Evaluate let-exprs with simple bindings

Expr.g.cs

@@ -8,127 +8,127 @@
 namespace Finn.AST;
 
 public abstract record Expr() {
-	public abstract T accept<T>(IExprVisitor<T> visitor);
+	public abstract TResult accept<TContext, TResult>(TContext context, IExprVisitor<TContext, TResult> visitor);
 }
-public interface IExprVisitor<T> {
+public interface IExprVisitor<TContext, TResult> {
-	T visitSequenceExpr(Sequence expr);
+	TResult visitSequenceExpr(TContext context, Sequence expr);
-	T visitBinaryExpr(Binary expr);
+	TResult visitBinaryExpr(TContext context, Binary expr);
-	T visitGroupingExpr(Grouping expr);
+	TResult visitGroupingExpr(TContext context, Grouping expr);
-	T visitLiteralExpr(Literal expr);
+	TResult visitLiteralExpr(TContext context, Literal expr);
-	T visitUnaryExpr(Unary expr);
+	TResult visitUnaryExpr(TContext context, Unary expr);
-	T visitIfExpr(If expr);
+	TResult visitIfExpr(TContext context, If expr);
-	T visitVariableExpr(Variable expr);
+	TResult visitVariableExpr(TContext context, Variable expr);
-	T visitListExpr(List expr);
+	TResult visitListExpr(TContext context, List expr);
-	T visitVariantExpr(Variant expr);
+	TResult visitVariantExpr(TContext context, Variant expr);
-	T visitRecordExpr(Record expr);
+	TResult visitRecordExpr(TContext context, Record expr);
-	T visitSelectorExpr(Selector expr);
+	TResult visitSelectorExpr(TContext context, Selector expr);
-	T visitIndexerExpr(Indexer expr);
+	TResult visitIndexerExpr(TContext context, Indexer expr);
-	T visitCallExpr(Call expr);
+	TResult visitCallExpr(TContext context, Call expr);
-	T visitLetExpr(Let expr);
+	TResult visitLetExpr(TContext context, Let expr);
-	T visitWhenExpr(When expr);
+	TResult visitWhenExpr(TContext context, When expr);
 }
 public partial record Sequence(Expr Left, Expr Right) : Expr()
 {
-	public override T accept<T>(IExprVisitor<T> visitor)
+	public override TResult accept<TContext, TResult>(TContext context, IExprVisitor<TContext, TResult> visitor)
 	{
-		return visitor.visitSequenceExpr(this);
+		return visitor.visitSequenceExpr(context, this);
 	}
 }
 public partial record Binary(Expr Left, Token Op, Expr Right) : Expr()
 {
-	public override T accept<T>(IExprVisitor<T> visitor)
+	public override TResult accept<TContext, TResult>(TContext context, IExprVisitor<TContext, TResult> visitor)
 	{
-		return visitor.visitBinaryExpr(this);
+		return visitor.visitBinaryExpr(context, this);
 	}
 }
 public partial record Grouping(Expr Expression) : Expr()
 {
-	public override T accept<T>(IExprVisitor<T> visitor)
+	public override TResult accept<TContext, TResult>(TContext context, IExprVisitor<TContext, TResult> visitor)
 	{
-		return visitor.visitGroupingExpr(this);
+		return visitor.visitGroupingExpr(context, this);
 	}
 }
 public partial record Literal(System.Object Value) : Expr()
 {
-	public override T accept<T>(IExprVisitor<T> visitor)
+	public override TResult accept<TContext, TResult>(TContext context, IExprVisitor<TContext, TResult> visitor)
 	{
-		return visitor.visitLiteralExpr(this);
+		return visitor.visitLiteralExpr(context, this);
 	}
 }
 public partial record Unary(Token Op, Expr Right) : Expr()
 {
-	public override T accept<T>(IExprVisitor<T> visitor)
+	public override TResult accept<TContext, TResult>(TContext context, IExprVisitor<TContext, TResult> visitor)
 	{
-		return visitor.visitUnaryExpr(this);
