Further attempts at refactoring the error handling code

* Everything's still broken though

src/errors.rs

@@ -38,7 +38,7 @@ impl fmt::Display for ErrorKind {
 #[derive(Debug, Clone)]
 pub struct SloxError {
     kind: ErrorKind,
-    line: usize,
+    line: Option<usize>,
     pos: String,
     message: String,
 }
@@ -51,10 +51,10 @@ impl SloxError {
     pub fn scanner_error(line: usize, ch: Option<char>, message: String) -> Self {
         Self {
             kind: ErrorKind::Scan,
-            line,
+            line: Some(line),
             pos: match ch {
-                None => "at end of input".to_owned(),
+                None => " at end of input".to_owned(),
-                Some(ch) => format!("near {:?}", ch)
+                Some(ch) => format!(" near {:?}", ch),
             },
             message,
         }
@@ -64,25 +64,44 @@ impl SloxError {
     pub fn with_token(kind: ErrorKind, token: &Token, message: String) -> Self {
         Self {
             kind,
-            line: token.line,
+            line: Some(token.line),
             pos: if token.token_type == TokenType::Eof {
-                "at end of input".to_owned()
+                " at end of input".to_owned()
             } else {
-                format!("near '{}'", token.lexeme)
+                format!(" near '{}'", token.lexeme)
             },
             message,
         }
     }
+
+    /// Create an error indicating a stage failed.
+    fn stage_failed(kind: ErrorKind) -> Self {
+        Self {
+            kind,
+            line: None,
+            pos: "".to_owned(),
+            message: "exiting...".to_owned(),
+        }
+    }
+
+    /// Return the type of error
+    pub fn kind(&self) -> &ErrorKind {
+        &self.kind
+    }
 }
 
 impl Error for SloxError {}
 
 impl Display for SloxError {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        let line = match self.line {
+            None => "".to_owned(),
+            Some(l) => format!("[line {}] ", l),
+        };
         write!(
             f,
-            "[line {}] {} error {}: {}",
+            "{}{} error{}: {}",
-            self.line, self.kind, self.pos, self.message
+            line, self.kind, self.pos, self.message
         )
     }
 }
@@ -102,9 +121,32 @@ impl ErrorHandler {
 
     /// Report an error.
     pub fn report(&mut self, error: SloxError) {
-        if self.had_error.is_none() {
         self.had_error = Some(error.kind);
-        }
         println!("{error}");
     }
+
+    /// Transmit the last value returned by some component, or report its error
+    /// and generate the final error.
+    pub fn report_or_continue<T>(&mut self, result: SloxResult<T>) -> SloxResult<T> {
+        match result {
+            Ok(v) => Ok(v),
+            Err(e) => {
+                self.report(e);
+                let fe = SloxError::stage_failed(e.kind);
+                println!("{fe}");
+                Err(fe)
+            }
+        }
+    }
+
+    /// Generate an error that corresponds to the last error encountered.
+    pub fn final_error<T>(&self, result: T) -> SloxResult<T> {
+        if let Some(err_kind) = self.had_error {
+            let err = SloxError::stage_failed(err_kind);
+            println!("{err}");
+            Err(err)
+        } else {
+            Ok(result)
+        }
+    }
 }

src/interpreter/interpretable.rs

@@ -2,21 +2,26 @@ use std::{cell::RefCell, rc::Rc};
 
 use crate::{
     ast,
-    errors::{ErrorHandler, InterpreterError},
+    errors::{ErrorHandler, SloxError},
     interpreter::{Environment, EnvironmentRef, Value},
+    resolver::ResolvedVariables,
     tokens::{Token, TokenType},
 };
 
 use super::functions::Function;
 
 /// Evaluate an interpretable, returning its value.
-pub fn evaluate(err_hdl: &mut ErrorHandler, ast: &dyn Interpretable) -> Option<Value> {
+pub fn evaluate(
+    err_hdl: &mut ErrorHandler,
+    ast: &dyn Interpretable,
+    vars: ResolvedVariables,
+) -> Result<Value, SloxError> {
     let env = Rc::new(RefCell::new(Environment::default()));
     match ast.interpret(&env) {
-        Ok(v) => Some(v.result()),
+        Ok(v) => Ok(v.result()),
         Err(e) => {
-            e.report(err_hdl);
+            err_hdl.report(e);
-            None
+            Err(e)
         }
     }
 }
@@ -65,7 +70,7 @@ impl From<Value> for InterpreterFlowControl {
 }
 
 /// A result returned by some part of the interpreter.
-pub type InterpreterResult = Result<InterpreterFlowControl, InterpreterError>;
+pub type InterpreterResult = Result<InterpreterFlowControl, SloxError>;
 
