IF statements

BasicNumber.cs

@@ -15,7 +15,7 @@ namespace SuperBASIC
 	{
 		internal NumberType type;
 
-		readonly Runtime runtime;
+		internal Runtime runtime;
 		readonly private float number;
 		readonly private int operand;
 
@@ -90,6 +90,6 @@ namespace SuperBASIC
 		}
 
 		public static implicit operator float(BasicNumber v) => v.GetValue();
-		public override string ToString() => $"{number}";
+		public override string ToString() => $"{GetValue()}";
 	}
 }

Functions/Goto.cs

@@ -0,0 +1,26 @@
+using System;
+using System.Collections.Generic;
+using System.Text;
+
+namespace SuperBASIC.Functions
+{
+	class Goto : IFunction
+	{
+		public float Apply(List<BasicNumber> arguments)
+		{
+			// Substract its own arity +1
+			arguments[0].runtime.pc = (int)arguments[0].GetOperand() - 2;
+			return 0f;
+		}
+	}
+	class JumpZero : IFunction
+	{
+		public float Apply(List<BasicNumber> arguments)
+		{
+			if(arguments[0] == 0)
+				// Substract its own arity +1
+				arguments[1].runtime.pc = (int)arguments[1].GetOperand() - 3;
+			return 0f;
+		}
+	}
+}

Parser.cs

@@ -28,43 +28,25 @@ namespace SuperBASIC
 			library = rt.lib;
 		}
 
-		public Bytecode ParseFile(string filepath)
+		internal enum Controls
 		{
-			Bytecode c = new Bytecode();
-			string[] sourceLines = File.ReadAllLines(filepath);
-			Regex lws = new Regex(@"\s+");
-			Regex leadings = new Regex(@"^\s+");
-			Regex trailings = new Regex(@"\s+$");
-			List<string> codeLines = new List<string>();
-			List<int> lineSpans = new List<int>();
-
-			int a = 0;
-			foreach (string line in sourceLines)
-			{
-				a++;
-				string l = lws.Replace(line, " ");
-				l = leadings.Replace(l, "");
-				l = trailings.Replace(l, "");
+			If, Then, Else, EndIf,
+			For, To, Step, Next,
+			While, Wend,
+			Repeat, Until,
+			Do, LoopCond
+		}
 
-				if (l != String.Empty)
-				{
-					lineSpans.Add(a);
-					a = 0;
-					codeLines.Add(l);
-				}
-			}
+		internal struct FlowControlTag
+		{
+			public Controls ctrl;
+			public int index;
+		}
 
-			for (int idx = 0; idx < codeLines.Count; idx++)
+		private void ParseExpression(Bytecode c, string[] components, int idx, List<int> lineSpans)
+		{
+			if (library.nameResolution.ContainsKey(components[0]))
 			{
-				string line = codeLines[idx];
-				var components = line.Split(' ');
-
-				if (!library.nameResolution.ContainsKey(components[0]))
-				{
-					int lineIndex = 0;
-					foreach (int cnt in lineSpans.GetRange(0, idx + 1)) lineIndex += cnt;
-					throw new ParseException($"Unknown operation \"{components[0]}\"\n\tat line {lineIndex}");
-				}
 
 				int opcode = library.nameResolution[components[0]];
 				int arity = library.arities[opcode];
@@ -117,7 +99,122 @@ namespace SuperBASIC
 					}
 				}
 			}
+			else
+			{
+				int lineIndex = 0;
+				foreach (int cnt in lineSpans.GetRange(0, idx + 1)) lineIndex += cnt;
+				throw new ParseException($"Unknown operation \"{components[0]}\"\n\tat line {lineIndex}");
+			}
+		}
+
+		public Bytecode ParseFile(string filepath)
+		{
+			Bytecode c = new Bytecode();
+			string[] sourceLines = File.ReadAllLines(filepath);
+			Regex lws = new Regex(@"\s+");
+			Regex leadings = new Regex(@"^\s+");
+			Regex trailings = new Regex(@"\s+$");
+			List<string> codeLines = new List<string>();
+			List<int> lineSpans = new List<int>();
+			Stack<FlowControlTag> labelStack = new Stack<FlowControlTag>();
+
+			int a = 0;
+			foreach (string line in sourceLines)
+			{
+				a++;
+				string l = lws.Replace(line, " ");
+				l = leadings.Replace(l, "");
+				l = trailings.Replace(l, "");
+
+				if (l != String.Empty)
+				{
+					lineSpans.Add(a);
+					a = 0;
+					codeLines.Add(l);
+				}
+			}
+
+			for (int idx = 0; idx < codeLines.Count; idx++)
+			{
+				string line = codeLines[idx];
+				var components = line.Split(' ');
 
