diff --git a/compiler/solve/src/solve.rs b/compiler/solve/src/solve.rs
index 16cc4502c6..56adc9eb27 100644
--- a/compiler/solve/src/solve.rs
+++ b/compiler/solve/src/solve.rs
@@ -16,7 +16,6 @@ use roc_types::types::{
     gather_fields_unsorted_iter, AliasKind, Category, ErrorType, PatternCategory,
 };
 use roc_unify::unify::{unify, Mode, Unified::*};
-use std::collections::hash_map::Entry;
 
 // Type checking system adapted from Elm by Evan Czaplicki, BSD-3-Clause Licensed
 // https://github.com/elm/compiler
@@ -915,6 +914,25 @@ impl RegisterVariable {
             _ => Deferred,
         }
     }
+
+    #[inline(always)]
+    fn with_stack<'a>(
+        subs: &mut Subs,
+        rank: Rank,
+        pools: &mut Pools,
+        arena: &'_ bumpalo::Bump,
+        typ: &'a Type,
+        stack: &mut bumpalo::collections::Vec<'_, TypeToVar<'a>>,
+    ) -> Variable {
+        match Self::from_type(subs, rank, pools, arena, typ) {
+            Self::Direct(var) => var,
+            Self::Deferred => {
+                let var = subs.fresh_unnamed_flex_var();
+                stack.push(TypeToVar::Defer(typ, var));
+                var
+            }
+        }
+    }
 }
 
 #[derive(Debug)]
@@ -1046,7 +1064,8 @@ fn type_to_variable<'a>(
                 // If hit, try to turn the value into an EmptyTagUnion in canonicalization
                 debug_assert!(!tags.is_empty() || !ext.is_empty_tag_union());
 
-                let (union_tags, ext) = type_to_union_tags(subs, rank, pools, arena, tags, ext);
+                let (union_tags, ext) =
+                    type_to_union_tags(subs, rank, pools, arena, tags, ext, &mut stack);
                 let content = Content::Structure(FlatType::TagUnion(union_tags, ext));
 
                 register_with_known_var(subs, destination, rank, pools, content)
@@ -1076,7 +1095,8 @@ fn type_to_variable<'a>(
                 // If hit, try to turn the value into an EmptyTagUnion in canonicalization
                 debug_assert!(!tags.is_empty() || !ext.is_empty_tag_union());
 
-                let (union_tags, ext) = type_to_union_tags(subs, rank, pools, arena, tags, ext);
+                let (union_tags, ext) =
+                    type_to_union_tags(subs, rank, pools, arena, tags, ext, &mut stack);
                 let content =
                     Content::Structure(FlatType::RecursiveTagUnion(*rec_var, union_tags, ext));
 
@@ -1132,7 +1152,7 @@ fn type_to_variable<'a>(
                 };
 
                 let alias_variable = if let Symbol::RESULT_RESULT = *symbol {
-                    roc_result_to_var(subs, rank, pools, arena, actual)
+                    roc_result_to_var(subs, rank, pools, arena, actual, &mut stack)
                 } else {
                     helper!(actual)
                 };
@@ -1212,8 +1232,9 @@ fn roc_result_to_var<'a>(
     subs: &mut Subs,
     rank: Rank,
     pools: &mut Pools,
-    arena: &'a bumpalo::Bump,
-    result_type: &Type,
+    arena: &'_ bumpalo::Bump,
+    result_type: &'a Type,
+    stack: &mut bumpalo::collections::Vec<'_, TypeToVar<'a>>,
 ) -> Variable {
     match result_type {
         Type::TagUnion(tags, ext) => {
@@ -1225,8 +1246,10 @@ fn roc_result_to_var<'a>(
                 debug_assert_eq!(ok, &subs.tag_names[1]);
 
                 if let ([err_type], [ok_type]) = (err_args.as_slice(), ok_args.as_slice()) {
-                    let err_var = type_to_variable(subs, rank, pools, arena, err_type);
-                    let ok_var = type_to_variable(subs, rank, pools, arena, ok_type);
+                    let err_var =
+                        RegisterVariable::with_stack(subs, rank, pools, arena, err_type, stack);
+                    let ok_var =
+                        RegisterVariable::with_stack(subs, rank, pools, arena, ok_type, stack);
 
                     let start = subs.variables.len() as u32;
                     let err_slice = SubsSlice::new(start, 1);
@@ -1317,16 +1340,16 @@ fn sort_and_deduplicate<T>(tag_vars: &mut bumpalo::collections::Vec<(TagName, T)
 fn find_tag_name_run<T>(slice: &[(TagName, T)], subs: &mut Subs) -> Option<SubsSlice<TagName>> {
     use std::cmp::Ordering;
 