 /// An Interpretable can be evaluated and will return a value.
 pub trait Interpretable {
@@ -326,12 +331,12 @@ impl ast::ExprNode {
             TokenType::Plus => match (left_value, right_value) {
                 (Value::Number(a), Value::Number(b)) => Ok(Value::Number(a + b).into()),
                 (Value::String(a), Value::String(b)) => Ok(Value::String(a + &b).into()),
-                _ => Err(InterpreterError::new(operator, "type error")),
+                _ => Err(SloxError::new(operator, "type error")),
             },
 
             TokenType::Minus => match (left_value, right_value) {
                 (Value::Number(a), Value::Number(b)) => Ok(Value::Number(a - b).into()),
-                _ => Err(InterpreterError::new(operator, "type error")),
+                _ => Err(SloxError::new(operator, "type error")),
             },
 
             TokenType::Star => match (left_value, right_value) {
@@ -339,38 +344,38 @@ impl ast::ExprNode {
                 (Value::String(a), Value::Number(b)) => {
                     Ok(Value::String(a.repeat(b as usize)).into())
                 }
-                _ => Err(InterpreterError::new(operator, "type error")),
+                _ => Err(SloxError::new(operator, "type error")),
             },
 
             TokenType::Slash => match (left_value, right_value) {
                 (Value::Number(a), Value::Number(b)) => {
                     if b == 0. {
-                        Err(InterpreterError::new(operator, "division by zero"))
+                        Err(SloxError::new(operator, "division by zero"))
                     } else {
                         Ok(Value::Number(a / b).into())
                     }
                 }
-                _ => Err(InterpreterError::new(operator, "type error")),
+                _ => Err(SloxError::new(operator, "type error")),
             },
 
             TokenType::Greater => match (left_value, right_value) {
                 (Value::Number(a), Value::Number(b)) => Ok(Value::Boolean(a > b).into()),
-                _ => Err(InterpreterError::new(operator, "type error")),
+                _ => Err(SloxError::new(operator, "type error")),
             },
 
             TokenType::GreaterEqual => match (left_value, right_value) {
                 (Value::Number(a), Value::Number(b)) => Ok(Value::Boolean(a >= b).into()),
-                _ => Err(InterpreterError::new(operator, "type error")),
+                _ => Err(SloxError::new(operator, "type error")),
             },
 
             TokenType::Less => match (left_value, right_value) {
                 (Value::Number(a), Value::Number(b)) => Ok(Value::Boolean(a < b).into()),
-                _ => Err(InterpreterError::new(operator, "type error")),
+                _ => Err(SloxError::new(operator, "type error")),
             },
 
             TokenType::LessEqual => match (left_value, right_value) {
                 (Value::Number(a), Value::Number(b)) => Ok(Value::Boolean(a <= b).into()),
-                _ => Err(InterpreterError::new(operator, "type error")),
+                _ => Err(SloxError::new(operator, "type error")),
             },
 
             TokenType::EqualEqual => Ok(Value::Boolean(left_value == right_value).into()),
@@ -396,7 +401,7 @@ impl ast::ExprNode {
                 if let Value::Number(n) = right_value {
                     Ok(Value::Number(-n).into())
                 } else {
-                    Err(InterpreterError::new(operator, "number expected"))
+                    Err(SloxError::new(operator, "number expected"))
                 }
             }
 
@@ -441,7 +446,7 @@ impl ast::ExprNode {
         if let Value::Callable(callable_ref) = &callee {
             let callable = callable_ref.borrow();
             if callable.arity() != arg_values.len() {
-                Err(InterpreterError::new(
+                Err(SloxError::new(
                     right_paren,
                     &format!(
                         "expected {} arguments, found {}",
@@ -453,7 +458,7 @@ impl ast::ExprNode {
                 Ok(callable.call(environment, arg_values)?.into())
             }
         } else {
-            Err(InterpreterError::new(
+            Err(SloxError::new(
                 right_paren,
                 "can only call functions and classes",
             ))

src/main.rs

@@ -14,34 +14,32 @@ use std::{
 
 #[cfg(feature = "dump_ast")]
 use ast::AstDumper;
-use errors::{ErrorHandler, ErrorType};
+use errors::{ErrorHandler, SloxResult};
 use interpreter::evaluate;
 use parser::Parser;
+use resolver::resolve_variables;
 use scanner::Scanner;
 
