From 6f3c82cad1cc5ecf6b5b2818ed7a6395d0a726fa Mon Sep 17 00:00:00 2001
From: Brandon Dyck <brandon@dyck.us>
Date: Sat, 1 Jul 2023 00:12:02 -0600
Subject: [PATCH] Added identifiers and field selectors to grammar

---
 AST.cs          |  3 +++
 ASTPrinter.cs   | 16 +++++++++++++
 Expr.g.cs       | 19 ++++++++++++++++
 Parser.cs       | 60 +++++++++++++++++++++++++++++++++++++++----------
 ast_classes.fsx |  6 ++++-
 5 files changed, 91 insertions(+), 13 deletions(-)
 create mode 100644 AST.cs

diff --git a/AST.cs b/AST.cs
new file mode 100644
index 0000000..4cd1572
--- /dev/null
+++ b/AST.cs
@@ -0,0 +1,3 @@
+namespace Finn.AST;
+
+public record Name(string Value, bool Quoted);
diff --git a/ASTPrinter.cs b/ASTPrinter.cs
index 9017e36..fbcb93f 100644
--- a/ASTPrinter.cs
+++ b/ASTPrinter.cs
@@ -39,6 +39,17 @@ class ASTPrinter : IVisitor<string>
 		return expr.Value.ToString() ?? "";
 	}
 
+	private string formatName(Name name)
+	{
+		if (name.Quoted) return $"@\"{name.Value}\"";
+		return name.Value;
+	}
+
+	public string visitIdentifierExpr(Identifier expr)
+	{
+		return formatName(expr.Value);
+	}
+
 	public string visitUnaryExpr(Unary expr)
 	{
 		return parenthesize(expr.Op.lexeme, expr.Right);
@@ -53,4 +64,9 @@ class ASTPrinter : IVisitor<string>
 	{
 		return parenthesize("seq", expr.Left, expr.Right);
 	}
+
+	public string visitSelectorExpr(Selector expr)
+	{
+		return parenthesize(".", expr.Left, new Identifier { Value = expr.FieldName });
+	}
 }
diff --git a/Expr.g.cs b/Expr.g.cs
index d743ae9..5b7533f 100644
--- a/Expr.g.cs
+++ b/Expr.g.cs
@@ -16,6 +16,8 @@ public interface IVisitor<T> {
 	T visitLiteralExpr(Literal expr);
 	T visitUnaryExpr(Unary expr);
 	T visitIfExpr(If expr);
+	T visitIdentifierExpr(Identifier expr);
+	T visitSelectorExpr(Selector expr);
 }
 public class Sequence : Expr
 {
@@ -71,3 +73,20 @@ public class If : Expr
 		return visitor.visitIfExpr(this);
 	}
 }
+public class Identifier : Expr
+{
+	public required Name Value { get; init; }
+	public override T accept<T>(IVisitor<T> visitor)
+	{
+		return visitor.visitIdentifierExpr(this);
+	}
+}
+public class Selector : Expr
+{
+	public required Expr Left { get; init; }
+	public required Name FieldName { get; init; }
+	public override T accept<T>(IVisitor<T> visitor)
+	{
+		return visitor.visitSelectorExpr(this);
+	}
+}
diff --git a/Parser.cs b/Parser.cs
index d4e2022..480525b 100644
--- a/Parser.cs
+++ b/Parser.cs
@@ -73,7 +73,15 @@ class Parser
 
 	private Token consume(TokenType type, string message)
 	{
-		if (check(type)) return advance();
+		return consume(new TokenType[] { type }, message);
+	}
+
+	private Token consume(TokenType[] types, string message)
+	{
+		foreach (var type in types)
+		{
+			if (check(type)) return advance();
+		}
 
 		throw error(peek(), message);
 	}
@@ -160,7 +168,7 @@ class Parser
 			Expr right = unary();
 			return new Unary { Op = op, Right = right };
 		}
-		return ifExpr();
+		return control();
 	}
 
 	private Expr control()
@@ -182,28 +190,56 @@ class Parser
 		return primary();
 	}
 
-	private Expr ifExpr()
+	private Name? name()
 	{
-		if (match(TokenType.If))
+		if (match(TokenType.Identifier))
 		{
-			Expr condition = expression();
-			consume(TokenType.Then, "Expect 'then' after condition.");
-			Expr thenCase = expression();
-			consume(TokenType.Else, "Expect 'else' after 'then' case.");
-			Expr elseCase = expression();
-			return new If { Condition = condition, Then = thenCase, Else = elseCase };
+			return new(previous().lexeme, false);
 		}
-
-		return primary();
+		if (match(TokenType.At))
+		{
+			Token literal = consume(TokenType.String, "Expect string literal after '@'.");
+			return new((string)(literal.literal ?? ""), true);
+		}
+		return null;
 	}
 
 	private Expr primary()
+	{
+		Expr expr = operand();
+		if (match(TokenType.Period))
+		{
+			Name? ident = name();
+			if (ident == null)
+			{
+				throw error(advance(), "Expect identifier after dot.");
+			}
+			return new Selector { Left = expr, FieldName = ident };
+		}
+		if (match(TokenType.LBracket))
+		{
+			throw new NotImplementedException("TODO index");
+		}
+		if (match(TokenType.LParen))
+		{
+			throw new NotImplementedException("TODO apply");
+		}
+		return expr;
+	}
+
+	private Expr operand()
 	{
 		if (match(TokenType.Number, TokenType.String))
 		{
 			return new Literal { Value = previous().literal };
 		}
 
+		var ident = name();
+		if (ident != null)
+		{
+			return new Identifier { Value = ident };
+		}
+
 		if (match(TokenType.LParen))
 		{
 			Expr expr = expression();
diff --git a/ast_classes.fsx b/ast_classes.fsx
index 5ecb21a..6945bb1 100644
--- a/ast_classes.fsx
+++ b/ast_classes.fsx
@@ -21,7 +21,11 @@ let types =
         Fields =
           [ { Type = "Expr"; Name = "Condition" }
             { Type = "Expr"; Name = "Then" }
-            { Type = "Expr"; Name = "Else" } ] } ]
+            { Type = "Expr"; Name = "Else" } ] }
+      { Name = "Identifier"
+        Fields = [ { Type = "Name"; Name = "Value" } ] }
+      { Name = "Selector"
+        Fields = [ { Type = "Expr"; Name = "Left" }; { Type = "Name"; Name = "FieldName" } ] } ]
 
 let visitorMethod baseName t = $"visit{t.Name}{baseName}"