diff --git a/src/cli.rs b/src/cli.rs
new file mode 100644
index 0000000..8761b84
--- /dev/null
+++ b/src/cli.rs
@@ -0,0 +1,45 @@
+use std::path::PathBuf;
+
+use pico_args::Arguments;
+
+#[derive(Debug)]
+pub enum Error {
+    ArgsError(pico_args::Error),
+    InvalidCommand(String),
+    PrintUsage,
+}
+
+impl From<pico_args::Error> for Error {
+    fn from(value: pico_args::Error) -> Self {
+        Error::ArgsError(value)
+    }
+}
+
+pub enum Command {
+    Parse { source: PathBuf },
+    Run { source: PathBuf },
+    Repl,
+}
+
+impl Command {
+    pub fn from_environment() -> Result<Self, Error> {
+        let mut args = Arguments::from_env();
+        if args.contains(["-h", "--help"]) {
+            return Err(Error::PrintUsage);
+        }
+        let cmd = match args.subcommand()?.as_deref() {
+            Some("parse") => {
+                let source = args.free_from_str()?;
+                Command::Parse { source }
+            }
+            Some("run") => {
+                let source = args.free_from_str()?;
+                Command::Run { source }
+            }
+            Some("repl") => Command::Repl,
+            Some(cmd) => return Err(Error::InvalidCommand(cmd.to_string())),
+            None => return Err(Error::PrintUsage),
+        };
+        Ok(cmd)
+    }
+}
diff --git a/src/interpreter.rs b/src/interpreter.rs
deleted file mode 100644
index 9691e62..0000000
--- a/src/interpreter.rs
+++ /dev/null
@@ -1,150 +0,0 @@
-use std::collections::HashMap;
-
-use crate::syntax::{Expression, Name, Program, Statement};
-
-pub type Environment = HashMap<Name, Value>;
-
-#[derive(Debug, Clone)]
-pub enum Value {
-    Boolean(bool),
-    Integer(i64),
-    Closure(Vec<Name>, Expression, Environment),
-}
-
-pub struct Interpreter {
-    environment: Environment,
-}
-
-#[derive(Debug)]
-pub enum InterpreterError {
-    VariableNotFound(Name),
-    IncorrectArgumentCount(usize, usize),
-    NonFunctionCall(Value),
-    EmptyProgram,
-    ExecutionError(String),
-}
-
-impl From<String> for InterpreterError {
-    fn from(s: String) -> Self {
-        InterpreterError::ExecutionError(s)
-    }
-}
-
-impl std::fmt::Display for InterpreterError {
-    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
-        match self {
-            InterpreterError::VariableNotFound(name) => write!(f, "Variable '{}' not found", name),
-            InterpreterError::IncorrectArgumentCount(expected, actual) => {
-                write!(f, "Expected {} arguments, but got {}", expected, actual)
-            }
-            InterpreterError::NonFunctionCall(value) => {
-                write!(f, "Function call on non-function value: {:?}", value)
-            }
-            InterpreterError::EmptyProgram => write!(f, "Program is empty"),
-            InterpreterError::ExecutionError(s) => write!(f, "Execution error: {}", s),
-        }
-    }
-}
-
-type Result<T> = std::result::Result<T, InterpreterError>;
-
-impl Interpreter {
-    pub fn new() -> Self {
-        Self {
-            environment: Environment::new(),
-        }
-    }
-
-    pub fn interpret_statement(&mut self, statement: &Statement) -> Result<Value> {
-        match statement {
-            Statement::Binding(name, expression) => {
-                let value = self.evaluate(expression)?;
-                self.environment.insert(name.clone(), value.clone());
-                Ok(value)
-            }
-            Statement::Expression(expression) => self.evaluate(expression),
-        }
-    }
-
-    pub fn interpret(&mut self, program: &Program) -> Result<Value> {
-        let mut result = None;
-
-        for statement in program {
-            result = Some(self.interpret_statement(statement)?);
-        }
-
