Evaluate arithmetic expressions
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6459e39260
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b1607eebc6
289
Interpreter.cs
Normal file
289
Interpreter.cs
Normal file
@ -0,0 +1,289 @@
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using System;
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using System.Collections.Immutable;
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using AST = Finn.AST;
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namespace Finn;
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public class Interpreter : AST.IExprVisitor<object>
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{
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public class RuntimeError : Exception
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{
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public readonly Token Token;
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internal RuntimeError(Token token, String message) : base(message)
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{
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Token = token;
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}
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}
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private static void checkTypesEqual(object a, object b)
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{
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var aType = a.GetType();
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var bType = b.GetType();
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if (aType != bType)
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{
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throw new Exception("Type mismatch: {aType} != {bType}.");
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}
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}
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private class Record
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{
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public static Record Empty = new Record
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{
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Fields = ImmutableDictionary<string, ImmutableStack<object>>.Empty,
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};
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public required ImmutableDictionary<string, ImmutableStack<object>> Fields { get; init; }
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public Record Update(string name, object value)
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{
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ImmutableStack<object>? values;
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if (!Fields.TryGetValue(name, out values))
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{
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throw new ArgumentException($"no such field: {name}");
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}
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checkTypesEqual(value, values.Peek());
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return new Record { Fields = Fields.SetItem(name, values!.Pop().Push(value)) };
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}
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public object Get(string name)
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{
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ImmutableStack<object>? values;
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if (!Fields.TryGetValue(name, out values))
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{
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throw new ArgumentException($"no such field: {name}");
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}
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return values.Peek();
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}
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public Record Remove(string name)
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{
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ImmutableStack<object>? values;
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if (!Fields.TryGetValue(name, out values))
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{
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throw new ArgumentException($"no such field: {name}");
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}
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var value = values.Peek();
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var popped = values.Pop();
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if (popped.IsEmpty)
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{
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return new Record { Fields = Fields.Remove(name) };
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}
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return new Record { Fields = Fields.SetItem(name, popped) };
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}
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public Record Extend(string name, object value)
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{
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var values = Fields.GetValueOrDefault(name, ImmutableStack<object>.Empty);
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return new Record { Fields = Fields.SetItem(name, values.Push(value)) };
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}
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}
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private record Variant(string Tag, object? Value)
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{
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public static readonly Variant True = new Variant("true", null);
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public static readonly Variant False = new Variant("false", null);
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public static Variant FromBool(bool b)
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{
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return b ? True : False;
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}
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public bool IsEmpty { get { return Value == null; } }
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public override string ToString()
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{
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if (Value == null)
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{
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return $"`{Tag}";
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}
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else
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{
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return $"`{Tag}({Value})";
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}
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}
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}
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public void Interpret(AST.Expr expression)
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{
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try
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{
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var value = evaluate(expression);
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Console.WriteLine(value);
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}
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catch (RuntimeError err)
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{
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Program.runtimeError(err);
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}
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}
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private object evaluate(AST.Expr expr)
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{
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return expr.accept(this);
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}
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private void checkNumberOperand(Token op, Object operand)
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{
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if (operand is double) return;
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throw new RuntimeError(op, "Operand must be a number.");
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}
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private void checkNumberOperands(Token op, object left, object right)
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{
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if (left is double && right is double) return;
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throw new RuntimeError(op, "Operands must be numbers.");
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}
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private void checkStringOperands(Token op, object left, object right)
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{
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if (left is string && right is string) return;
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throw new RuntimeError(op, "Operands must be strings.");
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}
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public object visitBinaryExpr(AST.Binary expr)
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{
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var left = evaluate(expr.Left);
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var right = evaluate(expr.Right);
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switch (expr.Op.type)
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{
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case TokenType.Minus:
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checkNumberOperands(expr.Op, left, right);
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return (double)left - (double)right;
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case TokenType.Plus:
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checkNumberOperands(expr.Op, left, right);
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return (double)left + (double)right;
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case TokenType.Slash:
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checkNumberOperands(expr.Op, left, right);
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return (double)left / (double)right;
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case TokenType.Asterisk:
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checkNumberOperands(expr.Op, left, right);
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return (double)left * (double)right;
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case TokenType.PlusPlus:
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checkStringOperands(expr.Op, left, right);
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return (string)left + (string)right;
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case TokenType.Greater:
