diff --git a/src/assignment.rs b/src/assignment.rs
index 20007d3..52c2e9c 100644
--- a/src/assignment.rs
+++ b/src/assignment.rs
@@ -1,18 +1,4 @@
 use crate::common::*;
 
 /// An assignment, e.g `foo := bar`
-#[derive(Debug, PartialEq)]
-pub(crate) struct Assignment<'src> {
-  /// Assignment was prefixed by the `export` keyword
-  pub(crate) export: bool,
-  /// Left-hand side of the assignment
-  pub(crate) name: Name<'src>,
-  /// Right-hand side of the assignment
-  pub(crate) expression: Expression<'src>,
-}
-
-impl<'src> Keyed<'src> for Assignment<'src> {
-  fn key(&self) -> &'src str {
-    self.name.lexeme()
-  }
-}
+pub(crate) type Assignment<'src> = Binding<'src, Expression<'src>>;
diff --git a/src/assignment_evaluator.rs b/src/assignment_evaluator.rs
deleted file mode 100644
index 6c99a1f..0000000
--- a/src/assignment_evaluator.rs
+++ /dev/null
@@ -1,231 +0,0 @@
-use crate::common::*;
-
-pub(crate) struct AssignmentEvaluator<'a: 'b, 'b> {
-  pub(crate) assignments: &'b Table<'a, Assignment<'a>>,
-  pub(crate) config: &'a Config,
-  pub(crate) dotenv: &'b BTreeMap<String, String>,
-  pub(crate) evaluated: BTreeMap<&'a str, (bool, String)>,
-  pub(crate) scope: &'b BTreeMap<&'a str, (bool, String)>,
-  pub(crate) working_directory: &'b Path,
-  pub(crate) overrides: &'b BTreeMap<String, String>,
-  pub(crate) settings: &'b Settings<'b>,
-}
-
-impl<'a, 'b> AssignmentEvaluator<'a, 'b> {
-  pub(crate) fn evaluate_assignments(
-    config: &'a Config,
-    working_directory: &'b Path,
-    dotenv: &'b BTreeMap<String, String>,
-    assignments: &Table<'a, Assignment<'a>>,
-    overrides: &BTreeMap<String, String>,
-    settings: &'b Settings<'b>,
-  ) -> RunResult<'a, BTreeMap<&'a str, (bool, String)>> {
-    let mut evaluator = AssignmentEvaluator {
-      evaluated: empty(),
-      scope: &empty(),
-      settings,
-      overrides,
-      config,
-      assignments,
-      working_directory,
-      dotenv,
-    };
-
-    for name in assignments.keys() {
-      evaluator.evaluate_assignment(name)?;
-    }
-
-    Ok(evaluator.evaluated)
-  }
-
-  pub(crate) fn evaluate_line(
-    &mut self,
-    line: &[Fragment<'a>],
-    arguments: &BTreeMap<&'a str, Cow<str>>,
-  ) -> RunResult<'a, String> {
-    let mut evaluated = String::new();
-    for fragment in line {
-      match fragment {
-        Fragment::Text { token } => evaluated += token.lexeme(),
-        Fragment::Interpolation { expression } => {
-          evaluated += &self.evaluate_expression(expression, arguments)?;
-        }
-      }
-    }
-    Ok(evaluated)
-  }
-
-  fn evaluate_assignment(&mut self, name: &'a str) -> RunResult<'a, ()> {
-    if self.evaluated.contains_key(name) {
-      return Ok(());
-    }
-
-    if let Some(assignment) = self.assignments.get(name) {
-      if let Some(value) = self.overrides.get(name) {
-        self
-          .evaluated
-          .insert(name, (assignment.export, value.to_string()));
-      } else {
-        let value = self.evaluate_expression(&assignment.expression, &empty())?;
-        self.evaluated.insert(name, (assignment.export, value));
-      }
-    } else {
-      return Err(RuntimeError::Internal {
-        message: format!("attempted to evaluated unknown assignment {}", name),
-      });
-    }
-
-    Ok(())
-  }
-
-  pub(crate) fn evaluate_expression(
-    &mut self,
-    expression: &Expression<'a>,
-    arguments: &BTreeMap<&'a str, Cow<str>>,
-  ) -> RunResult<'a, String> {
-    match expression {
-      Expression::Variable { name, .. } => {
-        let variable = name.lexeme();
-        if self.evaluated.contains_key(variable) {
-          Ok(self.evaluated[variable].1.clone())
-        } else if self.scope.contains_key(variable) {
-          Ok(self.scope[variable].1.clone())
-        } else if self.assignments.contains_key(variable) {
-          self.evaluate_assignment(variable)?;
-          Ok(self.evaluated[variable].1.clone())
-        } else if arguments.contains_key(variable) {
-          Ok(arguments[variable].to_string())
-        } else {
-          Err(RuntimeError::Internal {
-            message: format!("attempted to evaluate undefined variable `{}`", variable),
-          })
-        }
-      }
-      Expression::Call { thunk } => {
-        let context = FunctionContext {
-          invocation_directory: &self.config.invocation_directory,
-          working_directory: &self.working_directory,
-          dotenv: self.dotenv,
-        };
-
-        use Thunk::*;
-        match thunk {
-          Nullary { name, function, .. } => {
-            function(&context).map_err(|message| RuntimeError::FunctionCall {
-              function: *name,
-              message,
-            })
-          }
-          Unary {
-            name,
-            function,
-            arg,
-            ..
-          } => function(&context, &self.evaluate_expression(arg, arguments)?).map_err(|message| {
-            RuntimeError::FunctionCall {
-              function: *name,
-              message,
-            }
-          }),
-          Binary {
-            name,
-            function,
-            args: [a, b],
-            ..
-          } => function(
-            &context,
-            &self.evaluate_expression(a, arguments)?,
-            &self.evaluate_expression(b, arguments)?,
-          )
-          .map_err(|message| RuntimeError::FunctionCall {
-            function: *name,
-            message,
-          }),
-        }
-      }
-      Expression::StringLiteral { string_literal } => Ok(string_literal.cooked.to_string()),
-      Expression::Backtick { contents, token } => {
-        if self.config.dry_run {
-          Ok(format!("`{}`", contents))
-        } else {
-          Ok(self.run_backtick(self.dotenv, contents, token)?)
-        }
-      }
-      Expression::Concatination { lhs, rhs } => {
-        Ok(self.evaluate_expression(lhs, arguments)? + &self.evaluate_expression(rhs, arguments)?)
-      }
-      Expression::Group { contents } => self.evaluate_expression(contents, arguments),
-    }
-  }
-
-  fn run_backtick(
-    &self,
-    dotenv: &BTreeMap<String, String>,
-    raw: &str,
-    token: &Token<'a>,
-  ) -> RunResult<'a, String> {
-    let mut cmd = self.settings.shell_command(self.config);
-
-    cmd.arg(raw);
-
-    cmd.current_dir(self.working_directory);
-
-    cmd.export_environment_variables(self.scope, dotenv)?;
-
-    cmd.stdin(process::Stdio::inherit());
-
-    cmd.stderr(if self.config.quiet {
-      process::Stdio::null()
-    } else {
-      process::Stdio::inherit()
-    });
-
-    InterruptHandler::guard(|| {
-      output(cmd).map_err(|output_error| RuntimeError::Backtick {
-        token: *token,
-        output_error,
-      })
-    })
-  }
-}
-
-#[cfg(test)]
-mod tests {
-  use super::*;
-
-  run_error! {
-    name: backtick_code,
-    src: "
-      a:
-       echo {{`f() { return 100; }; f`}}
-    ",
-    args: ["a"],
-    error: RuntimeError::Backtick {
-      token,
-      output_error: OutputError::Code(code),
-    },
-    check: {
-      assert_eq!(code, 100);
-      assert_eq!(token.lexeme(), "`f() { return 100; }; f`");
-    }
-  }
-
-  run_error! {
-    name: export_assignment_backtick,
-    src: r#"
-      export exported_variable = "A"
-      b = `echo $exported_variable`
-
-      recipe:
-        echo {{b}}
-    "#,
-    args: ["--quiet", "recipe"],
-    error: RuntimeError::Backtick {
-        token,
-        output_error: OutputError::Code(_),
-    },
-    check: {
-      assert_eq!(token.lexeme(), "`echo $exported_variable`");
-    }
-  }
-}
diff --git a/src/assignment_resolver.rs b/src/assignment_resolver.rs
index b172e35..92142be 100644
--- a/src/assignment_resolver.rs
+++ b/src/assignment_resolver.rs
@@ -2,17 +2,17 @@ use crate::common::*;
 