-        match result {
-            Some(value) => Ok(value),
-            None => Err(InterpreterError::EmptyProgram),
-        }
-    }
-
-    fn evaluate(&mut self, expression: &Expression) -> Result<Value> {
-        match expression {
-            Expression::Variable(name) => self
-                .environment
-                .get(name)
-                .cloned()
-                .ok_or_else(|| InterpreterError::VariableNotFound(name.clone())),
-
-            Expression::Boolean(value) => Ok(Value::Boolean(*value)),
-
-            Expression::Integer(value) => Ok(Value::Integer(*value)),
-
-            Expression::Lambda(params, body) => Ok(Value::Closure(
-                params.clone(),
-                *body.clone(),
-                self.environment.clone(),
-            )),
-
-            Expression::Call(function, args) => {
-                let function_value = self.evaluate(function)?;
-
-                match function_value {
-                    Value::Closure(params, body, mut environment) => {
-                        if params.len() != args.len() {
-                            return Err(InterpreterError::IncorrectArgumentCount(
-                                params.len(),
-                                args.len(),
-                            ));
-                        }
-
-                        let mut arg_values = Vec::new();
-                        for arg in args {
-                            arg_values.push(self.evaluate(arg)?);
-                        }
-
-                        // Bind argument values to parameter names in a new environment
-                        for (param, arg_value) in params.iter().zip(arg_values.into_iter()) {
-                            environment.insert(param.clone(), arg_value);
-                        }
-
-                        // Evaluate the body expression in the new environment
-                        let mut interpreter = Interpreter { environment };
-                        interpreter.evaluate(&body)
-                    }
-                    _ => Err(InterpreterError::NonFunctionCall(function_value)),
-                }
-            }
-
-            Expression::Block(statements, expression) => {
-                let new_environment = self.environment.clone();
-
-                for statement in statements {
-                    self.interpret_statement(statement)?;
-                }
-
-                let mut interpreter = Interpreter {
-                    environment: new_environment,
-                };
-                interpreter.evaluate(expression)
-            }
-        }
-    }
-}
-
-impl Default for Interpreter {
-    fn default() -> Self {
-        Self::new()
-    }
-}
diff --git a/src/lib.rs b/src/lib.rs
index bf5927c..b90dd89 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1,5 +1,3 @@
-use lalrpop_util::lalrpop_mod;
-
-pub mod interpreter;
-lalrpop_mod!(pub parser);
+pub mod cli;
+pub mod phase;
 pub mod syntax;
diff --git a/src/main.rs b/src/main.rs
index 4b6dd04..608ffa3 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -1,17 +1,46 @@
-use std::env::args;
 use std::fs::read_to_string;
 use std::io::{stdin, stdout, BufRead, Write};
 use std::path::Path;
 use std::process::exit;
 
-use mul::interpreter::Interpreter;
-use mul::parser::{ProgramParser, StatementParser};
+use mul::cli::{Command, Error};
+use mul::phase::parse::{parse_program, parse_repl_line};
+
+fn main() -> Result<(), Error> {
+    let command = Command::from_environment()?;
+    match command {
+        Command::Parse { source } => parse(source.as_path()),
+        Command::Run { source } => run(source.as_path()),
+        Command::Repl => repl(),
+    }
+    Ok(())
+}
+
+fn parse(file: &Path) {
