Return a dictionary of resolutions from Resolver

AST.cs

@@ -2,7 +2,7 @@ using System.Collections.Generic;
 
 namespace Finn.AST;
 
-public record Field(Token Name, Expr? Value);
+public record Field(Token Name, Expr Value);
 
 public record BaseRecord(Expr Value, Field[] Updates);
 

Parser.cs

@@ -491,7 +491,8 @@ class Parser
 			while (!check(endAt))
 			{
 				var fieldName = consume("Expect identifier as field name.", TokenType.Identifier, TokenType.QuotedIdentifier);
-				var value = match(TokenType.Equal) ? expression() : null;
+				// Desugar punned field.
+				var value = match(TokenType.Equal) ? expression() : new Variable(fieldName);
 				fields.Add(new(fieldName, value));
 				if (!match(TokenType.Comma))
 				{

Resolver.cs

@@ -1,11 +1,14 @@
 using System;
 using System.Collections.Immutable;
+using System.Linq;
 using Finn;
 using Finn.AST;
 
+using ScopeStack = System.Collections.Immutable.ImmutableStack<System.Collections.Immutable.ImmutableHashSet<string>>;
+using Resolutions = System.Collections.Immutable.ImmutableDictionary<Finn.AST.Expr, int>;
+using System.Collections.Generic;
 
-
+class Resolver : IExprVisitor<ScopeStack, Resolutions>
-class Resolver : IExprVisitor<ImmutableStack<ImmutableHashSet<string>>, ValueTuple>
 {
 	private class NameCollection
 	{
@@ -71,66 +74,59 @@ class Resolver : IExprVisitor<ImmutableStack<ImmutableHashSet<string>>, ValueTup
 		}
 	}
 
-	private static readonly ValueTuple Void = ValueTuple.Create();
+	private static readonly Resolutions EmptyResolutions = Resolutions.Empty.WithComparers(ReferenceEqualityComparer.Instance);
-	private readonly Interpreter Interpreter;
+	public static readonly Resolver Instance = new Resolver();
 
-	Resolver(Interpreter interpreter)
+	private Resolver() { }
+
+	private static Resolutions AddRange(Resolutions r1, Resolutions r2) => r1.AddRange(r2);
+
+	private Resolutions Resolve(ScopeStack scopes, Expr expr)
 	{
-		Interpreter = interpreter;
+		return expr.accept(scopes, this);
 	}
 
-	private void Resolve(ImmutableStack<ImmutableHashSet<string>> scopes, Expr expr)
+	private Resolutions Resolve(ScopeStack scopes, ImmutableHashSet<string> newScope, Expr value)
 	{
-		expr.accept(scopes, this);
+		return Resolve(scopes.Push(newScope), value);
 	}
 
-	private void Resolve(ImmutableStack<ImmutableHashSet<string>> scopes, ImmutableHashSet<string> newScope, Expr value)
+	public Resolutions visitBinaryExpr(ScopeStack scopes, Binary expr)
 	{
-		Resolve(scopes.Push(newScope), value);
+		var left = Resolve(scopes, expr.Left);
+		var right = Resolve(scopes, expr.Right);
+		return left.AddRange(right);
 	}
 
-	public ValueTuple visitBinaryExpr(ImmutableStack<ImmutableHashSet<string>> scopes, Binary expr)
+	public Resolutions visitCallExpr(ScopeStack scopes, Call expr)
 	{
-		Resolve(scopes, expr.Left);
+		return (from arg in expr.Arguments
-		Resolve(scopes, expr.Right);
+				where arg is not null
-		return Void;
+				select Resolve(scopes, arg))
+		.Aggregate(Resolve(scopes, expr.Left), AddRange);
 	}
 
-	public ValueTuple visitCallExpr(ImmutableStack<ImmutableHashSet<string>> scopes, Call expr)
+	public Resolutions visitGroupingExpr(ScopeStack scopes, Grouping expr)
 	{
-		Resolve(scopes, expr.Left);
+		return Resolve(scopes, expr.Expression);
-		foreach (var arg in expr.Arguments)
-		{
-			if (arg is not null)
-			{
-				Resolve(scopes, arg);
-			}
-		}
-		return Void;
 	}
 
