added evaluating, basically just added support for adding and

subtracting

.vscode/settings.json

@@ -1,3 +1,3 @@
 {
-  "cSpell.words": ["Peekable"]
+  "cSpell.words": ["binop", "Peekable"]
 }

src/frontend.rs

@@ -1,28 +0,0 @@
-use std::process;
-
-use crate::parser::Parser;
-
-pub fn repl() {
-    // Read-Eval-Print Loop
-    use std::io::{self, Write};
-
-    println!("Welcome to the Riv Lang REPL! Type 'exit' to quit.");
-
-    loop {
-        print!("> ");
-        io::stdout().flush().unwrap();
-
-        let mut input = String::new();
-        io::stdin().read_line(&mut input).unwrap();
-
-        let input = input.trim().to_string();
-
-        if input == "exit" {
-            process::exit(0);
-        }
-
-        let program = Parser::new(input).produce_ast();
-
-        println!("{:#?}", program);
-    }
-}

src/frontend/mod.rs

@@ -0,0 +1,3 @@
+pub mod ast;
+pub mod lexer;
+pub mod parser;

src/main.rs

@@ -1,9 +1,39 @@
 use clap::Parser;
+use std::process;
 
-mod ast;
 mod frontend;
-mod lexer;
+use frontend::ast;
-mod parser;
+use frontend::lexer;
+use frontend::parser;
+
+mod runtime;
+use runtime::interpreter::evaluate;
+
+pub fn repl() {
+    // Read-Eval-Print Loop
+    use std::io::{self, Write};
+
+    println!("Welcome to the Riv Lang REPL! Type 'exit' to quit.");
+
+    loop {
+        print!("> ");
+        io::stdout().flush().unwrap();
+
+        let mut input = String::new();
+        io::stdin().read_line(&mut input).unwrap();
+
+        let input = input.trim().to_string();
+
+        if input == "exit" {
+            process::exit(0);
+        }
+
+        let program = parser::Parser::new(input).produce_ast();
+
+        let result = evaluate(frontend::ast::NodeType::Program(program));
+        println!("{:#?}", result);
+    }
+}
 
 #[derive(clap::Parser)]
 struct CLI {
@@ -20,7 +50,7 @@ fn main() -> Result<(), Box<dyn std::error::Error>> {
     let cli = CLI::parse();
 
     if cli.repl {
-        frontend::repl();
+        repl();
     } else if let Some(file_path) = cli.file {
         let source_code = std::fs::read_to_string(file_path)?;
         let mut parser = parser::Parser::new(source_code);

src/runtime/interpreter.rs

@@ -0,0 +1,61 @@
+use std::process;
+
+use crate::frontend::ast::{BinaryExpr, NodeType, Program};
+use crate::runtime::values::ValueType;
+
+fn eval_program(program: Program) -> ValueType {
+    // Initialize with your equivalent of NullVal
+    let mut last_evaluated = ValueType::Null;
+
+    // Iterate through each statement in the program body
+    for statement in program.body {
+        last_evaluated = evaluate(statement);
+    }
+
+    last_evaluated
+}
+
+fn eval_binop(binop: BinaryExpr) -> ValueType {
+    let lhs = evaluate(*binop.left);
+    let rhs = evaluate(*binop.right);
+
+    match (&lhs, &rhs) {
+        (ValueType::Number(l), ValueType::Number(r)) => eval_num_binop(*l, *r, binop.operator),
+        _ => ValueType::Null,
+    }
+}
+
+fn eval_num_binop(lhs: f64, rhs: f64, operator: String) -> ValueType {
+    let result: f64;
+
+    match operator.as_str() {
+        "+" => result = lhs + rhs,
+        "-" => result = lhs - rhs,
+        "*" => result = lhs * rhs,
+        // TODO: Handle division by zero
+        "/" => result = lhs / rhs,
+        "%" => result = lhs % rhs,
+        _ => {
+            eprintln!("Unknown operator: {}", operator);
+            process::exit(1);
+        }
+    }
+
+    ValueType::Number(result)
+}
+
+pub fn evaluate(node: NodeType) -> ValueType {
+    match node {
+        NodeType::NumericLiteral(n) => ValueType::Number(n.value),
+        NodeType::NullLiteral(_) => ValueType::Null,
+        NodeType::BinaryExpr(e) => eval_binop(e),
+        NodeType::Program(p) => eval_program(p),
+        _ => {
+            eprintln!(
+                "Evaluation for node type {:#?} is not implemented yet.",
+                node
+            );
+            process::exit(1);
+        }
+    }
+}

src/runtime/mod.rs

@@ -0,0 +1,2 @@
+pub mod interpreter;
+pub mod values;

src/runtime/values.rs

@@ -0,0 +1,5 @@
+#[derive(Debug, Clone, PartialEq)]
+pub enum ValueType {
+    Null,
+    Number(f64),
+}