+    let content = read_to_string(file).expect("Failed to read file");
+    let program = parse_program(content.as_str()).unwrap_or_else(|e| {
+        eprintln!("{e}");
+        exit(1);
+    });
+    println!("{program:#?}");
+}
+
+fn run(file: &Path) {
+    let content = read_to_string(file).expect("Failed to read file");
+    let program = parse_program(content.as_str()).unwrap_or_else(|e| {
+        eprintln!("{e}");
+        exit(1);
+    });
+    // let v = interpreter.interpret(&program).unwrap_or_else(|e| {
+    //     eprintln!("{e}");
+    //     exit(1);
+    // });
+    // println!("{v:?}")
+}
 
 fn repl() {
     let mut stdin = stdin().lock();
     let mut stdout = stdout().lock();
-    let parser = StatementParser::new();
-    let mut intepreter = Interpreter::new();
     loop {
         let mut line = String::new();
         print!("> ");
@@ -26,7 +55,7 @@ fn repl() {
         if !line.trim_end().ends_with(';') {
             line.push(';');
         }
-        let parsed = match parser.parse(&line) {
+        let parsed = match parse_repl_line(&line) {
             Ok(parsed) => parsed,
             Err(lalrpop_util::ParseError::UnrecognizedEOF { .. }) => break,
             Err(e) => {
@@ -34,35 +63,13 @@ fn repl() {
                 continue;
             }
         };
-        match intepreter.interpret_statement(&parsed) {
-            Ok(value) => println!("{value:?}"),
-            Err(e) => {
-                eprintln!("{e}");
-                continue;
-            }
-        };
-    }
-}
-
-fn build(file: &Path) {
-    let content = read_to_string(file).expect("Failed to read file");
-    let parser = ProgramParser::new();
-    let mut interpreter = Interpreter::new();
-    let program = parser.parse(content.as_str()).unwrap_or_else(|e| {
-        eprintln!("{e}");
-        exit(1);
-    });
-    let v = interpreter.interpret(&program).unwrap_or_else(|e| {
-        eprintln!("{e}");
-        exit(1);
-    });
-    println!("{v:?}")
-}
-
-fn main() {
-    if let Some(file) = args().nth(1) {
-        build(file.as_ref())
-    } else {
-        repl()
+        println!("{parsed:?}");
+        // match intepreter.interpret_statement(&parsed) {
+        //     Ok(value) => println!("{value:?}"),
+        //     Err(e) => {
+        //         eprintln!("{e}");
+        //         continue;
+        //     }
+        // };
     }
 }
diff --git a/src/parser.lalrpop b/src/parser.lalrpop
deleted file mode 100644
index 5fdfd15..0000000
--- a/src/parser.lalrpop
+++ /dev/null
@@ -1,52 +0,0 @@
-use crate::syntax::{Expression, Name, Program, Statement};
-
-grammar;
-
-pub Program: Program = Statement*;
-
-pub Statement: Statement = {
-    "let" <Name> "=" <Expression> ";" => Statement::Binding(<>),
-    <Block> ";"? => Statement::Expression(<>),
-    <Simple> ";" => Statement::Expression(<>),
-};
-
-pub Expression = {
-    Simple,
-    Block,
-};
-
-Simple: Expression = {
-    "|" <parameters:Comma<Name>> "|" <body:Expression> => Expression::Lambda(parameters, Box::new(body)),
-    Atom,
-};
-
-Atom: Expression = {
-    Name => Expression::Variable(<>),
-    <callee:Atom> "(" <arguments:Comma<Expression>> ")" => Expression::Call(Box::new(callee), arguments),
-    Integer => Expression::Integer(<>),
-    Boolean => Expression::Boolean(<>),
-    "(" <Expression> ")",
-};
-
-Block: Expression =
-    "{" <statements:Statement*> <result:Expression> "}" => Expression::Block(statements, Box::new(result));
-
-// TODO: decide on identifier syntax
-Name: Name = r"[a-zA-Z_]+" => <>.to_string();
-
-Integer: i64 = r"[0-9]+" => <>.parse::<i64>().unwrap();
-
-Boolean: bool = {
-    "true" => true,
-    "false" => false,
-}
-
-Comma<T>: Vec<T> = {
-    <mut v:(<T> ",")*> <e:T?> => match e {