-	public ValueTuple visitGroupingExpr(ImmutableStack<ImmutableHashSet<string>> scopes, Grouping expr)
+	public Resolutions visitIfExpr(ScopeStack scopes, If expr)
 	{
-		Resolve(scopes, expr.Expression);
+		var condition = Resolve(scopes, expr.Condition);
-		return Void;
+		var _then = Resolve(scopes, expr.Then);
+		var _else = Resolve(scopes, expr.Else);
+		return condition.AddRange(_then).AddRange(_else);
 	}
 
-	public ValueTuple visitIfExpr(ImmutableStack<ImmutableHashSet<string>> scopes, If expr)
+	public Resolutions visitIndexerExpr(ScopeStack scopes, Indexer expr)
 	{
-		Resolve(scopes, expr.Condition);
+		var left = Resolve(scopes, expr.Left);
-		Resolve(scopes, expr.Then);
+		var index = Resolve(scopes, expr.Index);
-		Resolve(scopes, expr.Else);
+		return left.AddRange(index);
-		return Void;
 	}
 
-	public ValueTuple visitIndexerExpr(ImmutableStack<ImmutableHashSet<string>> scopes, Indexer expr)
+	public Resolutions visitLetExpr(ScopeStack scopes, Let expr)
-	{
-		Resolve(scopes, expr.Left);
-		Resolve(scopes, expr.Index);
-		return Void;
-	}
-
-	public ValueTuple visitLetExpr(ImmutableStack<ImmutableHashSet<string>> scopes, Let expr)
 	{
 		var names = new NameCollection();
 		foreach (var binding in expr.Bindings)
@@ -154,140 +150,108 @@ class Resolver : IExprVisitor<ImmutableStack<ImmutableHashSet<string>>, ValueTup
 		//     For now, just check that a definition only uses names that come before it.
 		//     Note that this will preclude using shadowed variables in definitions.
 
-		foreach (var binding in expr.Bindings)
+		return (from binding in expr.Bindings
+				select (binding switch
 				{
-			switch (binding)
+					FuncBinding fb => ResolveFunction(newScopes, fb),
-			{
+					VarBinding vb => Resolve(newScopes, vb.Value),
-				case FuncBinding fb:
+					_ => throw new Exception("wtf there are no other binding types"),
-					ResolveFunction(newScopes, fb);
+				}))
-					break;
+				.Aggregate(Resolve(newScopes, expr.Body), AddRange);
-				case VarBinding vb:
-					Resolve(newScopes, vb.Value);
-					break;
-				default:
-					throw new Exception("wtf there are no other binding types");
-			}
-		}
-		Resolve(newScopes, expr.Body);
 
-		return Void;
 	}
 
-	private void ResolveFunction(ImmutableStack<ImmutableHashSet<string>> scopes, FuncBinding fb)
+	private Resolutions ResolveFunction(ScopeStack scopes, FuncBinding fb)
 	{
 		NameCollection names = new();
 		foreach (var param in fb.Params)
 		{
 			param.accept(names, PatternNameCollector.Instance);
 		}
-		Resolve(scopes, names.Names, fb.Value);
+		return Resolve(scopes, names.Names, fb.Value);
 	}
 
-	public ValueTuple visitListExpr(ImmutableStack<ImmutableHashSet<string>> scopes, List expr)
+	public Resolutions visitListExpr(ScopeStack scopes, List expr)
 	{
-		foreach (var element in expr.Elements)
+		return (from element in expr.Elements
-		{
+				select Resolve(scopes, element))
-			Resolve(scopes, element);
+				.Aggregate(EmptyResolutions, AddRange);
-		}
-		return Void;
 	}
 
-	public ValueTuple visitLiteralExpr(ImmutableStack<ImmutableHashSet<string>> scopes, Literal expr)
+	public Resolutions visitLiteralExpr(ScopeStack scopes, Literal expr)
 	{
-		return Void;
+		return EmptyResolutions;
 	}
 
-	public ValueTuple visitRecordExpr(ImmutableStack<ImmutableHashSet<string>> scopes, Record expr)
+	public Resolutions visitRecordExpr(ScopeStack scopes, Record expr)
 	{
+		var resolutions = (from extension in expr.Extensions
+						   select Resolve(scopes, extension.Value))
+						   .Aggregate(EmptyResolutions, AddRange);
 		if (expr.Base is not null)
 		{
-			Resolve(scopes, expr.Base.Value);
+			resolutions = resolutions.AddRange(Resolve(scopes, expr.Base.Value));
-			foreach (var update in expr.Base.Updates)
+			resolutions = (from update in expr.Base.Updates
-			{
+						   select Resolve(scopes, update.Value))
-				if (update.Value is not null)
+						  .Aggregate(resolutions, AddRange);
-				{
-					Resolve(scopes, update.Value);
-				}
-				else
-				{
-					// TODO Resolve update.Name like a var expression.
-				}
-			}
-		}
-		foreach (var extension in expr.Extensions)
-		{
-			if (extension.Value is not null)
-			{
-				Resolve(scopes, extension.Value);
-			}
-			else
-			{
-				// TODO Resolve extension.Name like a var expression.
-			}
-		}
-		return Void;
 		}
 
