Upsilon/Upsilon/Binder/BoundStatements/BoundYieldStatement.cs

using System;
using System.Collections;
using System.Collections.Generic;
using Upsilon.BaseTypes;
using Upsilon.BaseTypes.ScriptFunction;
using Upsilon.Evaluator;
using Upsilon.Exceptions;
using Upsilon.Text;
using Type = Upsilon.BaseTypes.Type;

namespace Upsilon.Binder
{
    public class BoundYieldStatement : BoundStatement
    {
        public BoundExpression Expression { get; }

        public BoundYieldStatement(BoundExpression expression, TextSpan span) : base(span)
        {
            Expression = expression;
        }

        public override BoundKind Kind => BoundKind.BoundYieldStatement;
        public override IEnumerable<BoundNode> GetChildren()
        {
            yield return Expression;
        }

        internal override void Evaluate(EvaluationScope scope, Diagnostics diagnostics, ref EvaluationState state)
        {
            throw new EvaluationException(state.Script.FileName,
                "Yielding in a function that's not executed as a coroutine is not possible.", Span);
        }

        internal override IEnumerator EvaluateCoroutine(EvaluationScope scope, Diagnostics diagnostics, EvaluationState state)
        {
            if (Expression.Kind == BoundKind.BoundFunctionCallExpression)
            {
                var functionCall = (BoundFunctionCallExpression) Expression;
                var variable = functionCall.Identifier.Evaluate(scope, diagnostics, ref state);
                if (!(variable is ScriptFunction function))
                {
                    throw new EvaluationException(state.Script.FileName, $"Variable is not a function.", functionCall.Identifier.Span);
                }

                if (function.IsCoroutine)
                {
                    var ls = new List<ScriptType>();
                    foreach (var t in functionCall.Parameters)
                    {
                        var evaluate = t.Evaluate(scope, diagnostics, ref state);
                        ls.Add(evaluate);
                    }
                    var coroutine = function.RunCoroutine(diagnostics, ls.ToArray(), scope, Span, state);
                    while (coroutine.MoveNext())
                    {
                        yield return coroutine.Current;
                    }
                    yield break;
                }
            }
            var value = Expression.Evaluate(scope, diagnostics, ref state);
            yield return value;
        }
    }
}