+		return visitor.visitUnaryExpr(context, this);
 	}
 }
 public partial record If(Expr Condition, Expr Then, Expr Else) : Expr()
 {
-	public override T accept<T>(IExprVisitor<T> visitor)
+	public override TResult accept<TContext, TResult>(TContext context, IExprVisitor<TContext, TResult> visitor)
 	{
-		return visitor.visitIfExpr(this);
+		return visitor.visitIfExpr(context, this);
 	}
 }
 public partial record Variable(Name Value) : Expr()
 {
-	public override T accept<T>(IExprVisitor<T> visitor)
+	public override TResult accept<TContext, TResult>(TContext context, IExprVisitor<TContext, TResult> visitor)
 	{
-		return visitor.visitVariableExpr(this);
+		return visitor.visitVariableExpr(context, this);
 	}
 }
 public partial record List(Expr[] Elements) : Expr()
 {
-	public override T accept<T>(IExprVisitor<T> visitor)
+	public override TResult accept<TContext, TResult>(TContext context, IExprVisitor<TContext, TResult> visitor)
 	{
-		return visitor.visitListExpr(this);
+		return visitor.visitListExpr(context, this);
 	}
 }
 public partial record Variant(Name Tag, Expr? Argument) : Expr()
 {
-	public override T accept<T>(IExprVisitor<T> visitor)
+	public override TResult accept<TContext, TResult>(TContext context, IExprVisitor<TContext, TResult> visitor)
 	{
-		return visitor.visitVariantExpr(this);
+		return visitor.visitVariantExpr(context, this);
 	}
 }
 public partial record Record(Field[] Extensions, BaseRecord? Base) : Expr()
 {
-	public override T accept<T>(IExprVisitor<T> visitor)
+	public override TResult accept<TContext, TResult>(TContext context, IExprVisitor<TContext, TResult> visitor)
 	{
-		return visitor.visitRecordExpr(this);
+		return visitor.visitRecordExpr(context, this);
 	}
 }
 public partial record Selector(Expr Left, Name FieldName) : Expr()
 {
-	public override T accept<T>(IExprVisitor<T> visitor)
+	public override TResult accept<TContext, TResult>(TContext context, IExprVisitor<TContext, TResult> visitor)
 	{
-		return visitor.visitSelectorExpr(this);
+		return visitor.visitSelectorExpr(context, this);
 	}
 }
 public partial record Indexer(Expr Left, Expr Index) : Expr()
 {
-	public override T accept<T>(IExprVisitor<T> visitor)
+	public override TResult accept<TContext, TResult>(TContext context, IExprVisitor<TContext, TResult> visitor)
 	{
-		return visitor.visitIndexerExpr(this);
+		return visitor.visitIndexerExpr(context, this);
 	}
 }
 public partial record Call(Expr Left, Expr?[] Arguments) : Expr()
 {
-	public override T accept<T>(IExprVisitor<T> visitor)
+	public override TResult accept<TContext, TResult>(TContext context, IExprVisitor<TContext, TResult> visitor)
 	{
-		return visitor.visitCallExpr(this);
+		return visitor.visitCallExpr(context, this);
 	}
 }
 public partial record Let(Binding[] Bindings, Expr Body) : Expr()
 {
-	public override T accept<T>(IExprVisitor<T> visitor)
+	public override TResult accept<TContext, TResult>(TContext context, IExprVisitor<TContext, TResult> visitor)
 	{
-		return visitor.visitLetExpr(this);
+		return visitor.visitLetExpr(context, this);
 	}
 }
 public partial record When(Expr Head, Binding[] Cases) : Expr()
 {
-	public override T accept<T>(IExprVisitor<T> visitor)
+	public override TResult accept<TContext, TResult>(TContext context, IExprVisitor<TContext, TResult> visitor)
 	{
-		return visitor.visitWhenExpr(this);
+		return visitor.visitWhenExpr(context, this);
 	}
 }