-	public ValueTuple visitSelectorExpr(ImmutableStack<ImmutableHashSet<string>> scopes, Selector expr)
+		return resolutions;
-	{
-		Resolve(scopes, expr.Left);
-		return Void;
 	}
 
-	public ValueTuple visitSequenceExpr(ImmutableStack<ImmutableHashSet<string>> scopes, Sequence expr)
+	public Resolutions visitSelectorExpr(ScopeStack scopes, Selector expr)
 	{
-		Resolve(scopes, expr.Left);
+		return Resolve(scopes, expr.Left);
-		Resolve(scopes, expr.Right);
-		return Void;
 	}
 
-	public ValueTuple visitUnaryExpr(ImmutableStack<ImmutableHashSet<string>> scopes, Unary expr)
+	public Resolutions visitSequenceExpr(ScopeStack scopes, Sequence expr)
 	{
-		Resolve(scopes, expr.Right);
+		return AddRange(Resolve(scopes, expr.Left), Resolve(scopes, expr.Right));
-		return Void;
 	}
 
-	public ValueTuple visitVariableExpr(ImmutableStack<ImmutableHashSet<string>> scopes, Variable expr)
+	public Resolutions visitUnaryExpr(ScopeStack scopes, Unary expr)
 	{
-		ResolveLocal(scopes, expr, expr.Value);
+		return Resolve(scopes, expr.Right);
-		return Void;
 	}
 
-	private void ResolveLocal(ImmutableStack<ImmutableHashSet<string>> scopes, Expr expr, Token name)
+	public Resolutions visitVariableExpr(ScopeStack scopes, Variable expr)
 	{
 		int depth = 0;
 		while (!scopes.IsEmpty)
 		{
 			scopes = scopes.Pop(out var scope);
-			if (scope.Contains((string)name.Literal!))
+			if (scope.Contains((string)expr.Value.Literal!))
 			{
-				Interpreter.Resolve(expr, depth);
+				return EmptyResolutions.Add(expr, depth);
-				return;
 			}
 			depth++;
 		}
 		// At this point, it must be a global. I don't like that we leave that resolution for runtime.
 		// TODO Don't leave that resolution for runtime.
+		// But I think that can wait until I make the resolver nameless.
+		return EmptyResolutions.Add(expr, depth);
 	}
 
-	public ValueTuple visitVariantExpr(ImmutableStack<ImmutableHashSet<string>> scopes, Variant expr)
+	public Resolutions visitVariantExpr(ScopeStack scopes, Variant expr)
 	{
 		if (expr.Argument is not null)
 		{
-			Resolve(scopes, expr.Argument);
+			return Resolve(scopes, expr.Argument);
 		}
-		return Void;
+		return EmptyResolutions;
 	}
 
-	public ValueTuple visitWhenExpr(ImmutableStack<ImmutableHashSet<string>> scopes, When expr)
+	public Resolutions visitWhenExpr(ScopeStack scopes, When expr)
 	{
-		Resolve(scopes, expr.Head);
+		return (from _case in expr.Cases
-		foreach (var _case in expr.Cases)
+				select ResolveCase(_case))
+		.Aggregate(Resolve(scopes, expr.Head), AddRange);
+
+		Resolutions ResolveCase(VarBinding _case)
 		{
 			var names = new NameCollection();
 			_case.Pattern.accept(names, PatternNameCollector.Instance);
-			Resolve(scopes, names.Names, _case.Value);
+			return Resolve(scopes, names.Names, _case.Value);
-		}
+		}
-		return Void;
 	}
 }

TODO.txt

@@ -1,3 +1,8 @@
+Wire up resolver to interpreter
+Move let-expr resolvability check to Resolver
+Remove dynamic type checks (checkXXX methods) from interpreter
+Use numerical indices in resolutions
+Statically resolve global references
 Capitalize stuff to match common C# style
 Replace `with` keyword with `but`
 Figure out multiple-binding let-expr semantics