Add counter variable to for statement.

CHANGELOG.md

@@ -17,6 +17,7 @@ Breaking changes
 New features
 ------------
 
+* New syntax for `for` statement to include counter variable.
 * An integer value can now be indexed to get/set a single bit.
 * The `bits` method of an integer can be used to iterate through its bits.
 

src/ast.rs

@@ -944,8 +944,8 @@ pub enum Stmt {
     While(Expr, Box<StmtBlock>, Position),
     /// `do` `{` stmt `}` `while`|`until` expr
     Do(Box<StmtBlock>, Expr, bool, Position),
-    /// `for` id `in` expr `{` stmt `}`
+    /// `for` `(` id `,` counter `)` `in` expr `{` stmt `}`
-    For(Expr, Box<(Ident, StmtBlock)>, Position),
+    For(Expr, Box<(Ident, Option<Ident>, StmtBlock)>, Position),
     /// \[`export`\] `let` id `=` expr
     Let(Expr, Box<Ident>, bool, Position),
     /// \[`export`\] `const` id `=` expr
@@ -1166,7 +1166,7 @@ impl Stmt {
             Self::While(condition, block, _) | Self::Do(block, condition, _, _) => {
                 condition.is_pure() && block.0.iter().all(Stmt::is_pure)
             }
-            Self::For(iterable, x, _) => iterable.is_pure() && (x.1).0.iter().all(Stmt::is_pure),
+            Self::For(iterable, x, _) => iterable.is_pure() && (x.2).0.iter().all(Stmt::is_pure),
             Self::Let(_, _, _, _)
             | Self::Const(_, _, _, _)
             | Self::Assignment(_, _)
@@ -1286,7 +1286,7 @@ impl Stmt {
                 if !e.walk(path, on_node) {
                     return false;
                 }
-                for s in &(x.1).0 {
+                for s in &(x.2).0 {
                     if !s.walk(path, on_node) {
                         return false;
                     }
@@ -1777,7 +1777,7 @@ impl fmt::Debug for Expr {
                 }
                 f.write_str(&x.2)?;
                 match i.map_or_else(|| x.0, |n| NonZeroUsize::new(n.get() as usize)) {
-                    Some(n) => write!(f, ", {}", n)?,
+                    Some(n) => write!(f, " #{}", n)?,
                     _ => (),
                 }
                 f.write_str(")")

src/engine.rs

@@ -14,7 +14,7 @@ use crate::token::Token;
 use crate::utils::get_hasher;
 use crate::{
     Dynamic, EvalAltResult, Identifier, ImmutableString, Module, Position, RhaiResult, Scope,
-    Shared, StaticVec,
+    Shared, StaticVec, INT,
 };
 #[cfg(feature = "no_std")]
 use std::prelude::v1::*;
@@ -2521,7 +2521,7 @@ impl Engine {
 
             // For loop
             Stmt::For(expr, x, _) => {
-                let (Ident { name, .. }, statements) = x.as_ref();
+                let (Ident { name, .. }, counter, statements) = x.as_ref();
                 let iter_obj = self
                     .eval_expr(scope, mods, state, lib, this_ptr, expr, level)?
                     .flatten();
@@ -2550,17 +2550,40 @@ impl Engine {
                     });
 
                 if let Some(func) = func {
-                    // Add the loop variable
+                    // Add the loop variables
-                    let var_name: Cow<'_, str> = if state.is_global() {
+                    let orig_scope_len = scope.len();
-                        name.to_string().into()
+                    let counter_index = if let Some(Ident { name, .. }) = counter {
+                        scope.push(unsafe_cast_var_name_to_lifetime(name), 0 as INT);
+                        Some(scope.len() - 1)
                     } else {
-                        unsafe_cast_var_name_to_lifetime(name).into()
+                        None
                     };
-                    scope.push(var_name, ());
+                    scope.push(unsafe_cast_var_name_to_lifetime(name), ());
                     let index = scope.len() - 1;
                     state.scope_level += 1;
 
