public static DotFunc Equals()
{
return(DotFunc.From(
args =>
{
switch (args)
{
case DotSymbol _:
return DotBool.True();
case DotList l:
{
// TODO: extend equality to objects!
var numbers = l.Expressions.Cast <DotNumber>().ToList();
if (numbers.Count == 0)
{
throw new EvaluatorException("Nothing to compare.");
}
var first = numbers[0];
var(_, result) = numbers.Skip(1).Aggregate(
seed: (first, true), func: (tuple, b) =>
{
var(a, resultSoFar) = tuple;
if (!resultSoFar)
{
return (b, false);
}
var predicateStillTrue =
a.GetValue() == b.GetValue();
return (b, predicateStillTrue);
});
return new DotBool(result);
}
}
return DotBool.False();
}));
}
public static DotExpression Expand(DotExpression expression,
bool topLevel = false)
{
if (!(expression is DotList l))
{
// constants can't be expanded
return(expression);
}
if (l.Expressions.Count == 0)
{
throw new ParserException(
"An empty list needs to be quoted!", l.Line, l.Column);
}
var args = l.Expressions.Skip(1).ToList();
// if (!(l.Expressions.First() is DotSymbol op))
// {
// throw new EvaluatorException(
// "Function or special form expected!");
// }
if (l.Expressions.First() is DotSymbol op)
{
if (op.Name == "quote")
{
return(expression);
}
// TODO Find a generic way to check function and procedure argument length and type
if (op.Name == "def" || op.Name == "defmacro")
{
if (args.Count != 2)
{
throw new ParserException("name and body expected!", op.Line,
op.Column);
}
var defBody = Expand(args.ElementAt(1));
if (op.Name == "defmacro")
{
if (!topLevel)
{
throw new ParserException(
"'defmacro' only allowed at top level!", op.Line,
op.Column);
}
var procedure = Evaluator.Eval(defBody);
if (!(procedure is DotProcedure dp))
{
throw new ParserException(
"A macro must be a procedure", op.Line, op.Column);
}
// Add macro
GlobalEnvironment.MacroTable.Add(
(args.ElementAt(0) as DotSymbol).Name,
dp
);
return(DotBool.True());
}
var expandedDefinition = new LinkedList <DotExpression>();
expandedDefinition.AddLast(op);
expandedDefinition.AddLast(args.First());
expandedDefinition.AddLast(defBody);
return(new DotList()
{
Expressions = expandedDefinition
});
}
if (op.Name == "quasiquote")
{
return(ExpandQuasiquote(args.First()));
}
if (GlobalEnvironment.MacroTable.ContainsKey(op.Name))
{
// call macro
var macro = GlobalEnvironment.MacroTable[op.Name];
var macroArgs = new DotList()
{
Expressions = args.ToLinkedList()
};
return(Expand(macro.Call(macroArgs), topLevel));
}
}
l.Expressions = l.Expressions
.Select(exp => Expand(exp, false))
.ToLinkedList();
return(l);
}
public static DotBool ToDotBool(this bool val)
{
return(val ? DotBool.True() : DotBool.False());
}