-        None => v,
-        Some(e) => {
-            v.push(e);
-            v
-        }
-    }
-};
diff --git a/src/phase.rs b/src/phase.rs
new file mode 100644
index 0000000..ea86848
--- /dev/null
+++ b/src/phase.rs
@@ -0,0 +1 @@
+pub mod parse;
diff --git a/src/phase/parse.rs b/src/phase/parse.rs
new file mode 100644
index 0000000..d288f7a
--- /dev/null
+++ b/src/phase/parse.rs
@@ -0,0 +1,15 @@
+use lalrpop_util::{lalrpop_mod, lexer::Token, ParseError};
+
+use crate::syntax::{self, Line};
+
+lalrpop_mod!(parser, "/phase/parse/parser.rs");
+
+pub type Result<'input, T> = std::result::Result<T, ParseError<usize, Token<'input>, &'static str>>;
+
+pub fn parse_program(input: &str) -> Result<syntax::Program> {
+    parser::ProgramParser::new().parse(input)
+}
+
+pub fn parse_repl_line(input: &str) -> Result<Line> {
+    parser::LineParser::new().parse(input)
+}
diff --git a/src/phase/parse/parser.lalrpop b/src/phase/parse/parser.lalrpop
new file mode 100644
index 0000000..e1bfe11
--- /dev/null
+++ b/src/phase/parse/parser.lalrpop
@@ -0,0 +1,69 @@
+use crate::syntax::{
+    Binding,
+    Block,
+    Expression,
+    Item,
+    Line,
+    Name,
+    Program,
+};
+
+grammar;
+
+pub Program: Program = Item*;
+
+pub Line: Line = {
+    Item => Line::Item(<>),
+    Binding => Line::Binding(<>),
+    <Expression> ";"? => Line::Expression(<>),
+}
+
+Item: Item = {
+    "fn" <name:Name> "(" <parameters:Comma<Name>> ")" <body:Block> ";"? => Item::Fn { <> },
+}
+
+Binding: Binding =
+    "let" <Name> "=" <Expression> ";" => Binding(<>);
+
+Expression: Expression = {
+    Simple,
+    Boxed<Block> => Expression::Block(<>),
+};
+
+Simple: Expression = {
+    "|" <parameters:Comma<Name>> "|" <result:Boxed<Expression>> => Expression::Lambda { <> },
+    Atom,
+};
+
+Atom: Expression = {
+    Name => Expression::Variable(<>),
+    <callee:Boxed<Atom>> "(" <arguments:Comma<Expression>> ")" => Expression::Call { <> },
+    Integer => Expression::Integer(<>),
+    Boolean => Expression::Boolean(<>),
+    "(" <Expression> ")",
+};
+
+Block: Block =
+    "{" <bindings:Binding*> <result:Expression> "}" => Block { <> };
+
+// TODO: decide on identifier syntax
+Name: Name = r"[a-zA-Z_]+" => <>.to_string();
+
+Integer: i64 = r"[0-9]+" => <>.parse::<i64>().unwrap();
+
+Boolean: bool = {
+    "true" => true,
+    "false" => false,
+}
+
+Boxed<T>: Box<T> = T => Box::new(<>);
+
+Comma<T>: Vec<T> = {
+    <mut v:(<T> ",")*> <e:T?> => match e {
+        None => v,
+        Some(e) => {
+            v.push(e);
+            v
+        }
+    }
+};
diff --git a/src/syntax.rs b/src/syntax.rs
index 9f91f8b..28068ea 100644
--- a/src/syntax.rs
+++ b/src/syntax.rs
@@ -1,19 +1,44 @@
 pub type Name = String;
 
-pub type Program = Vec<Statement>;
+pub type Program = Vec<Item>;
 
 #[derive(Debug, Clone)]
-pub enum Statement {
-    Binding(Name, Expression),
+pub enum Line {
+    Item(Item),
+    Binding(Binding),
     Expression(Expression),
 }
 
+#[derive(Debug, Clone)]
+pub enum Item {
+    Fn {
+        name: Name,
+        parameters: Vec<Name>,
+        body: Block,
+    },
+}
+
+#[derive(Debug, Clone)]
+pub struct Binding(pub Name, pub Expression);
+
 #[derive(Debug, Clone)]
 pub enum Expression {
     Variable(Name),
-    Block(Vec<Statement>, Box<Expression>),
-    Lambda(Vec<Name>, Box<Expression>),
-    Call(Box<Expression>, Vec<Expression>),
+    Block(Box<Block>),
+    Lambda {
+        parameters: Vec<Name>,
+        result: Box<Expression>,
+    },
+    Call {
+        callee: Box<Expression>,
+        arguments: Vec<Expression>,
+    },
     Boolean(bool),
     Integer(i64),
 }
+
+#[derive(Debug, Clone)]
+pub struct Block {
+    pub bindings: Vec<Binding>,
+    pub result: Expression,
+}