-                    for iter_value in func(iter_obj) {
+                    for (x, iter_value) in func(iter_obj).enumerate() {
+                        // Increment counter
+                        if let Some(c) = counter_index {
+                            #[cfg(not(feature = "unchecked"))]
+                            if x > INT::MAX as usize {
+                                return EvalAltResult::ErrorArithmetic(
+                                    format!("for-loop counter overflow: {}", x),
+                                    counter
+                                        .as_ref()
+                                        .expect("never fails because `counter` is `Some`")
+                                        .pos,
+                                )
+                                .into();
+                            }
+
+                            let mut counter_var = scope
+                                .get_mut_by_index(c)
+                                .write_lock::<INT>()
+                                .expect("never fails because the counter always holds an `INT`");
+                            *counter_var = x as INT;
+                        }
+
                         let loop_var = scope.get_mut_by_index(index);
                         let value = iter_value.flatten();
 
@@ -2600,7 +2623,7 @@ impl Engine {
                     }
 
                     state.scope_level -= 1;
-                    scope.rewind(scope.len() - 1);
+                    scope.rewind(orig_scope_len);
                     Ok(Dynamic::UNIT)
                 } else {
                     EvalAltResult::ErrorFor(expr.position()).into()
@@ -2672,8 +2695,6 @@ impl Engine {
                             }
                             #[cfg(not(feature = "no_object"))]
                             _ => {
-                                use crate::INT;
-
                                 let mut err_map: Map = Default::default();
                                 let err_pos = err.take_position();
 

src/optimize.rs

@@ -594,8 +594,8 @@ fn optimize_stmt(stmt: &mut Stmt, state: &mut State, preserve_result: bool) {
         // for id in expr { block }
         Stmt::For(iterable, x, _) => {
             optimize_expr(iterable, state, false);
-            let body = mem::take(x.1.statements()).into_vec();
+            let body = mem::take(x.2.statements()).into_vec();
-            *x.1.statements() = optimize_stmt_block(body, state, false, true, false).into();
+            *x.2.statements() = optimize_stmt_block(body, state, false, true, false).into();
         }
         // let id = expr;
         Stmt::Let(expr, _, _, _) => optimize_expr(expr, state, false),

src/parse_error.rs

@@ -116,6 +116,8 @@ pub enum ParseErrorType {
     DuplicatedProperty(String),
     /// A `switch` case is duplicated.
     DuplicatedSwitchCase,
+    /// A variable name is duplicated. Wrapped value is the variable name.
+    DuplicatedVariable(String),
     /// The default case of a `switch` statement is not the last.
     WrongSwitchDefaultCase,
     /// The case condition of a `switch` statement is not appropriate.
@@ -200,6 +202,7 @@ impl ParseErrorType {
             Self::MalformedCapture(_) => "Invalid capturing",
             Self::DuplicatedProperty(_) => "Duplicated property in object map literal",
             Self::DuplicatedSwitchCase => "Duplicated switch case",
+            Self::DuplicatedVariable(_) => "Duplicated variable name",
             Self::WrongSwitchDefaultCase => "Default switch case is not the last",
             Self::WrongSwitchCaseCondition => "Default switch case cannot have condition",
             Self::PropertyExpected => "Expecting name of a property",
@@ -247,6 +250,7 @@ impl fmt::Display for ParseErrorType {
                 write!(f, "Duplicated property '{}' for object map literal", s)
             }
             Self::DuplicatedSwitchCase => f.write_str(self.desc()),
+            Self::DuplicatedVariable(s) => write!(f, "Duplicated variable name '{}'", s),
 
             Self::ExprExpected(s) => write!(f, "Expecting {} expression", s),
 

src/parser.rs

@@ -2144,6 +2144,21 @@ fn parse_for(
     lib: &mut FunctionsLib,
     mut settings: ParseSettings,
 ) -> Result<Stmt, ParseError> {
+    fn get_name_pos(input: &mut TokenStream) -> Result<(String, Position), ParseError> {
+        match input.next().expect(NEVER_ENDS) {
+            // Variable name
+            (Token::Identifier(s), pos) => Ok((s, pos)),
+            // Reserved keyword
+            (Token::Reserved(s), pos) if is_valid_identifier(s.chars()) => {
+                Err(PERR::Reserved(s).into_err(pos))
+            }
+            // Bad identifier
+            (Token::LexError(err), pos) => Err(err.into_err(pos)),
+            // Not a variable name
+            (_, pos) => Err(PERR::VariableExpected.into_err(pos)),
+        }
+    }
+
     #[cfg(not(feature = "unchecked"))]
     settings.ensure_level_within_max_limit(state.max_expr_depth)?;
 
