
//
// so, to bind a for expression, we just desugar it, then bind that.
var c = new CodeBuilder(mNameGenerator, expr.Position);
var topExprs = new List<IUnboundExpr>();
var conditionExpr = (IUnboundExpr)null;
var whileExprs = new List<IUnboundExpr>();
// instantiate each clause
foreach (var clause in expr.Clauses)
{
c.SetPosition(clause.Position);
var condition = (IUnboundExpr)null;
if (clause.IsWhile)
{
condition = clause.Expression;
}
else
{
var iterName = mNameGenerator.Generate();
topExprs.Add(c.Def(iterName, c.Call("Iterate", clause.Expression)));
whileExprs.Add(c.Def(clause.Name, c.Call("Current", iterName)));
condition = c.Call("MoveNext", iterName);
}
if (conditionExpr == null)
{
conditionExpr = condition;
}
else
{
// combine with previous condition(s)
conditionExpr = c.Op(conditionExpr, "&", condition);
}
}
// create the while loop
c.SetPosition(expr.Position);
whileExprs.Add(expr.Body);
var whileExpr = c.While(
conditionExpr,
c.Block(whileExprs));
topExprs.Add(whileExpr);
// build the whole block
return c.Block(topExprs);
}
