Evaluate all non-binding expressions

Interpreter.cs

@@ -1,4 +1,5 @@
 using System;
+using System.Collections.Generic;
 using System.Collections.Immutable;
 
 using AST = Finn.AST;
@@ -27,13 +28,47 @@ public class Interpreter : AST.IExprVisitor<object>
 		}
 	}
 
+	private class List
+	{
+		public required ImmutableList<object> Items { get; init; }
+
+		public static List Empty = new List { Items = ImmutableList<object>.Empty };
+
+		public object this[double i]
+		{
+			get { return Items[(int)i]; }
+		}
+
+		public bool IsEmpty
+		{
+			get { return Items.IsEmpty; }
+		}
+
+		public List Add(object item)
+		{
+			return new List { Items = Items.Add(item) };
+		}
+
+		public override string ToString()
+		{
+			System.IO.StringWriter sw = new System.IO.StringWriter();
+			sw.Write("[");
+			foreach (var item in this.Items)
+			{
+				sw.Write($" {item},");
+			}
+			sw.Write(" ]");
+			return sw.ToString();
+		}
+	}
+
 	private class Record
 	{
 		public static Record Empty = new Record
 		{
-			Fields = ImmutableDictionary<string, ImmutableStack<object>>.Empty,
+			Fields = ImmutableSortedDictionary<string, ImmutableStack<object>>.Empty,
 		};
-		public required ImmutableDictionary<string, ImmutableStack<object>> Fields { get; init; }
+		public required ImmutableSortedDictionary<string, ImmutableStack<object>> Fields { get; init; }
 
 		public Record Update(string name, object value)
 		{
@@ -77,6 +112,21 @@ public class Interpreter : AST.IExprVisitor<object>
 			var values = Fields.GetValueOrDefault(name, ImmutableStack<object>.Empty);
 			return new Record { Fields = Fields.SetItem(name, values.Push(value)) };
 		}
+
+		public override string ToString()
+		{
+			System.IO.StringWriter sw = new System.IO.StringWriter();
+			sw.Write("{");
+			foreach ((var label, var values) in this.Fields)
+			{
+				foreach (var value in values)
+				{
+					sw.Write($" {label} = {value},");
+				}
+			}
+			sw.Write(" }");
+			return sw.ToString();
+		}
 	}
 
 	private record Variant(string Tag, object? Value)
@@ -120,9 +170,21 @@ public class Interpreter : AST.IExprVisitor<object>
 		return expr.accept(this);
 	}
 
-	private void checkNumberOperand(Token op, Object operand)
+	private List checkListOperand(Token op, Object operand)
 	{
-		if (operand is double) return;
+		if (operand is List l) return l;
+		throw new RuntimeError(op, "Operand must be a record.");
+	}
+
+	private Record checkRecordOperand(Token op, Object operand)
+	{
+		if (operand is Record r) return r;
+		throw new RuntimeError(op, "Operand must be a record.");
+	}
+
+	private double checkNumberOperand(Token op, Object operand)
+	{
+		if (operand is double d) return d;
 		throw new RuntimeError(op, "Operand must be a number.");
 	}
 
@@ -138,6 +200,15 @@ public class Interpreter : AST.IExprVisitor<object>
 		throw new RuntimeError(op, "Operands must be strings.");
 	}
 
+	private Variant checkBoolOperand(Token op, object operand)
+	{
+		if (operand is Variant v)
+		{
+			if (v == Variant.True || v == Variant.False) return v;
+		}
+		throw new RuntimeError(op, "Operand must be <true,false>.");
+	}
+
 	public object visitBinaryExpr(AST.Binary expr)
 	{
 		var left = evaluate(expr.Left);
@@ -202,7 +273,6 @@ public class Interpreter : AST.IExprVisitor<object>
 	public object visitGroupingExpr(AST.Grouping expr)
 	{
 		return evaluate(expr.Expression);
-		throw new System.NotImplementedException();
 	}
 
 	public object visitIdentifierExpr(AST.Identifier expr)
@@ -212,12 +282,31 @@ public class Interpreter : AST.IExprVisitor<object>
 
 	public object visitIfExpr(AST.If expr)
 	{
-		throw new System.NotImplementedException();
+		var cond = evaluate(expr.Condition);
+		// TODO Maybe I should token info in the AST.
+		var vb = checkBoolOperand(new Token(TokenType.If, "if", null, 1), cond);
+		if (vb == Variant.True)
+		{
+			return evaluate(expr.Then);
+		}
+		else
+		{
+			return evaluate(expr.Else);
+		}
 	}
 