Interpreter.cs

@@ -6,8 +6,6 @@ using AST = Finn.AST;
 
 namespace Finn;
 
-public class Interpreter : AST.IExprVisitor<object>
-{
 public class RuntimeError : Exception
 {
 	public readonly Token Token;
@@ -18,6 +16,55 @@ public class Interpreter : AST.IExprVisitor<object>
 	}
 }
 
+public class Env
+{
+	private readonly Env? enclosing;
+	private readonly Dictionary<string, object> values = new Dictionary<string, object>();
+
+	public Env()
+	{
+		this.enclosing = null;
+	}
+
+	public Env(Env enclosing)
+	{
+		this.enclosing = enclosing;
+	}
+
+	public object this[AST.Name name]
+	{
+		set
+		{
+			if (values.ContainsKey(name.Value))
+			{
+				// TODO use real location info
+				var tok = new Token(TokenType.Identifier, name.Value, null, 1);
+				throw new RuntimeError(tok, $"Cannot redefine variable {name} in same scope.");
+			}
+			values[name.Value] = value;
+		}
+		get
+		{
+			try
+			{
+				return values[name.Value];
+			}
+			catch
+			{
+				if (enclosing != null)
+				{
+					return enclosing[name];
+				}
+				// TODO use real location info
+				var tok = new Token(TokenType.Identifier, name.Value, null, 1);
+				throw new RuntimeError(tok, $"Undefined variable {name}.");
+			}
+		}
+	}
+}
+
+public class Interpreter : AST.IExprVisitor<Env, object>
+{
 	private static void checkTypesEqual(object a, object b)
 	{
 		var aType = a.GetType();
@@ -156,7 +203,7 @@ public class Interpreter : AST.IExprVisitor<object>
 	{
 		try
 		{
-			var value = evaluate(expression);
+			var value = evaluate(new Env(), expression);
 			Console.WriteLine(value);
 		}
 		catch (RuntimeError err)
@@ -165,9 +212,9 @@ public class Interpreter : AST.IExprVisitor<object>
 		}
 	}
 
-	private object evaluate(AST.Expr expr)
+	private object evaluate(Env env, AST.Expr expr)
 	{
-		return expr.accept(this);
+		return expr.accept(env, this);
 	}
 
 	private List checkListOperand(Token op, Object operand)
@@ -209,10 +256,10 @@ public class Interpreter : AST.IExprVisitor<object>
 		throw new RuntimeError(op, "Operand must be <true,false>.");
 	}
 
-	public object visitBinaryExpr(AST.Binary expr)
+	public object visitBinaryExpr(Env env, AST.Binary expr)
 	{
-		var left = evaluate(expr.Left);
+		var left = evaluate(env, expr.Left);
-		var right = evaluate(expr.Right);
+		var right = evaluate(env, expr.Right);
 
 		switch (expr.Op.type)
 		{
@@ -265,42 +312,42 @@ public class Interpreter : AST.IExprVisitor<object>
 		throw new ArgumentException($"bad binary op: {expr.Op}");
 	}
 
-	public object visitCallExpr(AST.Call expr)
+	public object visitCallExpr(Env env, AST.Call expr)
 	{
 		throw new System.NotImplementedException();
 	}
 
-	public object visitGroupingExpr(AST.Grouping expr)
+	public object visitGroupingExpr(Env env, AST.Grouping expr)
 	{
-		return evaluate(expr.Expression);
+		return evaluate(env, expr.Expression);
 	}
 
-	public object visitVariableExpr(AST.Variable expr)
+	public object visitVariableExpr(Env env, AST.Variable expr)
 	{
-		throw new System.NotImplementedException();
+		return env[expr.Value];
 	}
 
-	public object visitIfExpr(AST.If expr)
+	public object visitIfExpr(Env env, AST.If expr)
 	{
-		var cond = evaluate(expr.Condition);
+		var cond = evaluate(env, 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);
+			return evaluate(env, expr.Then);
 		}
 		else
 		{
-			return evaluate(expr.Else);
+			return evaluate(env, expr.Else);
 		}
 	}
 
-	public object visitIndexerExpr(AST.Indexer expr)
+	public object visitIndexerExpr(Env env, AST.Indexer expr)
 	{
 		// TODO use real token
 		var tok = new Token(TokenType.LBracket, "[", null, 1);
-		var left = checkListOperand(tok, evaluate(expr.Left));
+		var left = checkListOperand(tok, evaluate(env, expr.Left));
-		var index = checkNumberOperand(tok, evaluate(expr.Index));
+		var index = checkNumberOperand(tok, evaluate(env, expr.Index));
 		try
 		{
 			var item = left[index];
@@ -309,19 +356,42 @@ public class Interpreter : AST.IExprVisitor<object>
 		catch { return new Variant("nothing", null); }
 	}
 
