1 files changed, 182 insertions, 0 deletions
diff --git a/src/interpreter.rs b/src/interpreter.rs
new file mode 100644
index 0000000..aa9d441
--- /dev/null
+++ b/src/interpreter.rs
@@ -0,0 +1,182 @@
+use std::collections::HashMap;
+use std::fmt::Display;
+
+use crate::ast::{AstVisitor, Expr, Stmt};
+use crate::lexer::{Literal, TokenType};
+
+#[derive(Default)]
+pub struct AstInterpreter {
+    memory: HashMap<String, (Value, bool)>,
+}
+
+impl AstVisitor<Value> for AstInterpreter {
+    fn visit_stmt(&mut self, stmt: &Stmt) -> Value {
+        match stmt {
+            Stmt::Block(stmts) => {
+                self.interpret(stmts);
+            }
+            Stmt::Expr(expr) => {
+                self.visit_expr(expr);
+            }
+            Stmt::Val { ident, value } => {
+                let value = self.visit_expr(value);
+                self.memory.insert(ident.clone(), (value, false));
+            }
+            Stmt::Var { ident, value } => {
+                let value = self.visit_expr(value);
+                self.memory.insert(ident.clone(), (value, true));
+            }
+            Stmt::Assignment { ident, value } => {
+                if !self.memory.contains_key(ident) {
+                    panic!("Cannot assign to variable that doesn't exist");
+                }
+
+                if !self.memory[ident].1 {
+                    panic!("Cannot mutate value '{ident}'");
+                }
+
+                let value = self.visit_expr(value);
+                self.memory.insert(ident.clone(), (value, true));
+            }
+            Stmt::Function {
+                ident: name,
+                arguments,
+                return_type,
+                body,
+            } => todo!(),
+            Stmt::If { condition, body } => {
+                let result = self.visit_expr(condition);
+                if result == Value::Bool(true) {
+                    self.interpret(body);
+                }
+            }
+            Stmt::For {
+                binding,
+                range,
+                body,
+            } => todo!(),
+            Stmt::Return { value } => todo!(),
+            Stmt::Print { value } => {
+                println!("{}", self.visit_expr(value));
+            }
+        };
+
+        // FIXME: Honestly should probably abandon this "visitor" pattern. 2 functions
+        // with these match statements would work better
+        Value::Nil
+    }
+
+    fn visit_expr(&mut self, expr: &Expr) -> Value {
+        match expr {
+            Expr::Literal(literal) => match literal {
+                Literal::String(value) => Value::String(value.clone()),
+                Literal::Character(value) => Value::String(value.to_string()),
+                Literal::Number(value) => Value::Number(*value),
+                Literal::Bool(value) => Value::Bool(*value),
+                Literal::Nil => Value::Nil,
+            },
+            Expr::Variable(ident) => self.memory.get(ident).unwrap().clone().0,
+            Expr::Grouping(child) => self.visit_expr(child),
+            Expr::Binary { operator, lhs, rhs } => {
+                let lhs = self.visit_expr(lhs);
+                let rhs = self.visit_expr(rhs);
+
+                if let Value::Number(lhs) = lhs && let Value::Number(rhs) = rhs {
+                    match operator {
+                        TokenType::Plus => Value::Number(lhs + rhs),
+                        TokenType::Minus => Value::Number(lhs - rhs),
+                        TokenType::Star => Value::Number(lhs * rhs),
+                        TokenType::Slash => Value::Number(lhs / rhs),
+                        TokenType::Perc => Value::Number(lhs % rhs),
+
+                        TokenType::Gt => Value::Bool(lhs > rhs),
+                        TokenType::GtEq => Value::Bool(lhs >= rhs),
+                        TokenType::Lt => Value::Bool(lhs < rhs),
+                        TokenType::LtEq => Value::Bool(lhs <= rhs),
+
+                        TokenType::BangEq => Value::Bool(lhs != rhs),
+                        TokenType::EqEq => Value::Bool(lhs == rhs),
+
+                        _ => panic!(),
+                    }
+                } else if let Value::Bool(lhs) = lhs && let Value::Bool(rhs) = rhs {
+                    match operator {
+                        TokenType::AmpAmp => Value::Bool(lhs && rhs),
+                        TokenType::PipePipe => Value::Bool(lhs || rhs),
+                        _ => panic!()
+                    }
+                } else if let Value::String(lhs) = lhs && let Value::String(rhs) = rhs {
+                    match operator {
+                        TokenType::Plus => {
+                            let mut value = lhs;
+                            value.push_str(&rhs);
+                            Value::String(value)
+                        },
+                        TokenType::BangEq => Value::Bool(lhs != rhs),
+                        TokenType::EqEq => Value::Bool(lhs == rhs),
+                        _ => panic!()
+                    }
+                } else {
+                    panic!("Invalid operations for types");
+                }
+            }
+            Expr::Unary { operator, expr } => {
+                let value = self.visit_expr(expr);
+
+                match operator {
+                    TokenType::Bang => {
+                        let Value::Bool(value) = value else {
+                            panic!("Invalid operations for types");
+                        };
+
+                        Value::Bool(!value)
+                    }
+                    TokenType::Plus => value,
+                    TokenType::Minus => {
+                        let Value::Number(value) = value else {
+                            panic!("Invalid operations for types");
+                        };
+
+                        Value::Number(-value)
+                    }
+                    _ => panic!(),
+                }
+            }
+            _ => unimplemented!("{:?}", expr),
+        }
+    }
+}
+
+impl AstInterpreter {
+    pub fn interpret(&mut self, stmts: &Vec<Stmt>) {
+        for stmt in stmts {
+            self.visit_stmt(stmt);
+        }
+    }
+}
+
+#[derive(Debug, Clone, Eq, PartialEq)]
+pub enum Value {
+    Number(i32),
+    String(String),
+    Bool(bool),
+    Nil,
+}
+
+impl Display for Value {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            Value::Number(value) => write!(f, "{value}")?,
+            Value::String(value) => write!(f, "{value}")?,
+            Value::Bool(value) => write!(f, "{value}")?,
+            Value::Nil => write!(f, "nil")?,
+        }
+
+        Ok(())
+    }
+}
+
+#[cfg(test)]
+mod test {
+    //
+}