From 3066ba9032f8e538698ae4685d81bdf1490e9cf8 Mon Sep 17 00:00:00 2001
From: Moritz Gmeiner <moritz@gmeiner.net>
Date: Sun, 1 Sep 2024 20:46:49 +0200
Subject: [PATCH] split off declarations from statements

added error for duplicate parameter names
---
 frontend/src/parser/_parser.rs | 28 ++++++++++++++++++++++------
 frontend/src/parser/error.rs   |  2 ++
 2 files changed, 24 insertions(+), 6 deletions(-)

diff --git a/frontend/src/parser/_parser.rs b/frontend/src/parser/_parser.rs
index 8f4558c..a0eeba6 100644
--- a/frontend/src/parser/_parser.rs
+++ b/frontend/src/parser/_parser.rs
@@ -102,7 +102,7 @@ impl Parser {
 
         while !me.token_iter.is_empty() && me.peek_token().token_type != TokenType::EOF {
             // statements.push(me.statement()?);
-            match me.statement() {
+            match me.declaration() {
                 Ok(stmt) => {
                     statements.push(stmt);
                 }
@@ -167,15 +167,21 @@ impl Parser {
         }
     }
 
+    fn declaration(&mut self) -> ParserResult<Stmt> {
+        match self.peek_token().token_type {
+            TokenType::Var => self.var_declaration(),
+            TokenType::Class => self.class_declaration(),
+            TokenType::Fun => self.fun_declaration(),
+            _ => self.statement(),
+        }
+    }
+
     fn statement(&mut self) -> ParserResult<Stmt> {
         match self.peek_token().token_type {
             TokenType::Print => self.print_statement(),
             TokenType::If => self.if_statement(),
             TokenType::While => self.while_statement(),
             TokenType::For => self.for_statement(),
-            TokenType::Var => self.var_declaration(),
-            TokenType::Class => self.class_declaration(),
-            TokenType::Fun => self.fun_declaration(),
             TokenType::LeftBrace => self.block(),
             TokenType::Break => {
                 let code_pos = self.peek_token().code_pos;
@@ -491,7 +497,17 @@ impl Parser {
         while self.peek_token().token_type == TokenType::Comma {
             assert_eq!(self.next_token().token_type, TokenType::Comma);
 
-            param_names.push(self.identifier("Expected parameter name")?);
+            let code_pos = self.peek_token().code_pos;
+
+            let name = self.identifier("Expected parameter name")?;
+
+            for param in param_names.iter() {
+                if &name == param {
+                    return Err(ParserError::DuplicateParameterName { code_pos });
+                }
+            }
+
+            param_names.push(name);
         }
 
         self.consume_token(TokenType::RightParen, |token| {
@@ -510,7 +526,7 @@ impl Parser {
         let mut statements = Vec::new();
 
         while self.peek_token().token_type != TokenType::RightBrace {
-            let statement = self.statement().map_err(|err| {
+            let statement = self.declaration().map_err(|err| {
                 if self.peek_token().token_type == TokenType::EOF {
                     ParserError::MissingRightBrace {
                         code_pos: self.peek_token().code_pos,
diff --git a/frontend/src/parser/error.rs b/frontend/src/parser/error.rs
index a801790..49ab93b 100644
--- a/frontend/src/parser/error.rs
+++ b/frontend/src/parser/error.rs
@@ -46,4 +46,6 @@ pub enum ParserError {
     ReturnInInit { code_pos: CodePos },
     #[error("ParserError: Missing method name after super")]
     MissingMethodAfterSuper { code_pos: CodePos },
+    #[error("ParserError: duplicate parameter name at {code_pos}")]
+    DuplicateParameterName { code_pos: CodePos },
 }