-	public object visitLetExpr(AST.Let expr)
+	public object visitLetExpr(Env env, AST.Let expr)
 	{
-		throw new System.NotImplementedException();
+		var newEnv = new Env(env);
+		foreach (var binding in expr.Bindings)
+		{
+			switch (binding)
+			{
+				case AST.VarBinding(var pattern, var valueExpr):
+					switch (pattern)
+					{
+						case AST.SimplePattern(var identifier):
+							var value = evaluate(env, valueExpr);
+							if (identifier != null)
+							{
+								newEnv[identifier] = value;
+							}
+							break;
+						default:
+							throw new NotImplementedException("TODO moar patternz");
+					}
+					break;
+				default:
+					throw new NotImplementedException("TODO function bindings");
+			}
+		}
+		return evaluate(newEnv, expr.Body);
 	}
 
-	public object visitListExpr(AST.List expr)
+	public object visitListExpr(Env env, AST.List expr)
 	{
 		// 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);
+			var item = evaluate(env, itemExpr);
 			if (!l.IsEmpty)
 			{
 				try { checkTypesEqual(l[0], item); }
@@ -332,19 +402,19 @@ public class Interpreter : AST.IExprVisitor<object>
 		return l;
 	}
 
-	public object visitLiteralExpr(AST.Literal expr)
+	public object visitLiteralExpr(Env env, AST.Literal expr)
 	{
 		return expr.Value;
 	}
 
-	public object visitRecordExpr(AST.Record expr)
+	public object visitRecordExpr(Env env, AST.Record expr)
 	{
 		// 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);
+			var baseRecValue = evaluate(env, expr.Base.Value);
 			if (baseRecValue is not Record)
 			{
 				throw new RuntimeError(tok, "Base record must be a record.");
@@ -364,7 +434,7 @@ public class Interpreter : AST.IExprVisitor<object>
 				if (update.Value == null) throw new NotImplementedException();
 				try
 				{
-					baseRec = baseRec.Update(label, evaluate(update.Value));
+					baseRec = baseRec.Update(label, evaluate(env, update.Value));
 				}
 				catch
 				{
@@ -386,15 +456,15 @@ public class Interpreter : AST.IExprVisitor<object>
 			}
 			extLabels.Add(label);
 			if (extension.Value == null) throw new NotImplementedException();
-			rec = rec.Extend(label, evaluate(extension.Value));
+			rec = rec.Extend(label, evaluate(env, extension.Value));
 		}
 
 		return rec;
 	}
 
-	public object visitSelectorExpr(AST.Selector expr)
+	public object visitSelectorExpr(Env env, AST.Selector expr)
 	{
-		var left = evaluate(expr.Left);
+		var left = evaluate(env, expr.Left);
 		// TODO Use real token.
 		var tok = new Token(TokenType.Period, ".", null, 1);
 		var r = checkRecordOperand(tok, left);
@@ -408,15 +478,15 @@ public class Interpreter : AST.IExprVisitor<object>
 		}
 	}
 
-	public object visitSequenceExpr(AST.Sequence expr)
+	public object visitSequenceExpr(Env env, AST.Sequence expr)
 	{
-		evaluate(expr.Left);
+		evaluate(env, expr.Left);
-		return evaluate(expr.Right);
+		return evaluate(env, expr.Right);
 	}
 
-	public object visitUnaryExpr(AST.Unary expr)
+	public object visitUnaryExpr(Env env, AST.Unary expr)
 	{
-		object right = evaluate(expr.Right);
+		object right = evaluate(env, expr.Right);
 		switch (expr.Op.type)
 		{
 			case TokenType.Minus:
@@ -437,12 +507,12 @@ public class Interpreter : AST.IExprVisitor<object>
 		}
 	}
 
-	public object visitVariantExpr(AST.Variant expr)
+	public object visitVariantExpr(Env env, AST.Variant expr)
 	{
 		return new Variant(expr.Tag.Value, expr.Argument);
 	}
 
-	public object visitWhenExpr(AST.When expr)
+	public object visitWhenExpr(Env env, AST.When expr)
 	{
 		throw new System.NotImplementedException();
 	}