 use CompilationErrorKind::*;
 
-pub(crate) struct AssignmentResolver<'a: 'b, 'b> {
-  assignments: &'b Table<'a, Assignment<'a>>,
-  stack: Vec<&'a str>,
-  seen: BTreeSet<&'a str>,
-  evaluated: BTreeSet<&'a str>,
+pub(crate) struct AssignmentResolver<'src: 'run, 'run> {
+  assignments: &'run Table<'src, Assignment<'src>>,
+  stack: Vec<&'src str>,
+  seen: BTreeSet<&'src str>,
+  evaluated: BTreeSet<&'src str>,
 }
 
-impl<'a: 'b, 'b> AssignmentResolver<'a, 'b> {
+impl<'src: 'run, 'run> AssignmentResolver<'src, 'run> {
   pub(crate) fn resolve_assignments(
-    assignments: &Table<'a, Assignment<'a>>,
-  ) -> CompilationResult<'a, ()> {
+    assignments: &Table<'src, Assignment<'src>>,
+  ) -> CompilationResult<'src, ()> {
     let mut resolver = AssignmentResolver {
       stack: empty(),
       seen: empty(),
@@ -27,7 +27,7 @@ impl<'a: 'b, 'b> AssignmentResolver<'a, 'b> {
     Ok(())
   }
 
-  fn resolve_assignment(&mut self, name: &'a str) -> CompilationResult<'a, ()> {
+  fn resolve_assignment(&mut self, name: &'src str) -> CompilationResult<'src, ()> {
     if self.evaluated.contains(name) {
       return Ok(());
     }
@@ -36,7 +36,7 @@ impl<'a: 'b, 'b> AssignmentResolver<'a, 'b> {
     self.stack.push(name);
 
     if let Some(assignment) = self.assignments.get(name) {
-      self.resolve_expression(&assignment.expression)?;
+      self.resolve_expression(&assignment.value)?;
       self.evaluated.insert(name);
     } else {
       let message = format!("attempted to resolve unknown assignment `{}`", name);
@@ -56,7 +56,7 @@ impl<'a: 'b, 'b> AssignmentResolver<'a, 'b> {
     Ok(())
   }
 
-  fn resolve_expression(&mut self, expression: &Expression<'a>) -> CompilationResult<'a, ()> {
+  fn resolve_expression(&mut self, expression: &Expression<'src>) -> CompilationResult<'src, ()> {
     match expression {
       Expression::Variable { name } => {
         let variable = name.lexeme();
diff --git a/src/binding.rs b/src/binding.rs
new file mode 100644
index 0000000..5b993c5
--- /dev/null
+++ b/src/binding.rs
@@ -0,0 +1,18 @@
+use crate::common::*;
+
+/// A binding of `name` to `value`
+#[derive(Debug, PartialEq)]
+pub(crate) struct Binding<'src, V = String> {
+  /// Export binding as an environment variable to child processes
+  pub(crate) export: bool,
+  /// Binding name
+  pub(crate) name: Name<'src>,
+  /// Binding value
+  pub(crate) value: V,
+}
+
+impl<'src, V> Keyed<'src> for Binding<'src, V> {
+  fn key(&self) -> &'src str {
+    self.name.lexeme()
+  }
+}
diff --git a/src/command_ext.rs b/src/command_ext.rs
index e17d797..1568ae5 100644
--- a/src/command_ext.rs
+++ b/src/command_ext.rs
@@ -1,29 +1,31 @@
 use crate::common::*;
 
 pub(crate) trait CommandExt {
-  fn export_environment_variables<'a>(
-    &mut self,
-    scope: &BTreeMap<&'a str, (bool, String)>,
-    dotenv: &BTreeMap<String, String>,
-  ) -> RunResult<'a, ()>;
+  fn export(&mut self, dotenv: &BTreeMap<String, String>, scope: &Scope);
+
+  fn export_scope(&mut self, scope: &Scope);
 }
 
 impl CommandExt for Command {
-  fn export_environment_variables<'a>(
-    &mut self,
-    scope: &BTreeMap<&'a str, (bool, String)>,
-    dotenv: &BTreeMap<String, String>,
-  ) -> RunResult<'a, ()> {
+  fn export(&mut self, dotenv: &BTreeMap<String, String>, scope: &Scope) {
     for (name, value) in dotenv {
       self.env(name, value);
     }
 