-    let tag_name = slice.get(0)?.0.clone();
+    let tag_name = &slice.get(0)?.0;
 
     let mut result = None;
 
     // the `SubsSlice<TagName>` that inserting `slice` into subs would give
     let bigger_slice = SubsSlice::new(subs.tag_names.len() as _, slice.len() as _);
 
-    match subs.tag_name_cache.entry(tag_name) {
-        Entry::Occupied(mut occupied) => {
-            let subs_slice = *occupied.get();
+    match subs.tag_name_cache.get_mut(tag_name) {
+        Some(occupied) => {
+            let subs_slice = *occupied;
 
             let prefix_slice = SubsSlice::new(subs_slice.start, slice.len() as _);
 
@@ -1360,12 +1383,12 @@ fn find_tag_name_run<T>(slice: &[(TagName, T)], subs: &mut Subs) -> Option<SubsS
                 }
                 Ordering::Greater => {
                     // switch to the bigger slice that is not inserted yet, but will be soon
-                    occupied.insert(bigger_slice);
+                    *occupied = bigger_slice;
                 }
             }
         }
-        Entry::Vacant(vacant) => {
-            vacant.insert(bigger_slice);
+        None => {
+            subs.tag_name_cache.push(tag_name, bigger_slice);
         }
     }
 
@@ -1377,8 +1400,9 @@ fn insert_tags_fast_path<'a>(
     subs: &mut Subs,
     rank: Rank,
     pools: &mut Pools,
-    arena: &'a bumpalo::Bump,
-    tags: &[(TagName, Vec<Type>)],
+    arena: &'_ bumpalo::Bump,
+    tags: &'a [(TagName, Vec<Type>)],
+    stack: &mut bumpalo::collections::Vec<'_, TypeToVar<'a>>,
 ) -> UnionTags {
     let new_variable_slices = SubsSlice::reserve_variable_slices(subs, tags.len());
 
@@ -1391,7 +1415,8 @@ fn insert_tags_fast_path<'a>(
                 let new_variables = VariableSubsSlice::reserve_into_subs(subs, arguments.len());
                 let it = (new_variables.indices()).zip(arguments);
                 for (target_index, argument) in it {
-                    let var = type_to_variable(subs, rank, pools, arena, argument);
+                    let var =
+                        RegisterVariable::with_stack(subs, rank, pools, arena, argument, stack);
                     subs.variables[target_index] = var;
                 }
 
@@ -1412,7 +1437,8 @@ fn insert_tags_fast_path<'a>(
                 let new_variables = VariableSubsSlice::reserve_into_subs(subs, arguments.len());
                 let it = (new_variables.indices()).zip(arguments);
                 for (target_index, argument) in it {
-                    let var = type_to_variable(subs, rank, pools, arena, argument);
+                    let var =
+                        RegisterVariable::with_stack(subs, rank, pools, arena, argument, stack);
                     subs.variables[target_index] = var;
                 }
 
@@ -1429,15 +1455,16 @@ fn insert_tags_slow_path<'a>(
     subs: &mut Subs,
     rank: Rank,
     pools: &mut Pools,
-    arena: &'a bumpalo::Bump,
-    tags: &[(TagName, Vec<Type>)],
+    arena: &'_ bumpalo::Bump,
+    tags: &'a [(TagName, Vec<Type>)],
     mut tag_vars: bumpalo::collections::Vec<(TagName, VariableSubsSlice)>,
+    stack: &mut bumpalo::collections::Vec<'_, TypeToVar<'a>>,
 ) -> UnionTags {
     for (tag, tag_argument_types) in tags {
         let new_slice = VariableSubsSlice::reserve_into_subs(subs, tag_argument_types.len());
 
         for (i, arg) in (new_slice.indices()).zip(tag_argument_types) {
-            let var = type_to_variable(subs, rank, pools, arena, arg);
+            let var = RegisterVariable::with_stack(subs, rank, pools, arena, arg, stack);
             subs.variables[i] = var;
         }
 
