diff --git a/src/asts.rs b/src/asts.rs
new file mode 100644
index 0000000..b743795
--- /dev/null
+++ b/src/asts.rs
@@ -0,0 +1 @@
+pub mod hil;
diff --git a/src/asts/hil.rs b/src/asts/hil.rs
new file mode 100644
index 0000000..f25246e
--- /dev/null
+++ b/src/asts/hil.rs
@@ -0,0 +1,173 @@
+use crate::variable_map::{Variable, VariableMap};
+use pretty::{DocAllocator, DocBuilder, Pretty};
+
+#[derive(Debug, PartialEq)]
+pub struct Program<Annotation> {
+    pub statements: Vec<Statement<Annotation>>,
+}
+
+impl<Annotation> Program<Annotation> {
+    pub fn pretty<'a, D, A>(
+        &self,
+        variable_map: &VariableMap,
+        allocator: &'a D,
+    ) -> DocBuilder<'a, D, A>
+    where
+        A: 'a,
+        D: ?Sized + DocAllocator<'a, A>,
+    {
+        let mut result = allocator.nil();
+
+        for stmt in self.statements.iter() {
+            result = result
+                .append(stmt.pretty(variable_map, allocator))
+                .append(allocator.text(";"))
+                .append(allocator.hardline());
+        }
+
+        result
+    }
+}
+
+#[derive(Debug, PartialEq)]
+pub enum Statement<Annotation> {
+    Binding(Annotation, Variable, Expression<Annotation>),
+    Print(Annotation, Variable),
+}
+
+impl<Annotation> Statement<Annotation> {
+    pub fn pretty<'a, D, A>(
+        &self,
+        variable_map: &VariableMap,
+        allocator: &'a D,
+    ) -> DocBuilder<'a, D, A>
+    where
+        A: 'a,
+        D: ?Sized + DocAllocator<'a, A>,
+    {
+        match self {
+            Statement::Binding(_, var, expr) => {
+                let name = variable_map.get_name(*var).unwrap_or("<unknown>");
+
+                allocator
+                    .text(name.to_string())
+                    .append(allocator.space())
+                    .append(allocator.text("="))
+                    .append(allocator.space())
+                    .append(expr.pretty(variable_map, allocator))
+            }
+            Statement::Print(_, var) => {
+                let name = variable_map.get_name(*var).unwrap_or("<unknown>");
+
+                allocator
+                    .text("print")
+                    .append(allocator.space())
+                    .append(allocator.text(name.to_string()))
+            }
+        }
+    }
+}
+
+#[derive(Debug, PartialEq)]
+pub enum Expression<Annotation> {
+    Value(Annotation, Value),
+    Reference(Annotation, Variable),
+    Primitive(Annotation, Primitive, Vec<Expression<Annotation>>),
+}
+
+#[derive(Clone, Copy, Debug, PartialEq)]
+pub enum Primitive {
+    Plus,
+    Minus,
+    Times,
+    Divide,
+}
+
+impl<Annotation> Expression<Annotation> {
+    fn pretty<'a, A, D>(&self, variable_map: &VariableMap, allocator: &'a D) -> DocBuilder<'a, D, A>
+    where
+        A: 'a,
+        D: ?Sized + DocAllocator<'a, A>,
+    {
+        match self {
+            Expression::Value(_, val) => val.pretty(allocator),
+            Expression::Reference(_, var) => {
+                let name = variable_map.get_name(*var).unwrap_or("<unknown>");
+
+                allocator.text(name.to_string())
+            }
+            Expression::Primitive(_, op, exprs) if exprs.len() == 1 => op
+                .pretty(allocator)
+                .append(exprs[0].pretty(variable_map, allocator)),
