meowlang/typechecker/types/GenericTypeDescription.cs

namespace meowlang.typechecker;

public abstract record GenericTypeDescription : TypeDescription
{
    protected readonly List<string> GenericNames;

    public int Arity => GenericNames.Count;

    public GenericTypeDescription(List<string> genericNames)
    {
        GenericNames = genericNames;
    }

    protected void CheckGenericNames(List<GenericTypeId> genericTypes)
    {
        foreach (var typeId in genericTypes)
        {
            if (typeId.Key.IsGeneric)
            {
                if (GenericNames.IndexOf(typeId.Key.GenericParameterName!) < 0)
                {
                    throw new UndeclaredGenericParameterException(typeId.Key.GenericParameterName!);
                }
            }

            CheckGenericNames(typeId.GenericParams);
        }
    }
    public abstract TypeDescription Concretize(List<Guid> typeParams);
    
    

    protected TypeId ConcretizeGenericType(GenericTypeId genericType, List<Guid> concreteTypes)
    {
        return new TypeId(ConcretizeGenericTypeRef(genericType.Key, concreteTypes),
            genericType.GenericParams.Select(x => ConcretizeGenericType(x, concreteTypes)).ToList());
    }

    private Guid ConcretizeGenericTypeRef(PossiblyGenericTypeRef typeRef, List<Guid> concreteTypes)
    {
        if (!typeRef.IsGeneric) return typeRef.TypeKey!.Value;
        var typeIndex = GenericNames.IndexOf(typeRef.GenericParameterName!);
        return concreteTypes[typeIndex];
    }
}