Pattern.g.cs

@@ -8,39 +8,39 @@
 namespace Finn.AST;
 
 public abstract record Pattern() {
-	public abstract T accept<T>(IPatternVisitor<T> visitor);
+	public abstract TResult accept<TContext, TResult>(TContext context, IPatternVisitor<TContext, TResult> visitor);
 }
-public interface IPatternVisitor<T> {
+public interface IPatternVisitor<TContext, TResult> {
-	T visitSimplePatternPattern(SimplePattern pattern);
+	TResult visitSimplePatternPattern(TContext context, SimplePattern pattern);
-	T visitVariantPatternPattern(VariantPattern pattern);
+	TResult visitVariantPatternPattern(TContext context, VariantPattern pattern);
-	T visitFieldPatternPattern(FieldPattern pattern);
+	TResult visitFieldPatternPattern(TContext context, FieldPattern pattern);
-	T visitRecordPatternPattern(RecordPattern pattern);
+	TResult visitRecordPatternPattern(TContext context, RecordPattern pattern);
 }
 public partial record SimplePattern(Name? Identifier) : Pattern()
 {
-	public override T accept<T>(IPatternVisitor<T> visitor)
+	public override TResult accept<TContext, TResult>(TContext context, IPatternVisitor<TContext, TResult> visitor)
 	{
-		return visitor.visitSimplePatternPattern(this);
+		return visitor.visitSimplePatternPattern(context, this);
 	}
 }
 public partial record VariantPattern(Name Tag, Pattern? Argument) : Pattern()
 {
-	public override T accept<T>(IPatternVisitor<T> visitor)
+	public override TResult accept<TContext, TResult>(TContext context, IPatternVisitor<TContext, TResult> visitor)
 	{
-		return visitor.visitVariantPatternPattern(this);
+		return visitor.visitVariantPatternPattern(context, this);
 	}
 }
 public partial record FieldPattern(Name Name, Pattern? Pattern) : Pattern()
 {
-	public override T accept<T>(IPatternVisitor<T> visitor)
+	public override TResult accept<TContext, TResult>(TContext context, IPatternVisitor<TContext, TResult> visitor)
 	{
-		return visitor.visitFieldPatternPattern(this);
+		return visitor.visitFieldPatternPattern(context, this);
 	}
 }
 public partial record RecordPattern(FieldPattern[] Fields, SimplePattern? Rest) : Pattern()
 {
-	public override T accept<T>(IPatternVisitor<T> visitor)
+	public override TResult accept<TContext, TResult>(TContext context, IPatternVisitor<TContext, TResult> visitor)
 	{
-		return visitor.visitRecordPatternPattern(this);
+		return visitor.visitRecordPatternPattern(context, this);
 	}
 }

Program.cs

@@ -84,7 +84,7 @@ class Program
 		}
 	}
 
-	public static void runtimeError(Interpreter.RuntimeError err)
+	public static void runtimeError(RuntimeError err)
 	{
 		Console.Error.WriteLine($"{err.Message}\n[line {err.Token.line}]");
 		hadRuntimeError = true;

ast_classes.fsx

@@ -64,10 +64,10 @@ let patternTypes =
 let visitorMethod baseName t = $"visit{t.Name}{baseName}"
 
 let renderIVisitor (sw: System.IO.StreamWriter) (baseName: string) types =
-    sw.Write($"public interface I{baseName}Visitor<T> {{\n")
+    sw.Write($"public interface I{baseName}Visitor<TContext, TResult> {{\n")
 
     for t in types do
-        sw.Write($"\tT {visitorMethod baseName t}({t.Name} {baseName.ToLower()});\n")
+        sw.Write($"\tTResult {visitorMethod baseName t}(TContext context, {t.Name} {baseName.ToLower()});\n")
 
     sw.Write("}\n")
 
@@ -86,9 +86,9 @@ let renderType (sw: System.IO.StreamWriter) baseName t =
 {{\n"
 
     sw.Write
-        $"\tpublic override T accept<T>(I{baseName}Visitor<T> visitor)
+        $"\tpublic override TResult accept<TContext, TResult>(TContext context, I{baseName}Visitor<TContext, TResult> visitor)
 \t{{
-\t\treturn visitor.{visitorMethod baseName t}(this);
+\t\treturn visitor.{visitorMethod baseName t}(context, this);
 \t}}\n"
 
     sw.Write("}\n")
@@ -108,7 +108,7 @@ let renderAST outputDir baseName types =
 namespace Finn.AST;
 
 public abstract record {baseName}() {{
-\tpublic abstract T accept<T>(I{baseName}Visitor<T> visitor);
+\tpublic abstract TResult accept<TContext, TResult>(TContext context, I{baseName}Visitor<TContext, TResult> visitor);
 }}\n"
 
     renderIVisitor sw baseName types