 	public object visitIndexerExpr(AST.Indexer expr)
 	{
-		throw new System.NotImplementedException();
+		// TODO use real token
+		var tok = new Token(TokenType.LBracket, "[", null, 1);
+		var left = checkListOperand(tok, evaluate(expr.Left));
+		var index = checkNumberOperand(tok, evaluate(expr.Index));
+		try
+		{
+			var item = left[index];
+			return new Variant("some", item);
+		}
+		catch { return new Variant("nothing", null); }
 	}
 
 	public object visitLetExpr(AST.Let expr)
@@ -227,7 +316,20 @@ public class Interpreter : AST.IExprVisitor<object>
 
 	public object visitListExpr(AST.List expr)
 	{
-		throw new System.NotImplementedException();
+		// TODO use real token
+		var tok = new Token(TokenType.LBracket, "[", null, 1);
+		List l = List.Empty;
+		foreach (var itemExpr in expr.Elements)
+		{
+			var item = evaluate(itemExpr);
+			if (!l.IsEmpty)
+			{
+				try { checkTypesEqual(l[0], item); }
+				catch { throw new RuntimeError(tok, "List items must all have same type."); }
+			}
+			l = l.Add(item);
+		}
+		return l;
 	}
 
 	public object visitLiteralExpr(AST.Literal expr)
@@ -237,17 +339,79 @@ public class Interpreter : AST.IExprVisitor<object>
 
 	public object visitRecordExpr(AST.Record expr)
 	{
-		throw new System.NotImplementedException();
+		// TODO use real token
+		Token tok = new Token(TokenType.LBrace, "{", null, 1);
+		Record rec = Record.Empty;
+		if (expr.Base != null)
+		{
+			var baseRecValue = evaluate(expr.Base.Value);
+			if (baseRecValue is not Record)
+			{
+				throw new RuntimeError(tok, "Base record must be a record.");
+			}
+			var baseRec = (Record)baseRecValue;
+
+			// Updates
+			HashSet<string> updateLabels = new HashSet<string>();
+			foreach (AST.Field update in expr.Base.Updates)
+			{
+				var label = update.Name.Value;
+				if (updateLabels.Contains(label))
+				{
+					throw new RuntimeError(tok, "Record updates must be to unique fields.");
+				}
+				updateLabels.Add(label);
+				if (update.Value == null) throw new NotImplementedException();
+				try
+				{
+					baseRec = baseRec.Update(label, evaluate(update.Value));
+				}
+				catch
+				{
+					throw new RuntimeError(tok, "Field update must have same type as previous value.");
+				}
+			}
+			rec = baseRec;
+		}
+
+		// Extensions
+		HashSet<string> extLabels = new HashSet<string>();
+		foreach (AST.Field extension in expr.Extensions)
+		{
+			var label = extension.Name.Value;
+			if (extLabels.Contains(label))
+			{
+				throw new RuntimeError(tok, "Record extensions must have unique field names.");
+
+			}
+			extLabels.Add(label);
+			if (extension.Value == null) throw new NotImplementedException();
+			rec = rec.Extend(label, evaluate(extension.Value));
+		}
+
+		return rec;
 	}
 
 	public object visitSelectorExpr(AST.Selector expr)
 	{
-		throw new System.NotImplementedException();
+		var left = evaluate(expr.Left);
+		// TODO Use real token.
+		var tok = new Token(TokenType.Period, ".", null, 1);
+		var r = checkRecordOperand(tok, left);
+		try
+		{
+			return r.Get(expr.FieldName.Value);
+		}
+		catch
+		{
+			throw new RuntimeError(tok, "Operand must have selected field.");
+		}
 	}
 
 	public object visitSequenceExpr(AST.Sequence expr)
 	{
-		throw new System.NotImplementedException();
+		evaluate(expr.Left);
+		return evaluate(expr.Right);
 	}
 
 	public object visitUnaryExpr(AST.Unary expr)
@@ -259,18 +423,14 @@ public class Interpreter : AST.IExprVisitor<object>
 				checkNumberOperand(expr.Op, right);
 				return -(double)right;
 			case TokenType.Bang:
-				if (right is Variant v)
+				if (checkBoolOperand(expr.Op, right) == Variant.True)
 				{
-					if (v == Variant.True)
+					return Variant.False;
-					{
+				}
-						return Variant.False;
+				else
-					}
+				{
-					else if (v == Variant.False)
+					return Variant.True;
-					{
-						return Variant.True;
-					}
 				}
-				throw new RuntimeError(expr.Op, "Boolean must be <true, false>");
 			default:
 				// Unreachable
 				throw new Exception($"bad unary op: {expr.Op}");
@@ -279,7 +439,7 @@ public class Interpreter : AST.IExprVisitor<object>
 
 	public object visitVariantExpr(AST.Variant expr)
 	{
-		throw new System.NotImplementedException();
+		return new Variant(expr.Tag.Value, expr.Argument);
 	}
 
 	public object visitWhenExpr(AST.When expr)