+            Expression::Primitive(_, op, exprs) if exprs.len() == 2 => {
+                let left = exprs[0].pretty(variable_map, allocator);
+                let right = exprs[1].pretty(variable_map, allocator);
+
+                left.append(allocator.space())
+                    .append(op.pretty(allocator))
+                    .append(allocator.space())
+                    .append(right)
+                    .parens()
+            }
+            Expression::Primitive(_, op, exprs) => {
+                allocator.text(format!("!!{:?} with {} arguments!!", op, exprs.len()))
+            }
+        }
+    }
+}
+
+impl<'a, 'b, D, A> Pretty<'a, D, A> for &'b Primitive
+where
+    A: 'a,
+    D: ?Sized + DocAllocator<'a, A>,
+{
+    fn pretty(self, allocator: &'a D) -> DocBuilder<'a, D, A> {
+        match self {
+            Primitive::Plus => allocator.text("+"),
+            Primitive::Minus => allocator.text("-"),
+            Primitive::Times => allocator.text("*"),
+            Primitive::Divide => allocator.text("/"),
+        }
+    }
+}
+
+#[derive(Debug, PartialEq)]
+pub enum Value {
+    Number(Option<u8>, i128),
+}
+
+impl<'a, 'b, D, A> Pretty<'a, D, A> for &'b Value
+where
+    A: 'a,
+    D: ?Sized + DocAllocator<'a, A>,
+{
+    fn pretty(self, allocator: &'a D) -> DocBuilder<'a, D, A> {
+        match self {
+            Value::Number(opt_base, value) => {
+                let value_str = match opt_base {
+                    None => format!("{}", value),
+                    Some(2) => format!("0b{:b}", value),
+                    Some(8) => format!("0o{:o}", value),
+                    Some(10) => format!("0d{}", value),
+                    Some(16) => format!("0x{:x}", value),
+                    Some(_) => format!("!!{:x}!!", value),
+                };
+
+                allocator.text(value_str)
+            }
+        }
+    }
+}
+
+#[derive(Clone, Copy)]
+struct CommaSep {}
+
+impl<'a, 'b, D, A> Pretty<'a, D, A> for CommaSep
+where
+    A: 'a,
+    D: ?Sized + DocAllocator<'a, A>,
+{
+    fn pretty(self, allocator: &'a D) -> DocBuilder<'a, D, A> {
+        allocator.text(",").append(allocator.space())
+    }
+}
diff --git a/src/bin.rs b/src/bin.rs
index a7d0aa4..99d6d6f 100644
--- a/src/bin.rs
+++ b/src/bin.rs
@@ -3,10 +3,8 @@ use codespan_reporting::diagnostic::Diagnostic;
 use codespan_reporting::files::SimpleFiles;
 use codespan_reporting::term;
 use codespan_reporting::term::termcolor::{ColorChoice, StandardStream};
-use ngr::error::Error;
-use ngr::syntax::Program;
-use pretty::{Arena, Pretty};
-use std::fs;
+use ngr::passes::run_front_end;
+use pretty::Arena;
 
 #[derive(Parser, Debug)]
 #[clap(author, version, about, long_about = None)]
@@ -19,36 +17,27 @@ struct CommandLineArguments {
     file: String,
 }
 
-fn compile_file(
-    file_database: &mut SimpleFiles<String, String>,
-    initial_file_name: &str,
-) -> Result<Program, Error> {
-    let initial_file_contents = fs::read_to_string(initial_file_name)?;
-    let initial_file = file_database.add(initial_file_name.to_string(), initial_file_contents);
-    let db_version = file_database.get(initial_file)?;
-    let db_version_source = db_version.source();
-    Ok(Program::parse(initial_file, db_version_source)?)
