Precalculate stack positions for variables

- Parser calculates positions for the variables
- This removes the lookup time during runtime
- Consistent high performance

src/ast.rs

@@ -83,7 +83,7 @@ pub enum Expression {
     /// String literal
     String(Sid),
     /// Variable
-    Var(Sid),
+    Var(Sid, usize),
     /// Binary operation. Consists of type, left hand side and right hand side
     BinOp(BinOpType, Box<Expression>, Box<Expression>),
     /// Unary operation. Consists of type and operand

src/interpreter.rs

@@ -15,7 +15,7 @@ pub struct Interpreter {
     capture_output: bool,
     output: Vec<Value>,
     // Variable table stores the runtime values of variables
-    vartable: Vec<(Sid, Value)>,
+    vartable: Vec<Value>,
 
     stringstore: StringStore,
 }
@@ -33,20 +33,12 @@ impl Interpreter {
         &self.output
     }
 
-    fn get_var(&self, name: Sid) -> Option<Value> {
-        self.vartable
-            .iter()
-            .rev()
-            .find(|it| it.0 == name)
-            .map(|it| it.1.clone())
+    fn get_var(&self, idx: usize) -> Option<Value> {
+        self.vartable.get(idx).cloned()
     }
 
-    fn get_var_mut(&mut self, name: Sid) -> Option<&mut Value> {
-        self.vartable
-            .iter_mut()
-            .rev()
-            .find(|it| it.0 == name)
-            .map(|it| &mut it.1)
+    fn get_var_mut(&mut self, idx: usize) -> Option<&mut Value> {
+        self.vartable.get_mut(idx)
     }
 
     pub fn run_str(&mut self, code: &str, print_tokens: bool, print_ast: bool) {
@@ -66,7 +58,8 @@ impl Interpreter {
     }
 
     pub fn run_block(&mut self, prog: &BlockScope) {
-        let vartable_len = self.vartable.len();
+        let framepointer = self.vartable.len();
+
         for stmt in prog {
             match stmt {
                 Statement::Expr(expr) => {
@@ -112,7 +105,7 @@ impl Interpreter {
             }
         }
 
-        self.vartable.truncate(vartable_len);
+        self.vartable.truncate(framepointer);
     }
 
     fn resolve_expr(&mut self, expr: &Expression) -> Value {
@@ -121,13 +114,13 @@ impl Interpreter {
             Expression::String(text) => Value::String(text.clone()),
             Expression::BinOp(bo, lhs, rhs) => self.resolve_binop(bo, lhs, rhs),
             Expression::UnOp(uo, operand) => self.resolve_unop(uo, operand),
-            Expression::Var(name) => self.resolve_var(*name),
+            Expression::Var(name, idx) => self.resolve_var(*name, *idx),
         }
     }
 
-    fn resolve_var(&mut self, name: Sid) -> Value {
-        match self.get_var(name) {
-            Some(val) => val.clone(),
+    fn resolve_var(&mut self, name: Sid, idx: usize) -> Value {
+        match self.get_var(idx) {
+            Some(val) => val,
             None => panic!("Variable '{}' used but not declared", self.stringstore.lookup(name).unwrap()),
         }
     }
@@ -147,14 +140,14 @@ impl Interpreter {
         let rhs = self.resolve_expr(rhs);
 
         match (&bo, &lhs) {
-            (BinOpType::Declare, Expression::Var(name)) => {
-                self.vartable.push((name.clone(), rhs.clone()));
+            (BinOpType::Declare, Expression::Var(_name, _idx)) => {
+                self.vartable.push(rhs.clone());
                 return rhs;
             }
-            (BinOpType::Assign, Expression::Var(name)) => {
-                match self.get_var_mut(*name) {
+            (BinOpType::Assign, Expression::Var(name, idx)) => {
+                match self.get_var_mut(*idx) {
                     Some(val) => *val = rhs.clone(),
-                    None => panic!("Runtime Error: Trying to assign value to undeclared variable"),
+                    None => panic!("Runtime Error: Trying to assign value to undeclared variable: {:?}", self.stringstore.lookup(*name)),
                 }
                 return rhs;
             }

src/parser.rs

@@ -1,7 +1,7 @@
 use std::iter::Peekable;
 
 use crate::ast::*;
-use crate::stringstore::StringStore;
+use crate::stringstore::{Sid, StringStore};
 use crate::token::Token;
 
 /// Parse the given tokens into an abstract syntax tree
@@ -13,6 +13,7 @@ pub fn parse<T: Iterator<Item = Token>, A: IntoIterator<IntoIter = T>>(tokens: A
 struct Parser<T: Iterator<Item = Token>> {
     tokens: Peekable<T>,
     stringstore: StringStore,
+    varstack: Vec<Sid>,
 }
 
 impl<T: Iterator<Item = Token>> Parser<T> {
@@ -20,9 +21,11 @@ impl<T: Iterator<Item = Token>> Parser<T> {
     pub fn new<A: IntoIterator<IntoIter = T>>(tokens: A) -> Self {
         let tokens = tokens.into_iter().peekable();
         let stringstore = StringStore::new();
+        let varstack = Vec::new();
         Self {
             tokens,
             stringstore,
+            varstack,
         }
     }
 
@@ -37,6 +40,7 @@ impl<T: Iterator<Item = Token>> Parser<T> {
     /// Parse tokens into an abstract syntax tree. This will continuously parse statements until
     /// encountering end-of-file or a block end '}' .
     fn parse_scoped_block(&mut self) -> BlockScope {
+        let framepointer = self.varstack.len();
         let mut prog = Vec::new();
 
         loop {
@@ -51,6 +55,8 @@ impl<T: Iterator<Item = Token>> Parser<T> {
             }
         }
 
+        self.varstack.truncate(framepointer);
+
         prog
     }
 
@@ -76,7 +82,20 @@ impl<T: Iterator<Item = Token>> Parser<T> {
 
             // If it is not a loop, try to lex as an expression
             _ => {
-                let stmt = Statement::Expr(self.parse_expr());
+                let mut expr = self.parse_expr();
+
+                match &mut expr {
+                    Expression::BinOp(BinOpType::Declare, lhs, _) => match lhs.as_mut() {
+                        Expression::Var(sid, sp) => {
+                            *sp = self.varstack.len();
+                            self.varstack.push(*sid);
+                        }
+                        _ => panic!("Left hand side of declaration must be variable"),
+                    },
+                    _ => (),
+                }
+
+                let stmt = Statement::Expr(expr);
 
                 // After a statement, there must be a semicolon
                 if !matches!(self.next(), Token::Semicolon) {
@@ -212,7 +231,17 @@ impl<T: Iterator<Item = Token>> Parser<T> {
             // Literal String
             Token::String(text) => Expression::String(self.stringstore.intern_or_lookup(&text)),
 
-            Token::Ident(name) => Expression::Var(self.stringstore.intern_or_lookup(&name)),
+            Token::Ident(name) => {
+                let sid = self.stringstore.intern_or_lookup(&name);
+                let stackpos = self
+                    .varstack
+                    .iter()
+                    .rev()
+                    .position(|it| *it == sid)
+                    .map(|it| self.varstack.len() - it - 1)
+                    .unwrap_or(usize::MAX);
+                Expression::Var(sid, stackpos)
+            }
 
             // Parentheses grouping
             Token::LParen => {