diff --git a/schala-lang/language/src/lib.rs b/schala-lang/language/src/lib.rs
index e6c17f7..5dbfaa1 100644
--- a/schala-lang/language/src/lib.rs
+++ b/schala-lang/language/src/lib.rs
@@ -21,6 +21,7 @@ use stopwatch::Stopwatch;
 
 use std::cell::RefCell;
 use std::rc::Rc;
+use std::collections::HashSet;
 
 use itertools::Itertools;
 use schala_repl::{ProgrammingLanguageInterface,
@@ -83,7 +84,7 @@ impl Schala {
     let prelude = include_str!("prelude.schala");
     let mut s = Schala::new_blank_env();
 
-    let request = ComputationRequest { source: prelude, debug_requests: vec![] };
+    let request = ComputationRequest { source: prelude, debug_requests: HashSet::default() };
     s.run_computation(request);
     s
   }
@@ -262,39 +263,44 @@ impl ProgrammingLanguageInterface for Schala {
     let stage_names = stage_names();
     self.source_reference.load_new_source(source);
 
-    let token_debug_artifact = None;
-    let parsing_debug_artifact = None;
-    let symbol_debug_artifact = None;
-    let typechecking_debug_artifact = None;
-    let reducing_debug_artifact = None;
-    let eval_debug_artifact = None;
-
     let sw = Stopwatch::start_new();
     let mut stage_durations = Vec::new();
 
     let main_output: Result<String, String> = {
-      let output = tokenizing(source, self, token_debug_artifact);
-      stage_durations.push((stage_names[0].to_string(), sw.elapsed()));
+      let n = 0;
+      let debug_artifact = None;
+      let output = tokenizing(source, self, debug_artifact);
+      stage_durations.push((stage_names[n].to_string(), sw.elapsed()));
       output
     }.and_then(|tokens| {
-      let output = parsing(tokens, self, parsing_debug_artifact);
-      stage_durations.push((stage_names[1].to_string(), sw.elapsed()));
+      let n = 1;
+      let debug_artifact = None;
+      let output = parsing(tokens, self, debug_artifact);
+      stage_durations.push((stage_names[n].to_string(), sw.elapsed()));
       output
     }).and_then(|ast| {
-      let output = symbol_table(ast, self, symbol_debug_artifact);
-      stage_durations.push((stage_names[2].to_string(), sw.elapsed()));
+      let n = 2;
+      let debug_artifact = None;
+      let output = symbol_table(ast, self, debug_artifact);
+      stage_durations.push((stage_names[n].to_string(), sw.elapsed()));
       output
     }).and_then(|ast| {
-      let output = typechecking(ast, self, typechecking_debug_artifact);
-      stage_durations.push((stage_names[3].to_string(), sw.elapsed()));
+      let n = 3;
+      let debug_artifact = None;
+      let output = typechecking(ast, self, debug_artifact);
+      stage_durations.push((stage_names[n].to_string(), sw.elapsed()));
       output
     }).and_then(|ast| {
-      let output = ast_reducing(ast, self, reducing_debug_artifact);
-      stage_durations.push((stage_names[4].to_string(), sw.elapsed()));
+      let n = 4;
+      let debug_artifact = None;
+      let output = ast_reducing(ast, self, debug_artifact);
+      stage_durations.push((stage_names[n].to_string(), sw.elapsed()));
       output
     }).and_then(|reduced_ast| {
-      let output = eval(reduced_ast, self, eval_debug_artifact);
-      stage_durations.push((stage_names[5].to_string(), sw.elapsed()));
+      let n = 5;
+      let debug_artifact = None;
+      let output = eval(reduced_ast, self, debug_artifact);
+      stage_durations.push((stage_names[n].to_string(), sw.elapsed()));
       output
     });
 
diff --git a/schala-repl/src/language.rs b/schala-repl/src/language.rs
index abf8bb6..161b30d 100644
--- a/schala-repl/src/language.rs
+++ b/schala-repl/src/language.rs
@@ -1,4 +1,5 @@
 use std::time;
+use std::collections::HashSet;
 
 pub trait ProgrammingLanguageInterface {
   fn get_language_name(&self) -> String;
@@ -19,7 +20,7 @@ pub trait ProgrammingLanguageInterface {
 
 pub struct ComputationRequest<'a> {
   pub source: &'a str,
-  pub debug_requests: Vec<DebugAsk>,
+  pub debug_requests: HashSet<DebugAsk>,
 }
 
 pub struct ComputationResponse {
diff --git a/schala-repl/src/lib.rs b/schala-repl/src/lib.rs
index f42d4fd..2e02d41 100644
--- a/schala-repl/src/lib.rs
+++ b/schala-repl/src/lib.rs
@@ -12,6 +12,7 @@ extern crate serde_json;
 extern crate includedir;
 extern crate phf;
 
+use std::collections::HashSet;
 use std::path::Path;
 use std::fs::File;
 use std::io::Read;
@@ -68,7 +69,7 @@ fn run_noninteractive(filename: &str, languages: Vec<Box<ProgrammingLanguageInte
 
   let request = ComputationRequest {
     source: &buffer,
-    debug_requests: vec![]
+    debug_requests: HashSet::new(),
   };
 
   let response = language.run_computation(request);
diff --git a/schala-repl/src/repl/mod.rs b/schala-repl/src/repl/mod.rs
index 32e7a26..2523315 100644
--- a/schala-repl/src/repl/mod.rs
+++ b/schala-repl/src/repl/mod.rs
@@ -1,5 +1,6 @@
 use std::fmt::Write as FmtWrite;
 use std::sync::Arc;
+use std::collections::HashSet;
 
 use colored::*;
 use crate::language::{ProgrammingLanguageInterface,
@@ -174,9 +175,9 @@ impl Repl {
   }
 
   fn handle_input(&mut self, input: &str) -> String {
-    let mut debug_requests = vec![];
+    let mut debug_requests = HashSet::new();
     for ask in self.options.debug_asks.iter() {
-      debug_requests.push(ask.clone());
+      debug_requests.insert(ask.clone());
     }
 
     let request = ComputationRequest {