-}
-
 fn main() {
     let args = CommandLineArguments::parse();
     let mut file_database = SimpleFiles::new();
     let initial_file_name = &args.file;
+    let mut hil_conversion_result = run_front_end(&mut file_database, initial_file_name);
 
-    match compile_file(&mut file_database, initial_file_name) {
-        Ok(p) => {
-            let arena = Arena::new();
-            p.pretty(&arena)
-                .into_doc()
-                .render_colored(72, StandardStream::stdout(ColorChoice::Auto))
-                .unwrap()
-        }
-        Err(e) => {
-            let diagnostic = Diagnostic::from(e);
-            let writer = StandardStream::stderr(ColorChoice::Auto);
-            let config = codespan_reporting::term::Config::default();
+    let writer = StandardStream::stderr(ColorChoice::Auto);
+    let config = codespan_reporting::term::Config::default();
 
-            term::emit(&mut writer.lock(), &config, &file_database, &diagnostic).unwrap();
-        }
+    for error in hil_conversion_result.errors.drain(..) {
+        term::emit(&mut writer.lock(), &config, &file_database, &Diagnostic::from(error)).unwrap();
+    }
+    for warning in hil_conversion_result.warnings.drain(..) {
+        term::emit(&mut writer.lock(), &config, &file_database, &Diagnostic::from(warning)).unwrap();
+    }
+
+    if let Some((tree, variable_map)) = hil_conversion_result.result {
+        let arena = Arena::new();
+        tree.pretty(&variable_map, &arena)
+            .into_doc()
+            .render_colored(72, StandardStream::stdout(ColorChoice::Auto))
+            .unwrap()
     }
 }
diff --git a/src/error.rs b/src/errors.rs
similarity index 79%
rename from src/error.rs
rename to src/errors.rs
index eee0d05..09b2d75 100644
--- a/src/error.rs
+++ b/src/errors.rs
@@ -15,6 +15,12 @@ pub enum Error {
 
     #[error("Error in parser: {0}")]
     ParserError(#[from] ParseError<Location, Token, LexerError>),
+
+    #[error("Internal error: Couldn't deal with bound variable with no bindiing site ({0})")]
+    BindingSiteFailure(Location, String),
+
+    #[error("Unbound variable '{0}'")]
+    UnboundVariable(Location, String),
 }
 
 fn locations_to_labels(start: &Location, end: &Location) -> Vec<Label<usize>> {
@@ -136,6 +142,34 @@ impl From<Error> for Diagnostic<usize> {
                     },
                 },
             },
+
+            Error::BindingSiteFailure(location, name) => match location {
+                Location::Manufactured => Diagnostic::error().with_message(format!(
+                    "Internal Error: Lost binding site for bound variable {}",
+                    name
+                )),
+                Location::InFile(file_id, offset) => Diagnostic::error()
+                    .with_labels(vec![
+                        Label::primary(*file_id, *offset..*offset).with_message("discovered here")
+                    ])
+                    .with_message(format!(
+                        "Internal Error: Lost binding site for bound variable {}",
+                        name
+                    )),
+            },
+
+            Error::UnboundVariable(location, name) => match location {
+                Location::Manufactured => Diagnostic::error().with_message(format!(
+                    "Unbound variable '{}'",
+                    name
+                )),
+                Location::InFile(file_id, offset) => Diagnostic::error()
+                    .with_labels(vec![
+                        Label::primary(*file_id, *offset..*offset).with_message("unbound here")
+                    ])
+                    .with_message(format!("Unbound variable '{}'", name)),
+
+            }
         }
     }
 }
diff --git a/src/lib.rs b/src/lib.rs
index 4c51213..1936d8f 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1,3 +1,7 @@
-pub mod error;
+pub mod asts;
+pub mod errors;
+pub mod passes;
 pub mod syntax;
 pub mod util;
+pub mod variable_map;
+pub mod warnings;
diff --git a/src/passes.rs b/src/passes.rs
new file mode 100644
index 0000000..fad4677
--- /dev/null
+++ b/src/passes.rs
@@ -0,0 +1,64 @@
+use codespan_reporting::files::SimpleFiles;
+use crate::asts::hil;
+use crate::errors::Error;
+use crate::syntax;
+use crate::syntax::Location;
+use crate::variable_map::VariableMap;