+				var label = new FlowControlTag();
+				switch (components[0])
+				{
+					case "IF":
+						// Role: manages the expression
+						label.ctrl = Controls.If;
+						label.index = c.bytecode.Count;
+						labelStack.Push(label);
+						ParseExpression(c, components[1..], idx, lineSpans);
+						break;
+					case "THEN":
+						// Role: Jumps to the far block if false
+						// 1. Adds the label to update the destination
+						label.ctrl = Controls.Then;
+						label.index = c.bytecode.Count;
+						labelStack.Push(label);
+						// 2. Adds the jumper
+						c.bytecode.Add(new BasicNumber(runtime, library.nameResolution["JZ"]));
+						c.bytecode.Add(new BasicNumber(runtime));
+						c.bytecode.Add(new BasicNumber(runtime, 0f));
+						break;
+					case "ELSE":
+						//Role: skips its section if encountered, marks the THEN for JZ
+						//1. Gets the THEN label
+						label = labelStack.Pop();
+						if(label.ctrl != Controls.Then)
+						{
+							int lineIndex = 0;
+							foreach (int cnt in lineSpans.GetRange(0, idx + 1)) lineIndex += cnt;
+							throw new ParseException($"Orphaned ELSE\n\tat line {lineIndex}");
+						}
+						//2. Self tags for the ENDIF to complete the GOTO
+						var label_self = new FlowControlTag
+						{
+							ctrl = Controls.Else,
+							index = c.bytecode.Count
+						};
+						labelStack.Push(label_self);
+						//3. Pushes the GOTO
+						c.bytecode.Add(new BasicNumber(runtime, library.nameResolution["GOTO"]));
+						c.bytecode.Add(new BasicNumber(runtime, 0f));
+						//4. Place the THEN destination after the GOTO
+						c.bytecode[label.index+2] = new BasicNumber(runtime, c.bytecode.Count);
+						break;
+					case "ENDIF":
+						//Role: Destination if depending on what is skipped
+						label = labelStack.Pop();
+						if (label.ctrl == Controls.Else)
+						{
+							//Case 1: update the GOTO
+							c.bytecode[label.index + 1] = new BasicNumber(runtime, c.bytecode.Count);
+						}
+						else if (label.ctrl == Controls.Then)
+						{
+							//Case 2: update the JZ
+							c.bytecode[label.index + 2] = new BasicNumber(runtime, c.bytecode.Count);
+						} 
+						else 
+						{ 
+							int lineIndex = 0;
+							foreach (int cnt in lineSpans.GetRange(0, idx + 1)) lineIndex += cnt;
+							throw new ParseException($"Orphaned ENDIF\n\tat line {lineIndex}");
+						}
+						// Controls the syntax
+						if (labelStack.Pop().ctrl != Controls.If)
+						{
+							int lineIndex = 0;
+							foreach (int cnt in lineSpans.GetRange(0, idx + 1)) lineIndex += cnt;
+							throw new ParseException($"Orphaned ENDIF despite THEN\n\tat line {lineIndex}");
+						}
+						break;
+					default:
+						ParseExpression(c, components, idx, lineSpans);
+					break;
+				}
+			}
 			return c;
 		}
 	}

Program.cs

@@ -17,6 +17,8 @@ namespace SuperBASIC
 				lib.AddFunction(new Functions.Print(), 1, "PRINT");
 				lib.AddFunction(new Functions.Multiply(), 2, "MULTIPLY");
 				lib.AddFunction(new Functions.Compare(), 2, "COMPARE");
+				lib.AddFunction(new Functions.JumpZero(), 2, "JZ");
+				lib.AddFunction(new Functions.Goto(), 1, "GOTO");
 				lib.AddFunction(new Functions.Pi(), 0, "PI");
 				lib.AddFunction(new Functions.Euler(), 0, "EULER");
 				Runtime r = new Runtime(lib);

Runtime.cs

@@ -9,6 +9,7 @@ namespace SuperBASIC
 		float register;
 		internal Library lib;
 		Bytecode code;
+		internal int pc = 0;
 
 		public Runtime(Library library)
 		{
@@ -22,14 +23,14 @@ namespace SuperBASIC
 
 		public void Run()
 		{
-			for(kt">int idx = 0; idx < code.bytecode.Count;)
+			for(n">pc = 0; pc < code.bytecode.Count;)
 			{
-				int opcode = code.bytecode[idx].GetOperand();
+				int opcode = code.bytecode[pc].GetOperand();
 				int arity = lib.arities[opcode];
 				IFunction op = lib.functions[opcode];
-				var args = code.bytecode.GetRange(idx + 1, arity);
+				var args = code.bytecode.GetRange(pc + 1, arity);
 				SetRegister(op.Apply(args));
-				idx += arity + 1;
+				pc += arity + 1;
 			}
 		}
 

Test.basic

@@ -1,4 +1,9 @@
 EULER
 MULTIPLY $ $
-COMPARE $ 7.3890557
-PRINT $
+
+IF COMPARE $ 7.3890557
+THEN
+PRINT 25
+ELSE
+PRINT 10
+ENDIF