-    for (name, (export, value)) in scope {
-      if *export {
-        self.env(name, value);
-      }
+    if let Some(parent) = scope.parent() {
+      self.export_scope(parent);
+    }
+  }
+
+  fn export_scope(&mut self, scope: &Scope) {
+    if let Some(parent) = scope.parent() {
+      self.export_scope(parent);
     }
 
-    Ok(())
+    for binding in scope.bindings() {
+      if binding.export {
+        self.env(binding.name.lexeme(), &binding.value);
+      }
+    }
   }
 }
diff --git a/src/common.rs b/src/common.rs
index 0074a20..98dd3f9 100644
--- a/src/common.rs
+++ b/src/common.rs
@@ -49,16 +49,16 @@ pub(crate) use crate::{
 // structs and enums
 pub(crate) use crate::{
   alias::Alias, analyzer::Analyzer, assignment::Assignment,
-  assignment_evaluator::AssignmentEvaluator, assignment_resolver::AssignmentResolver, color::Color,
+  assignment_resolver::AssignmentResolver, binding::Binding, color::Color,
   compilation_error::CompilationError, compilation_error_kind::CompilationErrorKind,
   compiler::Compiler, config::Config, config_error::ConfigError, count::Count,
-  dependency::Dependency, enclosure::Enclosure, expression::Expression, fragment::Fragment,
-  function::Function, function_context::FunctionContext, interrupt_guard::InterruptGuard,
-  interrupt_handler::InterruptHandler, item::Item, justfile::Justfile, lexer::Lexer, line::Line,
-  list::List, load_error::LoadError, module::Module, name::Name, output_error::OutputError,
-  parameter::Parameter, parser::Parser, platform::Platform, position::Position,
-  positional::Positional, recipe::Recipe, recipe_context::RecipeContext,
-  recipe_resolver::RecipeResolver, runtime_error::RuntimeError, search::Search,
+  dependency::Dependency, enclosure::Enclosure, evaluator::Evaluator, expression::Expression,
+  fragment::Fragment, function::Function, function_context::FunctionContext,
+  interrupt_guard::InterruptGuard, interrupt_handler::InterruptHandler, item::Item,
+  justfile::Justfile, lexer::Lexer, line::Line, list::List, load_error::LoadError, module::Module,
+  name::Name, output_error::OutputError, parameter::Parameter, parser::Parser, platform::Platform,
+  position::Position, positional::Positional, recipe::Recipe, recipe_context::RecipeContext,
+  recipe_resolver::RecipeResolver, runtime_error::RuntimeError, scope::Scope, search::Search,
   search_config::SearchConfig, search_error::SearchError, set::Set, setting::Setting,
   settings::Settings, shebang::Shebang, show_whitespace::ShowWhitespace, state::State,
   string_literal::StringLiteral, subcommand::Subcommand, table::Table, thunk::Thunk, token::Token,
diff --git a/src/compilation_error_kind.rs b/src/compilation_error_kind.rs
index a89dd37..4a3a9fb 100644
--- a/src/compilation_error_kind.rs
+++ b/src/compilation_error_kind.rs
@@ -1,55 +1,55 @@
 use crate::common::*;
 
 #[derive(Debug, PartialEq)]
-pub(crate) enum CompilationErrorKind<'a> {
+pub(crate) enum CompilationErrorKind<'src> {
   AliasShadowsRecipe {
-    alias: &'a str,
+    alias: &'src str,
     recipe_line: usize,
   },
   CircularRecipeDependency {
-    recipe: &'a str,
-    circle: Vec<&'a str>,
+    recipe: &'src str,
+    circle: Vec<&'src str>,
   },
   CircularVariableDependency {
-    variable: &'a str,
-    circle: Vec<&'a str>,
+    variable: &'src str,
+    circle: Vec<&'src str>,
   },
   DependencyHasParameters {
-    recipe: &'a str,
-    dependency: &'a str,
+    recipe: &'src str,
+    dependency: &'src str,
   },
   DuplicateAlias {
-    alias: &'a str,
+    alias: &'src str,
     first: usize,
   },
   DuplicateDependency {
-    recipe: &'a str,
-    dependency: &'a str,
+    recipe: &'src str,
+    dependency: &'src str,
   },
   DuplicateParameter {
-    recipe: &'a str,
-    parameter: &'a str,
+    recipe: &'src str,
+    parameter: &'src str,
   },
   DuplicateRecipe {
-    recipe: &'a str,
+    recipe: &'src str,
     first: usize,
   },
   DuplicateVariable {
-    variable: &'a str,
+    variable: &'src str,
   },
   DuplicateSet {
-    setting: &'a str,
+    setting: &'src str,
     first: usize,
   },
   ExtraLeadingWhitespace,
   FunctionArgumentCountMismatch {
-    function: &'a str,
+    function: &'src str,
     found: usize,
     expected: usize,
   },
   InconsistentLeadingWhitespace {
-    expected: &'a str,
-    found: &'a str,
+    expected: &'src str,
+    found: &'src str,
   },
   Internal {
     message: String,
@@ -58,38 +58,38 @@ pub(crate) enum CompilationErrorKind<'a> {
     character: char,
   },
   MixedLeadingWhitespace {
-    whitespace: &'a str,
+    whitespace: &'src str,
   },
   ParameterFollowsVariadicParameter {
-    parameter: &'a str,
+    parameter: &'src str,
   },
   ParameterShadowsVariable {
-    parameter: &'a str,
+    parameter: &'src str,
   },
   RequiredParameterFollowsDefaultParameter {
-    parameter: &'a str,
+    parameter: &'src str,
   },
   UndefinedVariable {
-    variable: &'a str,
+    variable: &'src str,
   },
   UnexpectedToken {
     expected: Vec<TokenKind>,
     found: TokenKind,
   },
   UnknownAliasTarget {
-    alias: &'a str,
-    target: &'a str,
+    alias: &'src str,
+    target: &'src str,
   },
   UnknownDependency {
-    recipe: &'a str,
-    unknown: &'a str,
+    recipe: &'src str,
+    unknown: &'src str,
   },
   UnknownFunction {
-    function: &'a str,
+    function: &'src str,
   },
   UnknownStartOfToken,
   UnknownSetting {
-    setting: &'a str,
+    setting: &'src str,
   },
   UnpairedCarriageReturn,
   UnterminatedInterpolation,
diff --git a/src/dependency.rs b/src/dependency.rs
index 113db96..38c9712 100644
--- a/src/dependency.rs
+++ b/src/dependency.rs
@@ -1,4 +1,4 @@
 use crate::common::*;
 