+use crate::warnings::Warning;
+use std::fs;
+
+mod syntax_to_hil;
+
+pub struct PassResult<T> {
+    pub result: T,
+    pub warnings: Vec<Warning>,
+    pub errors: Vec<Error>,
+}
+
+impl<T,E> From<E> for PassResult<Option<T>>
+ where
+  Error: From<E>
+{
+    fn from(x: E) -> Self {
+        PassResult {
+            result: None,
+            warnings: vec![],
+            errors: vec![Error::from(x)],
+        }
+    }
+}
+
+pub fn run_front_end(
+    file_database: &mut SimpleFiles<String, String>,
+    initial_file_name: &str,
+) -> PassResult<Option<(hil::Program<Location>, VariableMap)>> {
+    let initial_file_contents = match fs::read_to_string(initial_file_name) {
+        Ok(x) => x,
+        Err(e) => return PassResult::from(e),
+    };
+
+    let initial_file = file_database.add(initial_file_name.to_string(), initial_file_contents);
+    let db_version = match file_database.get(initial_file) {
+        Ok(x) => x,
+        Err(e) => return PassResult::from(e),
+    };
+    let db_version_source = db_version.source();
+    let raw_syntax = match syntax::Program::parse(initial_file, db_version_source) {
+        Ok(x) => x,
+        Err(e) => return PassResult::from(e),
+    };
+
+    let mut variable_map = VariableMap::empty();
+    let conversion_result = hil::Program::convert(raw_syntax, &mut variable_map);
+    let result = if conversion_result.errors.is_empty() {
+        Some((conversion_result.result, variable_map))
+    } else {
+        None
+    };
+
+    PassResult {
+        result,
+        warnings: conversion_result.warnings,
+        errors: conversion_result.errors,
+    }
+}
\ No newline at end of file
diff --git a/src/passes/syntax_to_hil.rs b/src/passes/syntax_to_hil.rs
new file mode 100644
index 0000000..21b6b55
--- /dev/null
+++ b/src/passes/syntax_to_hil.rs
@@ -0,0 +1,152 @@
+use crate::asts::hil::{self, Primitive};
+use crate::errors::Error;
+use crate::passes::PassResult;
+use crate::syntax;
+use crate::syntax::Location;
+use crate::variable_map::VariableMap;
+use crate::warnings::Warning;
+
+impl hil::Program<Location> {
+    pub fn convert(
+        mut input: syntax::Program,
+        var_map: &mut VariableMap,
+    ) -> PassResult<hil::Program<Location>> {
+        let mut statements = Vec::new();
+        let mut warnings = Vec::new();
+        let mut errors = Vec::new();
+
+        for syntax_stmt in input.statements.drain(..) {
+            let mut result = hil::Statement::convert(syntax_stmt, var_map);
+
+            statements.push(result.result);
+            warnings.append(&mut result.warnings);
+            errors.append(&mut result.errors);
+        }
+
+        PassResult {
+            result: hil::Program { statements },
+            warnings,
+            errors,
+        }
+    }
+}
+
+impl hil::Statement<Location> {
+    fn convert(
+        input: syntax::Statement,
+        var_map: &mut VariableMap,
+    ) -> PassResult<hil::Statement<Location>> {
+        match input {
+            syntax::Statement::Binding(loc, variable_name, expr) => {
+                let mut expr_result = hil::Expression::convert(expr, var_map);
+                let mut errors = Vec::new();
+                let mut warnings = Vec::new();
+
+                if let Some(var) = var_map.get_variable(&variable_name) {
+                    if let Some(orig_loc) = var_map.get_binding_site(var) {
+                        warnings.push(Warning::ShadowedVariable(orig_loc, loc.clone(), variable_name.clone()));
+                    } else {
+                        errors.push(Error::BindingSiteFailure(
+                            loc.clone(),
+                            variable_name.clone(),
+                        ));
+                    }
+                }
+
+                let variable = var_map.add(variable_name, loc.clone());
+                let result = hil::Statement::Binding(loc, variable, expr_result.result);
+                warnings.append(&mut expr_result.warnings);
+                errors.append(&mut expr_result.errors);
+
+                PassResult {
+                    result,
+                    warnings,
+                    errors,
+                }
+            }
+
+            syntax::Statement::Print(variable_loc, variable_name) => match var_map.get_variable(&variable_name) {
