Implemented closure and therefore recursion

Interpreter.cs

@@ -6,6 +6,7 @@ using System.Collections.Immutable;
 using AST = Finn.AST;
 using System.Runtime.CompilerServices;
 using System.Net;
+using Finn.AST;
 
 namespace Finn;
 
@@ -80,14 +81,6 @@ public record NativeFunction(Func<object[], object> Function) : Callable
 	public override string ToString() => "<native func>";
 }
 
-public class UserFunction : Callable
-{
-	public object Call(Interpreter interpreter, object[] arguments)
-	{
-		throw new NotImplementedException();
-	}
-}
-
 public class Interpreter : AST.IExprVisitor<Env, object>
 {
 	private class PatternMismatchException : Exception
@@ -299,11 +292,25 @@ public class Interpreter : AST.IExprVisitor<Env, object>
 		}
 	}
 
-	private readonly Env globals = new Env();
+	public record FinnFunction(FuncBinding binding, Env closure) : Callable
+	{
+		public object Call(Interpreter interpreter, object[] arguments)
+		{
+			Env env = new Env(closure);
+			for (int i = 0; i < binding.Params.Length; i++)
+			{
+				binding.Params[i].accept((arguments[i], env), new PatternBinder());
+			}
+			return interpreter.evaluate(env, binding.Value);
+			// throw new NotImplementedException();
+		}
+	}
+
+	protected internal readonly Env Globals = new Env();
 
 	public Interpreter()
 	{
-		globals["clock"] = new NativeFunction((args) =>
+		Globals["clock"] = new NativeFunction((args) =>
 		{
 			return (double)DateTimeOffset.Now.ToUnixTimeSeconds();
 		});
@@ -313,7 +320,7 @@ public class Interpreter : AST.IExprVisitor<Env, object>
 	{
 		try
 		{
-			var value = evaluate(globals, expression);
+			var value = evaluate(Globals, expression);
 			Console.WriteLine(value);
 		}
 		catch (RuntimeError err)
@@ -475,14 +482,14 @@ public class Interpreter : AST.IExprVisitor<Env, object>
 		catch { return new Variant("nothing", null); }
 	}
 
-	public object visitLetExpr(Env env, AST.Let expr)
+	public object visitLetExpr(Env env, Let expr)
 	{
 		var newEnv = new Env(env);
 		foreach (var binding in expr.Bindings)
 		{
 			switch (binding)
 			{
-				case AST.VarBinding(var pattern, var valueExpr):
+				case VarBinding(var pattern, var valueExpr):
 					var value = evaluate(env, valueExpr);
 					try
 					{
@@ -496,8 +503,11 @@ public class Interpreter : AST.IExprVisitor<Env, object>
 						throw new RuntimeError(start, e.Message);
 					}
 					break;
+				case FuncBinding fb:
+					newEnv[(string)fb.Name.Literal!] = new FinnFunction(fb, newEnv);
+					break;
 				default:
-					throw new NotImplementedException("TODO function bindings");
+					throw new Exception("wtf there are no other binding types");
 			}
 		}
 		return evaluate(newEnv, expr.Body);

Parser.cs

@@ -237,8 +237,7 @@ class Parser
 		}
 		var letToken = previous();
 
-		List<Binding> bindings = new List<Binding>();
+		List<Binding> bindings = new List<Binding> { parseBinding() };
-		bindings.Add(parseBinding());
 		while (match(TokenType.And))
 		{
 			bindings.Add(parseBinding());
@@ -252,7 +251,7 @@ class Parser
 			Pattern p = pattern();
 			switch (p)
 			{
-				case (SimplePattern(var funcName)) when funcName != null && match(TokenType.LParen):
+				case SimplePattern(var funcName) when funcName != null && match(TokenType.LParen):
 					List<Pattern> funcParams = new List<Pattern>();
 					while (!check(TokenType.RParen))
 					{

TODO.txt

@@ -1,4 +1,4 @@
-Implement Finn functions
+Allow variable defs to reference earlier ones in same binding list
 Figure out multiple-binding let-expr semantics
 Inject error handling into parser and scanner
 Think about a way to hide record fields