 #[derive(PartialEq, Debug)]
-pub(crate) struct Dependency<'a>(pub(crate) Rc<Recipe<'a>>);
+pub(crate) struct Dependency<'src>(pub(crate) Rc<Recipe<'src>>);
diff --git a/src/evaluator.rs b/src/evaluator.rs
new file mode 100644
index 0000000..5586b5d
--- /dev/null
+++ b/src/evaluator.rs
@@ -0,0 +1,266 @@
+use crate::common::*;
+
+pub(crate) struct Evaluator<'src: 'run, 'run> {
+  assignments: Option<&'run Table<'src, Assignment<'src>>>,
+  config: &'run Config,
+  dotenv: &'run BTreeMap<String, String>,
+  scope: Scope<'src, 'run>,
+  settings: &'run Settings<'run>,
+  working_directory: &'run Path,
+}
+
+impl<'src, 'run> Evaluator<'src, 'run> {
+  pub(crate) fn evaluate_assignments(
+    assignments: &'run Table<'src, Assignment<'src>>,
+    config: &'run Config,
+    dotenv: &'run BTreeMap<String, String>,
+    overrides: Scope<'src, 'run>,
+    settings: &'run Settings<'run>,
+    working_directory: &'run Path,
+  ) -> RunResult<'src, Scope<'src, 'run>> {
+    let mut evaluator = Evaluator {
+      scope: overrides,
+      assignments: Some(assignments),
+      config,
+      dotenv,
+      settings,
+      working_directory,
+    };
+
+    for assignment in assignments.values() {
+      evaluator.evaluate_assignment(assignment)?;
+    }
+
+    Ok(evaluator.scope)
+  }
+
+  fn evaluate_assignment(&mut self, assignment: &Assignment<'src>) -> RunResult<'src, &str> {
+    let name = assignment.name.lexeme();
+
+    if !self.scope.bound(name) {
+      let value = self.evaluate_expression(&assignment.value)?;
+      self.scope.bind(assignment.export, assignment.name, value);
+    }
+
+    Ok(self.scope.value(name).unwrap())
+  }
+
+  pub(crate) fn evaluate_expression(
+    &mut self,
+    expression: &Expression<'src>,
+  ) -> RunResult<'src, String> {
+    match expression {
+      Expression::Variable { name, .. } => {
+        let variable = name.lexeme();
+        if let Some(value) = self.scope.value(variable) {
+          Ok(value.to_owned())
+        } else if let Some(assignment) = self
+          .assignments
+          .and_then(|assignments| assignments.get(variable))
+        {
+          Ok(self.evaluate_assignment(assignment)?.to_owned())
+        } else {
+          Err(RuntimeError::Internal {
+            message: format!("attempted to evaluate undefined variable `{}`", variable),
+          })
+        }
+      }
+      Expression::Call { thunk } => {
+        let context = FunctionContext {
+          invocation_directory: &self.config.invocation_directory,
+          working_directory: &self.working_directory,
+          dotenv: self.dotenv,
+        };
+
+        use Thunk::*;
+        match thunk {
+          Nullary { name, function, .. } => {
+            function(&context).map_err(|message| RuntimeError::FunctionCall {
+              function: *name,
+              message,
+            })
+          }
+          Unary {
+            name,
+            function,
+            arg,
+            ..
+          } => function(&context, &self.evaluate_expression(arg)?).map_err(|message| {
+            RuntimeError::FunctionCall {
+              function: *name,
+              message,
+            }
+          }),
+          Binary {
+            name,
+            function,
+            args: [a, b],
+            ..
+          } => function(
+            &context,
+            &self.evaluate_expression(a)?,
+            &self.evaluate_expression(b)?,
+          )
+          .map_err(|message| RuntimeError::FunctionCall {
+            function: *name,
+            message,
+          }),
+        }
+      }
+      Expression::StringLiteral { string_literal } => Ok(string_literal.cooked.to_string()),
+      Expression::Backtick { contents, token } => {
+        if self.config.dry_run {
+          Ok(format!("`{}`", contents))
+        } else {
+          Ok(self.run_backtick(contents, token)?)
+        }
+      }
+      Expression::Concatination { lhs, rhs } => {
+        Ok(self.evaluate_expression(lhs)? + &self.evaluate_expression(rhs)?)
+      }
+      Expression::Group { contents } => self.evaluate_expression(contents),
+    }
+  }
+
+  fn run_backtick(&self, raw: &str, token: &Token<'src>) -> RunResult<'src, String> {
+    let mut cmd = self.settings.shell_command(self.config);
+
+    cmd.arg(raw);
+
+    cmd.current_dir(self.working_directory);
+
+    cmd.export(self.dotenv, &self.scope);
+
+    cmd.stdin(process::Stdio::inherit());
+
+    cmd.stderr(if self.config.quiet {
+      process::Stdio::null()
+    } else {
+      process::Stdio::inherit()
+    });
+
+    InterruptHandler::guard(|| {
+      output(cmd).map_err(|output_error| RuntimeError::Backtick {
+        token: *token,
+        output_error,
+      })
+    })
+  }
+
+  pub(crate) fn evaluate_line(&mut self, line: &Line<'src>) -> RunResult<'src, String> {
+    let mut evaluated = String::new();
+    for fragment in &line.fragments {
+      match fragment {
+        Fragment::Text { token } => evaluated += token.lexeme(),
+        Fragment::Interpolation { expression } => {
+          evaluated += &self.evaluate_expression(expression)?;
+        }
+      }
+    }
+    Ok(evaluated)
+  }
+
+  pub(crate) fn evaluate_parameters(
+    config: &'run Config,
+    dotenv: &'run BTreeMap<String, String>,
+    parameters: &[Parameter<'src>],
+    arguments: &[&str],
+    scope: &'run Scope<'src, 'run>,
+    settings: &'run Settings,
+    working_directory: &'run Path,
+  ) -> RunResult<'src, Scope<'src, 'run>> {
+    let mut evaluator = Evaluator {
+      assignments: None,
+      scope: Scope::child(scope),
+      settings,
+      dotenv,
+      config,
+      working_directory,
+    };
+
+    let mut scope = Scope::child(scope);
+
+    let mut rest = arguments;
+    for parameter in parameters {
+      let value = if rest.is_empty() {
+        match parameter.default {
+          Some(ref default) => evaluator.evaluate_expression(default)?,
+          None => {
+            return Err(RuntimeError::Internal {
+              message: "missing parameter without default".to_string(),
+            });
+          }
+        }
+      } else if parameter.variadic {
+        let value = rest.to_vec().join(" ");
+        rest = &[];
+        value
+      } else {
+        let value = rest[0].to_owned();
+        rest = &rest[1..];
+        value
+      };
+      scope.bind(false, parameter.name, value);
+    }
+
+    Ok(scope)
+  }
+
+  pub(crate) fn line_evaluator(
+    config: &'run Config,
+    dotenv: &'run BTreeMap<String, String>,
+    scope: &'run Scope<'src, 'run>,
+    settings: &'run Settings,
+    working_directory: &'run Path,
+  ) -> Evaluator<'src, 'run> {
+    Evaluator {
+      assignments: None,
+      scope: Scope::child(scope),
+      settings,
+      dotenv,
+      config,
+      working_directory,
+    }
+  }
+}
+
+#[cfg(test)]
+mod tests {
+  use super::*;
+
+  run_error! {
+    name: backtick_code,
+    src: "
+      a:
+       echo {{`f() { return 100; }; f`}}
+    ",
+    args: ["a"],
+    error: RuntimeError::Backtick {
+      token,
+      output_error: OutputError::Code(code),
+    },
+    check: {
+      assert_eq!(code, 100);
+      assert_eq!(token.lexeme(), "`f() { return 100; }; f`");
+    }
+  }
+
+  run_error! {
+    name: export_assignment_backtick,
+    src: r#"
+      export exported_variable = "A"
+      b = `echo $exported_variable`
+
+      recipe:
+        echo {{b}}
+    "#,
+    args: ["--quiet", "recipe"],
+    error: RuntimeError::Backtick {
+        token,
+        output_error: OutputError::Code(_),
+    },
+    check: {
+      assert_eq!(token.lexeme(), "`echo $exported_variable`");
+    }
+  }
+}
diff --git a/src/function_context.rs b/src/function_context.rs
index cc48df7..074b148 100644
--- a/src/function_context.rs
+++ b/src/function_context.rs
@@ -1,7 +1,7 @@
 use crate::common::*;
 