+                None => PassResult {
+                    result: hil::Statement::Print(Location::Manufactured, 0),
+                    warnings: vec![],
+                    errors: vec![Error::UnboundVariable(variable_loc, variable_name)],
+                },
+
+                Some(variable) => PassResult {
+                    result: hil::Statement::Print(variable_loc, variable),
+                    warnings: vec![],
+                    errors: vec![],
+                },
+            }
+        }
+    }
+}
+
+impl hil::Expression<Location> {
+    fn convert(
+        input: syntax::Expression,
+        var_map: &mut VariableMap,
+    ) -> PassResult<hil::Expression<Location>> {
+        match input {
+            syntax::Expression::Value(location, value) => PassResult {
+                result: hil::Expression::Value(location, hil::Value::from(value)),
+                warnings: vec![],
+                errors: vec![],
+            },
+
+            syntax::Expression::Reference(location, name) => match var_map.get_variable(&name) {
+                None => PassResult {
+                    result: hil::Expression::Reference(Location::Manufactured, 0),
+                    warnings: vec![],
+                    errors: vec![Error::UnboundVariable(location, name)],
+                },
+
+                Some(variable) => PassResult {
+                    result: hil::Expression::Reference(location, variable),
+                    warnings: vec![],
+                    errors: vec![],
+                },
+            }
+
+            syntax::Expression::Primitive(location, name, mut exprs) => {
+                let mut args = vec![];
+                let mut warnings = vec![];
+                let mut errors = vec![];
+
+                let op = match name.as_ref() {
+                    "+" => Primitive::Plus,
+                    "-" => Primitive::Minus,
+                    "*" => Primitive::Times,
+                    "/" => Primitive::Divide,
+                    other => {
+                        errors.push(Error::UnboundVariable(location.clone(), other.to_string()));
+                        Primitive::Plus
+                    }
+                };
+
+                for orig_expr in exprs.drain(..) {
+                    let mut sub_result = hil::Expression::convert(orig_expr, var_map);
+
+                    args.push(sub_result.result);
+                    warnings.append(&mut sub_result.warnings);
+                    errors.append(&mut sub_result.errors);
+                }
+
+                PassResult {
+                    result: hil::Expression::Primitive(location, op, args),
+                    warnings,
+                    errors,
+                }
+            }
+        }
+    }
+}
+
+impl From<syntax::Value> for hil::Value {
+    fn from(x: syntax::Value) -> hil::Value {
+        match x {
+            syntax::Value::Number(base, value) =>
+                hil::Value::Number(base, value),
+        }
+    }
+}
\ No newline at end of file
diff --git a/src/syntax.rs b/src/syntax.rs
index 0304fd4..62df280 100644
--- a/src/syntax.rs
+++ b/src/syntax.rs
@@ -38,13 +38,14 @@ impl FromStr for Program {
 
 #[test]
 fn order_of_operations() {
-    let muladd1 = "1 + 2 * 3;";
+    let muladd1 = "x = 1 + 2 * 3;";
     let testfile = 0;
     assert_eq!(
         Program::from_str(muladd1).unwrap(),
         Program {
-            statements: vec![Statement::Expr(
+            statements: vec![Statement::Binding(
                 Location::InFile(testfile, 0),
+                "x".to_string(),
                 Expression::Primitive(
                     Location::InFile(testfile, 2),
                     "+".to_string(),
diff --git a/src/syntax/ast.rs b/src/syntax/ast.rs
index 90f7d79..bdd9a13 100644
--- a/src/syntax/ast.rs
+++ b/src/syntax/ast.rs
@@ -31,7 +31,6 @@ where
 pub enum Statement {
     Binding(Location, String, Expression),
     Print(Location, String),
-    Expr(Location, Expression),
 }
 
 impl<'a, 'b, D, A> Pretty<'a, D, A> for &'b Statement
@@ -51,7 +50,6 @@ where
                 .text("print")
                 .append(allocator.space())
                 .append(allocator.text(var.to_string())),
-            Statement::Expr(_, expr) => expr.pretty(allocator),