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checkNumberOperands(expr.Op, left, right);
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return Variant.FromBool((double)left > (double)right);
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case TokenType.GreaterEqual:
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checkNumberOperands(expr.Op, left, right);
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return Variant.FromBool((double)left >= (double)right);
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case TokenType.Less:
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checkNumberOperands(expr.Op, left, right);
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return Variant.FromBool((double)left < (double)right);
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case TokenType.LessEqual:
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checkNumberOperands(expr.Op, left, right);
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return Variant.FromBool((double)left <= (double)right);
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case TokenType.BangEqual:
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return Variant.FromBool((left, right) switch
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{
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(String l, String r) => l != r,
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(double l, double r) => l != r,
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_ => throw new ArgumentException(),
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});
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case TokenType.DoubleEqual:
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return Variant.FromBool((left, right) switch
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{
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(String l, String r) => l == r,
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(double l, double r) => l == r,
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_ => throw new ArgumentException(),
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});
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}
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throw new ArgumentException($"bad binary op: {expr.Op}");
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}
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public object visitCallExpr(AST.Call expr)
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{
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throw new System.NotImplementedException();
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}
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public object visitGroupingExpr(AST.Grouping expr)
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{
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return evaluate(expr.Expression);
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throw new System.NotImplementedException();
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}
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public object visitIdentifierExpr(AST.Identifier expr)
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{
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throw new System.NotImplementedException();
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}
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public object visitIfExpr(AST.If expr)
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{
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throw new System.NotImplementedException();
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}
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public object visitIndexerExpr(AST.Indexer expr)
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{
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throw new System.NotImplementedException();
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}
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public object visitLetExpr(AST.Let expr)
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{
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throw new System.NotImplementedException();
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}
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public object visitListExpr(AST.List expr)
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{
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throw new System.NotImplementedException();
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}
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public object visitLiteralExpr(AST.Literal expr)
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{
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return expr.Value;
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}
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public object visitRecordExpr(AST.Record expr)
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{
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throw new System.NotImplementedException();
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}
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public object visitSelectorExpr(AST.Selector expr)
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{
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throw new System.NotImplementedException();
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}
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public object visitSequenceExpr(AST.Sequence expr)
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{
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throw new System.NotImplementedException();
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}
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public object visitUnaryExpr(AST.Unary expr)
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{
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object right = evaluate(expr.Right);
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switch (expr.Op.type)
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{
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case TokenType.Minus:
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checkNumberOperand(expr.Op, right);
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return -(double)right;
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case TokenType.Bang:
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if (right is Variant v)
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{
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if (v == Variant.True)
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{
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return Variant.False;
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}
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else if (v == Variant.False)
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{
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return Variant.True;
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}
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}
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throw new RuntimeError(expr.Op, "Boolean must be <true, false>");
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default:
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// Unreachable
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throw new Exception($"bad unary op: {expr.Op}");
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}
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}
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public object visitVariantExpr(AST.Variant expr)
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{
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throw new System.NotImplementedException();
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}
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public object visitWhenExpr(AST.When expr)
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{
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throw new System.NotImplementedException();
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}
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}
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15
Program.cs
15
Program.cs
@ -7,7 +7,9 @@ namespace Finn;
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class Program
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{
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private static readonly Interpreter interpreter = new Interpreter();
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static bool hadError = false;
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static bool hadRuntimeError = true;
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static void Main(string[] args)
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{
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@ -30,6 +32,9 @@ class Program
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{
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var src = File.ReadAllText(path);
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run(src);
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if (hadError) Environment.Exit(65);
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if (hadRuntimeError) Environment.Exit(70);
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}
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static void run(string src)
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@ -39,13 +44,13 @@ class Program
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Parser parser = new Parser(tokens);
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Expr? expression = parser.parse();
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if (hadError || expression == null)
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if (hadError)
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{
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hadError = false;
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return;
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}
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Console.WriteLine(expression);
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interpreter.Interpret(expression!);
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}
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static void runPrompt()
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@ -79,6 +84,12 @@ class Program
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}
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}
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public static void runtimeError(Interpreter.RuntimeError err)
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{
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Console.Error.WriteLine($"{err.Message}\n[line {err.Token.line}]");
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hadRuntimeError = true;
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}
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static void report(int line, String where, String message)
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{
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Console.WriteLine($"[line {line}] Error{where}: {message}");
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