-pub(crate) struct FunctionContext<'a> {
-  pub(crate) invocation_directory: &'a Path,
-  pub(crate) working_directory: &'a Path,
-  pub(crate) dotenv: &'a BTreeMap<String, String>,
+pub(crate) struct FunctionContext<'run> {
+  pub(crate) invocation_directory: &'run Path,
+  pub(crate) working_directory: &'run Path,
+  pub(crate) dotenv: &'run BTreeMap<String, String>,
 }
diff --git a/src/justfile.rs b/src/justfile.rs
index 594bf51..ae5a6a2 100644
--- a/src/justfile.rs
+++ b/src/justfile.rs
@@ -81,23 +81,48 @@ impl<'src> Justfile<'src> {
 
     let dotenv = load_dotenv()?;
 
-    let scope = AssignmentEvaluator::evaluate_assignments(
-      config,
-      working_directory,
-      &dotenv,
-      &self.assignments,
-      overrides,
-      &self.settings,
-    )?;
+    let scope = {
+      let mut scope = Scope::new();
+      let mut unknown_overrides = Vec::new();
+
+      for (name, value) in overrides {
+        if let Some(assignment) = self.assignments.get(name) {
+          scope.bind(assignment.export, assignment.name, value.clone());
+        } else {
+          unknown_overrides.push(name.as_ref());
+        }
+      }
+
+      if !unknown_overrides.is_empty() {
+        return Err(RuntimeError::UnknownOverrides {
+          overrides: unknown_overrides,
+        });
+      }
+
+      Evaluator::evaluate_assignments(
+        &self.assignments,
+        config,
+        &dotenv,
+        scope,
+        &self.settings,
+        working_directory,
+      )?
+    };
 
     if let Subcommand::Evaluate { .. } = config.subcommand {
       let mut width = 0;
-      for name in scope.keys() {
+
+      for name in scope.names() {
         width = cmp::max(name.len(), width);
       }
 
-      for (name, (_export, value)) in scope {
-        println!("{0:1$} := \"{2}\"", name, width, value);
+      for binding in scope.bindings() {
+        println!(
+          "{0:1$} := \"{2}\"",
+          binding.name.lexeme(),
+          width,
+          binding.value
+        );
       }
       return Ok(());
     }
@@ -152,7 +177,7 @@ impl<'src> Justfile<'src> {
 
     let mut ran = empty();
     for (recipe, arguments) in grouped {
-      self.run_recipe(&context, recipe, arguments, &dotenv, &mut ran, overrides)?
+      self.run_recipe(&context, recipe, arguments, &dotenv, &mut ran)?
     }
 