 /// Execute a script.
-fn run(source: String) -> ErrorHandler {
+fn run(source: String) -> SloxResult<()> {
     let mut error_handler = ErrorHandler::default();
 
     let scanner = Scanner::new(source);
-    let tokens = scanner.scan_tokens(&mut error_handler);
+    let tokens = scanner.scan_tokens(&mut error_handler)?;
-
     #[cfg(feature = "dump_tokens")]
     for token in tokens.iter() {
         println!("{:#?}", token);
     }
 
     let parser = Parser::new(tokens);
-    match parser.parse(&mut error_handler) {
+    let ast = parser.parse(&mut error_handler)?;
-        None => (),
-        Some(ast) => {
     #[cfg(feature = "dump_ast")]
     println!("AST generated ! {}", ast.dump());
-            evaluate(&mut error_handler, &ast);
-        }
-    }
 
-    error_handler
+    let resolved_vars = error_handler.final_error(resolve_variables(&ast))?;
+    error_handler.final_error(evaluate(&ast, resolved_vars));
+
+    Ok(())
 }
 
 /// Run the REPL.
@@ -64,7 +62,7 @@ fn run_prompt() {
 }
 
 /// Load a file and run the script it contains.
-fn run_file(file: &str) -> ErrorHandler {
+fn run_file(file: &str) -> SloxResult<()> {
     let contents = fs::read_to_string(file).unwrap_or_else(|_| panic!("Could not load {}", file));
     run(contents)
 }
@@ -77,10 +75,9 @@ fn main() -> Result<(), ExitCode> {
         run_prompt();
         Ok(())
     } else if n_args == 1 {
-        match run_file(&args[0]).had_error() {
+        match run_file(&args[0]) {
-            None => Ok(()),
+            Ok(()) => Ok(()),
-            Some(ErrorType::Parse) => Err(ExitCode::from(65)),
+            Err(err) => Err(ExitCode::from(err.kind().exit_code())),
-            Some(ErrorType::Runtime) => Err(ExitCode::from(70)),
         }
     } else {
         println!("Usage: slox [script]");

src/parser.rs

@@ -74,11 +74,11 @@ impl Parser {
 
     /// Parse the tokens into an AST and return it, or return nothing if a
     /// parser error occurs.
-    pub fn parse(mut self, err_hdl: &mut ErrorHandler) -> Option<ast::ProgramNode> {
+    pub fn parse(mut self, err_hdl: &mut ErrorHandler) -> SloxResult<ast::ProgramNode> {
         self.loop_state.push(LoopParsingState::None);
         let result = self.parse_program(err_hdl);
         self.loop_state.pop();
-        result
+        err_hdl.final_error(result)
     }
 
     /// Synchronize the parser after an error.
@@ -111,7 +111,7 @@ impl Parser {
     /// ```
     /// program := statement*
     /// ```
-    fn parse_program(&mut self, err_hdl: &mut ErrorHandler) -> Option<ast::ProgramNode> {
+    fn parse_program(&mut self, err_hdl: &mut ErrorHandler) -> ast::ProgramNode {
         let mut stmts: Vec<ast::StmtNode> = Vec::new();
         while !self.is_at_end() {
             match self.parse_statement() {
@@ -122,11 +122,7 @@ impl Parser {
                 }
             }
         }
-        if err_hdl.had_error().is_none() {
+        ast::ProgramNode(stmts)
-            Some(ast::ProgramNode(stmts))
-        } else {
-            None
-        }
     }
 
     /// Parse the following rule:

src/resolver.rs

@@ -8,7 +8,7 @@ use crate::{
 
 pub type ResolvedVariables = HashMap<*const ast::ExprNode, usize>;
 
-pub fn resolve_variables(program: &ast::ProgramNode) -> Result<ResolvedVariables, SloxError> {
+pub fn resolve_variables(program: &ast::ProgramNode) -> SloxResult<ResolvedVariables> {
     let mut state = ResolverState::default();
     program.resolve(&mut state).map(|_| state.resolved)
 }

src/scanner.rs

@@ -60,7 +60,7 @@ impl Scanner {
 
     /// Scan the source code, generating the list of tokens and returning it.
     /// The scanner itself is destroyed once the process is complete.
-    pub fn scan_tokens(mut self, err_hdl: &mut ErrorHandler) -> Vec<Token> {
+    pub fn scan_tokens(mut self, err_hdl: &mut ErrorHandler) -> SloxResult<Vec<Token>> {
         while !self.is_at_end() {
             self.start = self.current;
             if let Err(e) = self.scan_token() {
@@ -72,7 +72,7 @@ impl Scanner {
             lexeme: String::from(""),
             line: self.line,
         });
-        self.tokens
+        err_hdl.final_error(self.tokens)
     }
 
     /// Read the next token from the input