ast: Implement let in expression and add a node for error at runtime

Author: hexaredecimal

src/main/java/org/piccode/ast/ErrorNodeExpr.java

@@ -1,45 +1,32 @@
 package org.piccode.ast;
 
 import org.piccode.piccodescript.TargetEnvironment;
+import org.piccode.rt.PiccodeException;
 import org.piccode.rt.PiccodeValue;
 
 /**
  *
  * @author hexaredecimal
  */
-public class Arg extends Ast {
-	public String name;
-	public Ast def_val;
-	public boolean export;
+public class ErrorNodeExpr extends Ast {
+	public String message;
 
-	public Arg(String name, Ast def_val) {
-		this.name = name;
-		this.def_val = def_val;
-		this.export = false;
+	public ErrorNodeExpr(String message) {
+		this.message = message;
 	}
-
-	public Arg(String name) {
-		this.name = name;
-		this.def_val = null;
-		this.export = false;
-	}
-
+	
 	@Override
-	public String toString() {
-		if (def_val == null) {
-			return name;
-		}
-		return name  + "=" + def_val;
+	public PiccodeValue execute(Integer frame) {
+		throw new PiccodeException(file, line, column, message);
 	}
 
 	@Override
-	public PiccodeValue execute(Integer frame) {
+	public String codeGen(TargetEnvironment target) {
 		throw new UnsupportedOperationException("Not supported yet."); // Generated from nbfs://nbhost/SystemFileSystem/Templates/Classes/Code/GeneratedMethodBody
 	}
 
 	@Override
-	public String codeGen(TargetEnvironment target) {
-		throw new UnsupportedOperationException("Not supported yet."); // Generated from nbfs://nbhost/SystemFileSystem/Templates/Classes/Code/GeneratedMethodBody
+	public String toString() {
+		return "ErrorExpr";
 	}
-	
 }

src/main/java/org/piccode/ast/LetInExprAst.java

@@ -1,65 +1,76 @@
 package org.piccode.ast;
 
 import java.util.List;
+import java.util.function.Function;
+import java.util.function.Supplier;
 import org.piccode.piccodescript.TargetEnvironment;
 import org.piccode.rt.Context;
 import org.piccode.rt.PiccodeBoolean;
+import org.piccode.rt.PiccodeException;
+import org.piccode.rt.PiccodeReturnException;
+import org.piccode.rt.PiccodeUnit;
 import org.piccode.rt.PiccodeValue;
 
 /**
  *
  * @author hexaredecimal
  */
-public class DoExprAst extends Ast {
-	public List<Ast> nodes; 
+public class LetInExprAst extends Ast {
 
-	public DoExprAst(List<Ast> nodes) {
-		this.nodes = nodes;
-	}
+	public List<Ast> vars;
+	public Ast expr;
 
+	public LetInExprAst(List<Ast> vars, Ast expr) {
+		this.vars = vars;
+		this.expr = expr;
+	}
 
 	@Override
 	public String toString() {
-		StringBuilder sb = new StringBuilder();
-		for (int i = 0; i < nodes.size(); i++) {
-			sb.append(nodes.get(i));
-			sb.append("\n");
+		var sb = new StringBuilder();
+		sb.append("let\n");
+		for (var decl : vars) {
+			sb.append(decl.toString().indent(4));
 		}
+		sb.append("in\n");
+		sb.append(expr.toString().indent(4));
 		return sb.toString();
 	}
 
 	@Override
 	public PiccodeValue execute(Integer frame) {
-		PiccodeValue result = null;
+		return evaluate(frame, () -> {
+			for (var decl : vars) {
+				decl.execute(frame);
+			}
+			return evaluate(frame, () -> expr.execute(frame));
+		});
+	}
+
+	private PiccodeValue evaluate(Integer frame, Supplier<PiccodeValue> fx) {
 		var ctx = frame == null
-			? Context.top
-			: Context.getContextAt(frame);
-		
+						? Context.top
+						: Context.getContextAt(frame);
 		ctx.pushScope();
-		for (var stmt: nodes) {
-			result = stmt.execute(frame);
+		try {
+			return fx.get();
+		} catch (PiccodeReturnException | PiccodeException e) {
+			ctx.dropScope();
+			throw e;
 		}
-		ctx.dropScope();
-		return result;
 	}
-
+	
 	@Override
 	public String codeGen(TargetEnvironment target) {
 		return switch (target) {
-			case JS -> codeGenJSDoExpr(target);
-			default -> "todo";
+			case JS ->
+				codeGenJSDoExpr(target);
+			default ->
+				"todo";
 		};
 	}
 
 	private String codeGenJSDoExpr(TargetEnvironment env) {
-		var sb = new StringBuilder()
-		.append("() => {\n");
-
-		nodes.forEach(node -> {
-			sb.append(node.codeGen(env)).append(";");
-		});
-		
-		sb.append("};\n");
-		return sb.toString();
+		return null;
 	}
 }

src/main/java/org/piccode/ast/PiccodeVisitor.java

@@ -23,6 +23,19 @@ public PiccodeVisitor(String file) {
 		fileName = file;
 	}
 
+	@Override
+	public Ast visitLet_decl(Let_declContext ctx) {
+		var tok = ctx.getStart();
+		List<Ast> vars = new ArrayList<>();
+		for (var decl: ctx.var_decl()) {
+			vars.add(visitVar_decl(decl));
+		}
+		var expr = visitExpr(ctx.expr());
+		var result = new LetInExprAst(vars, expr);
+		result.file = fileName;
+		return finalizeAstNode(result, tok);
+	}
+
 	@Override
 	public Ast visitVar_decl(Var_declContext var_decl) {
 		var tok = var_decl.ID().getSymbol();
@@ -269,6 +282,10 @@ public Ast visitExpr(ExprContext expr) {
 			return visitVar_decl(expr.var_decl());
 		}
 
+		if (expr.let_decl() != null) {
+			return visitLet_decl(expr.let_decl());
+		}
+
 		if (expr.closure_decl() != null) {
 			return visitClosure_decl(expr.closure_decl());
 		}