     Ok(())
@@ -172,21 +197,20 @@ impl<'src> Justfile<'src> {
     }
   }
 
-  fn run_recipe<'b>(
+  fn run_recipe<'run>(
     &self,
-    context: &'b RecipeContext<'src>,
+    context: &'run RecipeContext<'src, 'run>,
     recipe: &Recipe<'src>,
     arguments: &[&'src str],
     dotenv: &BTreeMap<String, String>,
     ran: &mut BTreeSet<&'src str>,
-    overrides: &BTreeMap<String, String>,
-  ) -> RunResult<()> {
+  ) -> RunResult<'src, ()> {
     for Dependency(dependency) in &recipe.dependencies {
       if !ran.contains(dependency.name()) {
-        self.run_recipe(context, dependency, &[], dotenv, ran, overrides)?;
+        self.run_recipe(context, dependency, &[], dotenv, ran)?;
       }
     }
-    recipe.run(context, arguments, dotenv, overrides)?;
+    recipe.run(context, arguments, dotenv)?;
     ran.insert(recipe.name());
     Ok(())
   }
@@ -199,7 +223,7 @@ impl<'src> Display for Justfile<'src> {
       if assignment.export {
         write!(f, "export ")?;
       }
-      write!(f, "{} := {}", name, assignment.expression)?;
+      write!(f, "{} := {}", name, assignment.value)?;
       items -= 1;
       if items != 0 {
         write!(f, "\n\n")?;
diff --git a/src/lib.rs b/src/lib.rs
index 8513971..55b6090 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -18,8 +18,8 @@ pub(crate) mod fuzzing;
 mod alias;
 mod analyzer;
 mod assignment;
-mod assignment_evaluator;
 mod assignment_resolver;
+mod binding;
 mod color;
 mod command_ext;
 mod common;
@@ -36,6 +36,7 @@ mod empty;
 mod enclosure;
 mod error;
 mod error_result_ext;
+mod evaluator;
 mod expression;
 mod fragment;
 mod function;
@@ -68,6 +69,7 @@ mod recipe_context;
 mod recipe_resolver;
 mod run;
 mod runtime_error;
+mod scope;
 mod search;
 mod search_config;
 mod search_error;
diff --git a/src/node.rs b/src/node.rs
index e7a63ca..cc4bed5 100644
--- a/src/node.rs
+++ b/src/node.rs
@@ -42,7 +42,7 @@ impl<'src> Node<'src> for Assignment<'src> {
       Tree::atom("assignment")
     }
     .push(self.name.lexeme())
-    .push(self.expression.tree())
+    .push(self.value.tree())
   }
 }
 
diff --git a/src/parser.rs b/src/parser.rs
index 5f35005..5744048 100644
--- a/src/parser.rs
+++ b/src/parser.rs
@@ -338,12 +338,12 @@ impl<'tokens, 'src> Parser<'tokens, 'src> {
   fn parse_assignment(&mut self, export: bool) -> CompilationResult<'src, Assignment<'src>> {
     let name = self.parse_name()?;
     self.presume_any(&[Equals, ColonEquals])?;
-    let expression = self.parse_expression()?;
+    let value = self.parse_expression()?;
     self.expect_eol()?;
     Ok(Assignment {
       name,
       export,
-      expression,
+      value,
     })
   }
 
diff --git a/src/recipe.rs b/src/recipe.rs
index 250dca8..7a872e3 100644
--- a/src/recipe.rs
+++ b/src/recipe.rs
@@ -24,18 +24,18 @@ fn error_from_signal(
 
 /// A recipe, e.g. `foo: bar baz`
 #[derive(PartialEq, Debug)]
-pub(crate) struct Recipe<'a, D = Dependency<'a>> {
+pub(crate) struct Recipe<'src, D = Dependency<'src>> {
   pub(crate) dependencies: Vec<D>,
-  pub(crate) doc: Option<&'a str>,
-  pub(crate) body: Vec<Line<'a>>,
-  pub(crate) name: Name<'a>,
-  pub(crate) parameters: Vec<Parameter<'a>>,
+  pub(crate) doc: Option<&'src str>,
+  pub(crate) body: Vec<Line<'src>>,
+  pub(crate) name: Name<'src>,
+  pub(crate) parameters: Vec<Parameter<'src>>,
   pub(crate) private: bool,
   pub(crate) quiet: bool,
   pub(crate) shebang: bool,
 }
 
-impl<'a, D> Recipe<'a, D> {
+impl<'src, D> Recipe<'src, D> {
   pub(crate) fn argument_range(&self) -> RangeInclusive<usize> {
     self.min_arguments()..=self.max_arguments()
   }
@@ -56,7 +56,7 @@ impl<'a, D> Recipe<'a, D> {
     }
   }
 
-  pub(crate) fn name(&self) -> &'a str {
+  pub(crate) fn name(&self) -> &'src str {
     self.name.lexeme()
   }
 
@@ -64,13 +64,12 @@ impl<'a, D> Recipe<'a, D> {
     self.name.line
   }
 
-  pub(crate) fn run(
+  pub(crate) fn run<'run>(
     &self,
-    context: &RecipeContext<'a>,
-    arguments: &[&'a str],
+    context: &RecipeContext<'src, 'run>,
+    arguments: &[&'src str],
     dotenv: &BTreeMap<String, String>,
-    overrides: &BTreeMap<String, String>,
-  ) -> RunResult<'a, ()> {
+  ) -> RunResult<'src, ()> {
     let config = &context.config;
 
     if config.verbosity.loquacious() {
@@ -83,46 +82,28 @@ impl<'a, D> Recipe<'a, D> {
       );
     }
 
-    let mut argument_map = BTreeMap::new();
-
-    let mut evaluator = AssignmentEvaluator {
-      assignments: &empty(),
-      evaluated: empty(),
-      working_directory: context.working_directory,
-      scope: &context.scope,
-      settings: &context.settings,
-      overrides,
-      config,
+    let scope = Evaluator::evaluate_parameters(
+      context.config,
       dotenv,
-    };
+      &self.parameters,
+      arguments,
+      &context.scope,
+      context.settings,
+      context.working_directory,
+    )?;
 
-    let mut rest = arguments;
-    for parameter in &self.parameters {
-      let value = if rest.is_empty() {
-        match parameter.default {
-          Some(ref default) => Cow::Owned(evaluator.evaluate_expression(default, &empty())?),
-          None => {
-            return Err(RuntimeError::Internal {
-              message: "missing parameter without default".to_string(),
-            });
-          }
-        }
-      } else if parameter.variadic {
-        let value = Cow::Owned(rest.to_vec().join(" "));
-        rest = &[];
-        value
-      } else {
-        let value = Cow::Borrowed(rest[0]);
-        rest = &rest[1..];
-        value
-      };
-      argument_map.insert(parameter.name.lexeme(), value);
-    }
+    let mut evaluator = Evaluator::line_evaluator(
+      context.config,
+      dotenv,
+      &scope,
+      context.settings,
+      context.working_directory,
+    );
 
     if self.shebang {
       let mut evaluated_lines = vec![];
       for line in &self.body {
-        evaluated_lines.push(evaluator.evaluate_line(&line.fragments, &argument_map)?);
+        evaluated_lines.push(evaluator.evaluate_line(line)?);
       }
 
       if config.dry_run || self.quiet {
@@ -202,7 +183,7 @@ impl<'a, D> Recipe<'a, D> {
             output_error,
           })?;
 