@@ -1453,39 +1480,39 @@ fn type_to_union_tags<'a>(
     subs: &mut Subs,
     rank: Rank,
     pools: &mut Pools,
-    arena: &'a bumpalo::Bump,
-    tags: &[(TagName, Vec<Type>)],
-    ext: &Type,
+    arena: &'_ bumpalo::Bump,
+    tags: &'a [(TagName, Vec<Type>)],
+    ext: &'a Type,
+    stack: &mut bumpalo::collections::Vec<'_, TypeToVar<'a>>,
 ) -> (UnionTags, Variable) {
     use bumpalo::collections::Vec;
 
     let sorted = tags.len() == 1 || sorted_no_duplicates(tags);
 
     if ext.is_empty_tag_union() {
-        let ext = type_to_variable(subs, rank, pools, arena, &Type::EmptyTagUnion);
-        // let ext = Variable::EMPTY_TAG_UNION;
+        let ext = Variable::EMPTY_TAG_UNION;
 
         let union_tags = if sorted {
-            insert_tags_fast_path(subs, rank, pools, arena, tags)
+            insert_tags_fast_path(subs, rank, pools, arena, tags, stack)
         } else {
             let tag_vars = Vec::with_capacity_in(tags.len(), arena);
-            insert_tags_slow_path(subs, rank, pools, arena, tags, tag_vars)
+            insert_tags_slow_path(subs, rank, pools, arena, tags, tag_vars, stack)
         };
 
         (union_tags, ext)
     } else {
         let mut tag_vars = Vec::with_capacity_in(tags.len(), arena);
 
-        let temp_ext_var = type_to_variable(subs, rank, pools, arena, ext);
+        let temp_ext_var = RegisterVariable::with_stack(subs, rank, pools, arena, ext, stack);
         let (it, ext) =
             roc_types::types::gather_tags_unsorted_iter(subs, UnionTags::default(), temp_ext_var);
 
         tag_vars.extend(it.map(|(n, v)| (n.clone(), v)));
 
         let union_tags = if tag_vars.is_empty() && sorted {
-            insert_tags_fast_path(subs, rank, pools, arena, tags)
+            insert_tags_fast_path(subs, rank, pools, arena, tags, stack)
         } else {
-            insert_tags_slow_path(subs, rank, pools, arena, tags, tag_vars)
+            insert_tags_slow_path(subs, rank, pools, arena, tags, tag_vars, stack)
         };
 
         (union_tags, ext)
diff --git a/compiler/types/src/subs.rs b/compiler/types/src/subs.rs
index 164367a28e..2324d5a8f9 100644
--- a/compiler/types/src/subs.rs
+++ b/compiler/types/src/subs.rs
@@ -1,5 +1,5 @@
 use crate::types::{name_type_var, AliasKind, ErrorType, Problem, RecordField, TypeExt};
-use roc_collections::all::{ImMap, ImSet, MutMap, MutSet, SendMap};
+use roc_collections::all::{ImMap, ImSet, MutSet, SendMap};
 use roc_module::ident::{Lowercase, TagName, Uppercase};
 use roc_module::symbol::Symbol;
 use std::fmt;
@@ -68,7 +68,49 @@ pub struct Subs {
     pub field_names: Vec<Lowercase>,
     pub record_fields: Vec<RecordField<()>>,
     pub variable_slices: Vec<VariableSubsSlice>,
-    pub tag_name_cache: MutMap<TagName, SubsSlice<TagName>>,
+    pub tag_name_cache: TagNameCache,
+}
+
+#[derive(Debug, Clone, Default)]
+pub struct TagNameCache {
+    globals: Vec<Uppercase>,
+    globals_slices: Vec<SubsSlice<TagName>>,
+    /// Currently private tags and closure tags; in the future just closure tags
+    symbols: Vec<Symbol>,
+    symbols_slices: Vec<SubsSlice<TagName>>,
+}
+
+impl TagNameCache {
+    pub fn get_mut(&mut self, tag_name: &TagName) -> Option<&mut SubsSlice<TagName>> {
+        match tag_name {
+            TagName::Global(uppercase) => {
+                // force into block
+                match self.globals.iter().position(|u| u == uppercase) {
+                    Some(index) => Some(&mut self.globals_slices[index]),
+                    None => None,
+                }
+            }
+            TagName::Private(symbol) | TagName::Closure(symbol) => {
+                match self.symbols.iter().position(|s| s == symbol) {
+                    Some(index) => Some(&mut self.symbols_slices[index]),
+                    None => None,
+                }
+            }
+        }
+    }
+
+    pub fn push(&mut self, tag_name: &TagName, slice: SubsSlice<TagName>) {
+        match tag_name {
+            TagName::Global(uppercase) => {
+                self.globals.push(uppercase.clone());
+                self.globals_slices.push(slice);
+            }
+            TagName::Private(symbol) | TagName::Closure(symbol) => {
+                self.symbols.push(*symbol);
+                self.symbols_slices.push(slice);
+            }
+        }
+    }
 }
 