@@ -2151,17 +2166,36 @@ fn parse_for(
     settings.pos = eat_token(input, Token::For);
 
     // for name ...
-    let (name, name_pos) = match input.next().expect(NEVER_ENDS) {
+    let (name, name_pos, counter_name, counter_pos) = if match_token(input, Token::LeftParen).0 {
-        // Variable name
+        // ( name, counter )
-        (Token::Identifier(s), pos) => (s, pos),
+        let (name, name_pos) = get_name_pos(input)?;
-        // Reserved keyword
+        let (has_comma, pos) = match_token(input, Token::Comma);
-        (Token::Reserved(s), pos) if is_valid_identifier(s.chars()) => {
+        if !has_comma {
-            return Err(PERR::Reserved(s).into_err(pos));
+            return Err(PERR::MissingToken(
+                Token::Comma.into(),
+                "after the iteration variable name".into(),
+            )
+            .into_err(pos));
         }
-        // Bad identifier
+        let (counter_name, counter_pos) = get_name_pos(input)?;
-        (Token::LexError(err), pos) => return Err(err.into_err(pos)),
+
-        // Not a variable name
+        if counter_name == name {
-        (_, pos) => return Err(PERR::VariableExpected.into_err(pos)),
+            return Err(PERR::DuplicatedVariable(counter_name).into_err(counter_pos));
+        }
+
+        let (has_close_paren, pos) = match_token(input, Token::RightParen);
+        if !has_close_paren {
+            return Err(PERR::MissingToken(
+                Token::RightParen.into(),
+                "to close the iteration variable".into(),
+            )
+            .into_err(pos));
+        }
+        (name, name_pos, Some(counter_name), Some(counter_pos))
+    } else {
+        // name
+        let (name, name_pos) = get_name_pos(input)?;
+        (name, name_pos, None, None)
     };
 
     // for name in ...
@@ -2180,8 +2214,18 @@ fn parse_for(
     ensure_not_statement_expr(input, "a boolean")?;
     let expr = parse_expr(input, state, lib, settings.level_up())?;
 
-    let loop_var = state.get_identifier(name);
     let prev_stack_len = state.stack.len();
+
+    let counter_var = if let Some(name) = counter_name {
+        let counter_var = state.get_identifier(name);
+        state
+            .stack
+            .push((counter_var.clone(), AccessMode::ReadWrite));
+        Some(counter_var)
+    } else {
+        None
+    };
+    let loop_var = state.get_identifier(name);
     state.stack.push((loop_var.clone(), AccessMode::ReadWrite));
 
     settings.is_breakable = true;
@@ -2196,6 +2240,10 @@ fn parse_for(
                 name: loop_var,
                 pos: name_pos,
             },
+            counter_var.map(|name| Ident {
+                name,
+                pos: counter_pos.expect("never fails because `counter_var` is `Some`"),
+            }),
             body.into(),
         )),
         settings.pos,
@@ -2342,10 +2390,19 @@ fn parse_export(
 
         let rename = if match_token(input, Token::As).0 {
             match input.next().expect(NEVER_ENDS) {
-                (Token::Identifier(s), pos) => Some(Ident {
+                (Token::Identifier(s), pos) => {
+                    if exports.iter().any(|(_, alias)| match alias {
+                        Some(Ident { name, .. }) if name == &s => true,
+                        _ => false,
+                    }) {
+                        return Err(PERR::DuplicatedVariable(s).into_err(pos));
+                    }
+
+                    Some(Ident {
                         name: state.get_identifier(s),
                         pos,
-                }),
+                    })
+                }
                 (Token::Reserved(s), pos) if is_valid_identifier(s.chars()) => {
                     return Err(PERR::Reserved(s).into_err(pos));
                 }

tests/for.rs

@@ -37,6 +37,22 @@ fn test_for_loop() -> Result<(), Box<EvalAltResult>> {
         35
     );
 
+    #[cfg(not(feature = "no_index"))]
+    assert_eq!(
+        engine.eval::<INT>(
+            "
+                let sum = 0;
+                let inputs = [1, 2, 3, 4, 5];
+
+                for (x, i) in inputs {
+                    sum += x * (i + 1);
+                }
+                sum
+            "
+        )?,
+        55
+    );
+
     assert_eq!(
         engine.eval::<INT>(
             "