-      command.export_environment_variables(&context.scope, dotenv)?;
+      command.export(dotenv, &scope);
 
       // run it!
       match InterruptHandler::guard(|| command.status()) {
@@ -242,7 +223,7 @@ impl<'a, D> Recipe<'a, D> {
           }
           let line = lines.next().unwrap();
           line_number += 1;
-          evaluated += &evaluator.evaluate_line(&line.fragments, &argument_map)?;
+          evaluated += &evaluator.evaluate_line(line)?;
           if line.is_continuation() {
             evaluated.pop();
           } else {
@@ -286,7 +267,7 @@ impl<'a, D> Recipe<'a, D> {
           cmd.stdout(Stdio::null());
         }
 
-        cmd.export_environment_variables(&context.scope, dotenv)?;
+        cmd.export(dotenv, &scope);
 
         match InterruptHandler::guard(|| cmd.status()) {
           Ok(exit_status) => {
@@ -344,7 +325,7 @@ impl<'src, D> Keyed<'src> for Recipe<'src, D> {
   }
 }
 
-impl<'a> Display for Recipe<'a> {
+impl<'src> Display for Recipe<'src> {
   fn fmt(&self, f: &mut Formatter) -> Result<(), fmt::Error> {
     if let Some(doc) = self.doc {
       writeln!(f, "# {}", doc)?;
diff --git a/src/recipe_context.rs b/src/recipe_context.rs
index 7c45b2c..8e3abbb 100644
--- a/src/recipe_context.rs
+++ b/src/recipe_context.rs
@@ -1,8 +1,8 @@
 use crate::common::*;
 
-pub(crate) struct RecipeContext<'a> {
-  pub(crate) config: &'a Config,
-  pub(crate) scope: BTreeMap<&'a str, (bool, String)>,
-  pub(crate) working_directory: &'a Path,
-  pub(crate) settings: &'a Settings<'a>,
+pub(crate) struct RecipeContext<'src: 'run, 'run> {
+  pub(crate) config: &'run Config,
+  pub(crate) scope: Scope<'src, 'run>,
+  pub(crate) working_directory: &'run Path,
+  pub(crate) settings: &'run Settings<'src>,
 }
diff --git a/src/recipe_resolver.rs b/src/recipe_resolver.rs
index 3fcde9a..91fb9fc 100644
--- a/src/recipe_resolver.rs
+++ b/src/recipe_resolver.rs
@@ -2,17 +2,17 @@ use crate::common::*;
 
 use CompilationErrorKind::*;
 
-pub(crate) struct RecipeResolver<'a: 'b, 'b> {
-  unresolved_recipes: Table<'a, Recipe<'a, Name<'a>>>,
-  resolved_recipes: Table<'a, Rc<Recipe<'a>>>,
-  assignments: &'b Table<'a, Assignment<'a>>,
+pub(crate) struct RecipeResolver<'src: 'run, 'run> {
+  unresolved_recipes: Table<'src, Recipe<'src, Name<'src>>>,
+  resolved_recipes: Table<'src, Rc<Recipe<'src>>>,
+  assignments: &'run Table<'src, Assignment<'src>>,
 }
 
-impl<'a, 'b> RecipeResolver<'a, 'b> {
+impl<'src: 'run, 'run> RecipeResolver<'src, 'run> {
   pub(crate) fn resolve_recipes(
-    unresolved_recipes: Table<'a, Recipe<'a, Name<'a>>>,
-    assignments: &Table<'a, Assignment<'a>>,
-  ) -> CompilationResult<'a, Table<'a, Rc<Recipe<'a>>>> {
+    unresolved_recipes: Table<'src, Recipe<'src, Name<'src>>>,
+    assignments: &'run Table<'src, Assignment<'src>>,
+  ) -> CompilationResult<'src, Table<'src, Rc<Recipe<'src>>>> {
     let mut resolver = RecipeResolver {
       resolved_recipes: empty(),
       unresolved_recipes,
@@ -48,9 +48,9 @@ impl<'a, 'b> RecipeResolver<'a, 'b> {
 
   fn resolve_variable(
     &self,
-    variable: &Token<'a>,
+    variable: &Token<'src>,
     parameters: &[Parameter],
-  ) -> CompilationResult<'a, ()> {
+  ) -> CompilationResult<'src, ()> {
     let name = variable.lexeme();
     let undefined =
       !self.assignments.contains_key(name) && !parameters.iter().any(|p| p.name.lexeme() == name);
@@ -64,9 +64,9 @@ impl<'a, 'b> RecipeResolver<'a, 'b> {
 
   fn resolve_recipe(
     &mut self,
-    stack: &mut Vec<&'a str>,
-    recipe: Recipe<'a, Name<'a>>,
-  ) -> CompilationResult<'a, Rc<Recipe<'a>>> {
+    stack: &mut Vec<&'src str>,
+    recipe: Recipe<'src, Name<'src>>,
+  ) -> CompilationResult<'src, Rc<Recipe<'src>>> {
     if let Some(resolved) = self.resolved_recipes.get(recipe.name()) {
       return Ok(resolved.clone());
     }
diff --git a/src/runtime_error.rs b/src/runtime_error.rs
index ecc5908..f683ed8 100644
--- a/src/runtime_error.rs
+++ b/src/runtime_error.rs
@@ -1,75 +1,75 @@
 use crate::common::*;
 