         }
     }
 }
diff --git a/src/syntax/parser.lalrpop b/src/syntax/parser.lalrpop
index 2e34778..95fc2a5 100644
--- a/src/syntax/parser.lalrpop
+++ b/src/syntax/parser.lalrpop
@@ -43,8 +43,7 @@ Statements: Vec<Statement> = {
 
 Statement: Statement = {
     <l:@L> <v:"<var>"> "=" <e:Expression> ";" => Statement::Binding(l, v.to_string(), e),
-    <l:@L> "print" <v:"<var>"> ";" => Statement::Print(l, v.to_string()),
-    <l:@L> <e:Expression> ";" => Statement::Expr(l, e),
+    "print" <l:@L> <v:"<var>"> ";" => Statement::Print(l, v.to_string()),
 }
 
 Expression: Expression = {
diff --git a/src/variable_map.rs b/src/variable_map.rs
new file mode 100644
index 0000000..882bdd6
--- /dev/null
+++ b/src/variable_map.rs
@@ -0,0 +1,57 @@
+use crate::syntax::Location;
+use std::collections::HashMap;
+
+pub type Variable = usize;
+pub struct VariableMap {
+    map: HashMap<Variable, VariableInfo>,
+    next_index: Variable,
+}
+
+struct VariableInfo {
+    name: String,
+    binding_location: Location,
+}
+
+impl VariableInfo {
+    fn new(name: String, binding_location: Location) -> Self {
+        VariableInfo {
+            name,
+            binding_location,
+        }
+    }
+}
+
+impl VariableMap {
+    pub fn empty() -> Self {
+        VariableMap {
+            map: HashMap::new(),
+            next_index: 0,
+        }
+    }
+
+    pub fn add(&mut self, name: String, loc: Location) -> Variable {
+        let result = self.next_index;
+
+        self.next_index += 1;
+        self.map.insert(result, VariableInfo::new(name, loc));
+
+        result
+    }
+
+    pub fn get_name(&self, var: Variable) -> Option<&str> {
+        self.map.get(&var).map(|x| x.name.as_ref())
+    }
+
+    pub fn get_binding_site(&self, var: Variable) -> Option<Location> {
+        self.map.get(&var).map(|x| x.binding_location.clone())
+    }
+
+    pub fn get_variable(&self, name: &str) -> Option<usize> {
+        for (num, info) in self.map.iter() {
+            if info.name == name {
+                return Some(*num);
+            }
+        }
+        None
+    }
+}
diff --git a/src/warnings.rs b/src/warnings.rs
new file mode 100644
index 0000000..f76e712
--- /dev/null
+++ b/src/warnings.rs
@@ -0,0 +1,41 @@
+use crate::syntax::Location;
+use codespan_reporting::diagnostic::{Diagnostic, Label};
+
+#[derive(Debug, PartialEq)]
+pub enum Warning {
+    ShadowedVariable(Location, Location, String),
+}
+
+impl From<Warning> for Diagnostic<usize> {
+    fn from(x: Warning) -> Self {
+        match &x {
+            Warning::ShadowedVariable(original, new, name) => match original {
+                Location::Manufactured => match new {
+                    Location::Manufactured => Diagnostic::warning()
+                        .with_message(format!("Variable '{}' is rebound", name)),
+                    Location::InFile(file_id, offset) => Diagnostic::warning()
+                        .with_labels(vec![Label::primary(*file_id, *offset..*offset)
+                            .with_message("variable rebound here")])
+                        .with_message(format!("Variable '{}' is rebound", name)),
+                },
+                Location::InFile(orig_file_id, orig_offset) => match new {
+                    Location::Manufactured => Diagnostic::warning()
+                        .with_labels(vec![Label::primary(
+                            *orig_file_id,
+                            *orig_offset..*orig_offset,
+                        )
+                        .with_message("original binding site")])
+                        .with_message(format!("Variable '{}' is rebound", name)),
+                    Location::InFile(new_file_id, new_offset) => Diagnostic::warning()
+                        .with_labels(vec![
+                            Label::primary(*new_file_id, *new_offset..*new_offset)
+                                .with_message("variable rebound here"),
+                            Label::secondary(*orig_file_id, *orig_offset..*orig_offset)
+                                .with_message("original binding site"),
+                        ])
+                        .with_message(format!("Variable '{}' is rebound", name)),
+                },
+            },
+        }
+    }
+}