 #[derive(Debug)]
-pub(crate) enum RuntimeError<'a> {
+pub(crate) enum RuntimeError<'src> {
   ArgumentCountMismatch {
-    recipe: &'a str,
-    parameters: Vec<&'a Parameter<'a>>,
+    recipe: &'src str,
+    parameters: Vec<&'src Parameter<'src>>,
     found: usize,
     min: usize,
     max: usize,
   },
   Backtick {
-    token: Token<'a>,
+    token: Token<'src>,
     output_error: OutputError,
   },
   Code {
-    recipe: &'a str,
+    recipe: &'src str,
     line_number: Option<usize>,
     code: i32,
   },
   Cygpath {
-    recipe: &'a str,
+    recipe: &'src str,
     output_error: OutputError,
   },
   Dotenv {
     dotenv_error: dotenv::Error,
   },
   FunctionCall {
-    function: Name<'a>,
+    function: Name<'src>,
     message: String,
   },
   Internal {
     message: String,
   },
   IoError {
-    recipe: &'a str,
+    recipe: &'src str,
     io_error: io::Error,
   },
   Shebang {
-    recipe: &'a str,
+    recipe: &'src str,
     command: String,
     argument: Option<String>,
     io_error: io::Error,
   },
   Signal {
-    recipe: &'a str,
+    recipe: &'src str,
     line_number: Option<usize>,
     signal: i32,
   },
   TmpdirIoError {
-    recipe: &'a str,
+    recipe: &'src str,
     io_error: io::Error,
   },
   UnknownOverrides {
-    overrides: Vec<&'a str>,
+    overrides: Vec<&'src str>,
   },
   UnknownRecipes {
-    recipes: Vec<&'a str>,
-    suggestion: Option<&'a str>,
+    recipes: Vec<&'src str>,
+    suggestion: Option<&'src str>,
   },
   Unknown {
-    recipe: &'a str,
+    recipe: &'src str,
     line_number: Option<usize>,
   },
   NoRecipes,
   DefaultRecipeRequiresArguments {
-    recipe: &'a str,
+    recipe: &'src str,
     min_arguments: usize,
   },
 }
 
-impl Error for RuntimeError<'_> {
+impl<'src> Error for RuntimeError<'src> {
   fn code(&self) -> i32 {
     match *self {
       Self::Code { code, .. } => code,
@@ -82,7 +82,7 @@ impl Error for RuntimeError<'_> {
   }
 }
 
-impl<'a> RuntimeError<'a> {
+impl<'src> RuntimeError<'src> {
   fn context(&self) -> Option<Token> {
     use RuntimeError::*;
     match self {
@@ -93,7 +93,7 @@ impl<'a> RuntimeError<'a> {
   }
 }
 
-impl<'a> Display for RuntimeError<'a> {
+impl<'src> Display for RuntimeError<'src> {
   fn fmt(&self, f: &mut Formatter) -> Result<(), fmt::Error> {
     use RuntimeError::*;
 
diff --git a/src/scope.rs b/src/scope.rs
new file mode 100644
index 0000000..155060d
--- /dev/null
+++ b/src/scope.rs
@@ -0,0 +1,57 @@
+use crate::common::*;
+
+#[derive(Debug)]
+pub(crate) struct Scope<'src: 'run, 'run> {
+  parent: Option<&'run Scope<'src, 'run>>,
+  bindings: Table<'src, Binding<'src, String>>,
+}
+
+impl<'src, 'run> Scope<'src, 'run> {
+  pub(crate) fn child(parent: &'run Scope<'src, 'run>) -> Scope<'src, 'run> {
+    Scope {
+      parent: Some(parent),
+      bindings: Table::new(),
+    }
+  }
+
+  pub(crate) fn new() -> Scope<'src, 'run> {
+    Scope {
+      parent: None,
+      bindings: Table::new(),
+    }
+  }
+
+  pub(crate) fn bind(&mut self, export: bool, name: Name<'src>, value: String) {
+    self.bindings.insert(Binding {
+      name,
+      export,
+      value,
+    });
+  }
+
+  pub(crate) fn bound(&self, name: &str) -> bool {
+    self.bindings.contains_key(name)
+  }
+
+  pub(crate) fn value(&self, name: &str) -> Option<&str> {
+    if let Some(binding) = self.bindings.get(name) {
+      Some(binding.value.as_ref())
+    } else if let Some(parent) = self.parent {
+      parent.value(name)
+    } else {
+      None
+    }
+  }
+
+  pub(crate) fn bindings(&self) -> impl Iterator<Item = &Binding<String>> {
+    self.bindings.values()
+  }
+
+  pub(crate) fn names(&self) -> impl Iterator<Item = &str> {
+    self.bindings.keys().cloned()
+  }
+
+  pub(crate) fn parent(&self) -> Option<&'run Scope<'src, 'run>> {
+    self.parent
+  }
+}
diff --git a/src/shebang.rs b/src/shebang.rs
index a5e08e9..907af73 100644
--- a/src/shebang.rs
+++ b/src/shebang.rs
@@ -1,15 +1,15 @@
-pub(crate) struct Shebang<'a> {
-  pub(crate) interpreter: &'a str,
-  pub(crate) argument: Option<&'a str>,
+pub(crate) struct Shebang<'line> {
+  pub(crate) interpreter: &'line str,
+  pub(crate) argument: Option<&'line str>,
 }
 
-impl<'a> Shebang<'a> {
-  pub(crate) fn new(text: &'a str) -> Option<Shebang<'a>> {
-    if !text.starts_with("#!") {
+impl<'line> Shebang<'line> {
+  pub(crate) fn new(line: &'line str) -> Option<Shebang<'line>> {
+    if !line.starts_with("#!") {
       return None;
     }
 
-    let mut pieces = text[2..]
+    let mut pieces = line[2..]
       .lines()
       .nth(0)
       .unwrap_or("")
diff --git a/src/token.rs b/src/token.rs
index 8ca5696..efdf6f4 100644
--- a/src/token.rs
+++ b/src/token.rs
@@ -1,21 +1,21 @@
 use crate::common::*;
 
 #[derive(Debug, PartialEq, Clone, Copy)]
-pub(crate) struct Token<'a> {
+pub(crate) struct Token<'src> {
   pub(crate) offset: usize,
   pub(crate) length: usize,
   pub(crate) line: usize,
   pub(crate) column: usize,
-  pub(crate) src: &'a str,
+  pub(crate) src: &'src str,
   pub(crate) kind: TokenKind,
 }
 
-impl<'a> Token<'a> {
-  pub(crate) fn lexeme(&self) -> &'a str {
+impl<'src> Token<'src> {
+  pub(crate) fn lexeme(&self) -> &'src str {
     &self.src[self.offset..self.offset + self.length]
   }
 
-  pub(crate) fn error(&self, kind: CompilationErrorKind<'a>) -> CompilationError<'a> {
+  pub(crate) fn error(&self, kind: CompilationErrorKind<'src>) -> CompilationError<'src> {
     CompilationError { token: *self, kind }
   }