 impl Default for Subs {
@@ -1248,7 +1290,7 @@ impl Subs {
             // store an empty slice at the first position
             // used for "TagOrFunction"
             variable_slices: vec![VariableSubsSlice::default()],
-            tag_name_cache: MutMap::default(),
+            tag_name_cache: TagNameCache::default(),
         };
 
         // NOTE the utable does not (currently) have a with_capacity; using this as the next-best thing
diff --git a/repl_www/public/repl.css b/repl_www/public/repl.css
index f39bccbff6..2c39fc8a3d 100644
--- a/repl_www/public/repl.css
+++ b/repl_www/public/repl.css
@@ -43,16 +43,20 @@ section.history {
   margin: 16px 0;
   padding: 8px;
 }
-#history-text .input {
+.history-item {
+  margin-bottom: 24px;
+}
+.history-item .input {
+  margin: 0;
   margin-bottom: 8px;
 }
-#history-text .output {
-  margin-bottom: 16px;
+.history-item .output {
+  margin: 0;
 }
-#history-text .output-ok {
+.history-item .output-ok {
   color: #0f8;
 }
-#history-text .output-error {
+.history-item .output-error {
   color: #f00;
 }
 .code {
@@ -64,9 +68,7 @@ section.source {
   display: flex;
   flex-direction: column;
 }
-
 section.source textarea {
-  height: 32px;
   padding: 8px;
   margin-bottom: 16px;
 }
diff --git a/repl_www/public/repl.js b/repl_www/public/repl.js
index 008a08c8e7..4ad0323e15 100644
--- a/repl_www/public/repl.js
+++ b/repl_www/public/repl.js
@@ -82,7 +82,9 @@ function onInputKeyup(event) {
       break;
 
     case ENTER:
-      onInputChange({ target: repl.elemSourceInput });
+      if (!event.shiftKey) {
+        onInputChange({ target: repl.elemSourceInput });
+      }
       break;
 
     default:
@@ -168,12 +170,13 @@ function createHistoryEntry(inputText) {
   const historyIndex = repl.inputHistory.length;
   repl.inputHistory.push(inputText);
 
-  const inputElem = document.createElement("div");
-  inputElem.textContent = "> " + inputText;
+  const inputElem = document.createElement("pre");
+  inputElem.textContent = inputText;
   inputElem.classList.add("input");
 
   const historyItem = document.createElement("div");
   historyItem.appendChild(inputElem);
+  historyItem.classList.add("history-item");
 
   repl.elemHistory.appendChild(historyItem);
   repl.elemHistory.scrollTop = repl.elemHistory.scrollHeight;
@@ -182,7 +185,7 @@ function createHistoryEntry(inputText) {
 }
 
 function updateHistoryEntry(index, ok, outputText) {
-  const outputElem = document.createElement("div");
+  const outputElem = document.createElement("pre");
   outputElem.textContent = outputText;
   outputElem.classList.add("output");
   outputElem.classList.add(ok ? "output-ok" : "output-error");
diff --git a/repl_www/public/repl/index.html b/repl_www/public/repl/index.html
index 5bc4ac7e76..4c71ebc6ed 100644
--- a/repl_www/public/repl/index.html
+++ b/repl_www/public/repl/index.html
@@ -1,29 +1,33 @@
 <!DOCTYPE html>
 
 <html>
+  <head>
+    <title>Roc REPL</title>
+    <link rel="stylesheet" href="/repl.css" />
+  </head>
 
-<head>
-  <title>Roc REPL</title>
-  <link rel="stylesheet" href="/repl.css" />
-</head>
+  <body>
+    <div class="body-wrapper">
+      <section class="text">
+        <h1>The rockin' Roc REPL</h1>
+      </section>
 
-<body>
-  <div class="body-wrapper">
-    <section class="text">
-      <h1>The rockin' Roc REPL</h1>
-    </section>
-
-    <section class="history">
-      <div class="scroll-wrap">
-        <div id="history-text" class="scroll code"></div>
-      </div>
-    </section>
-
-    <section class="source">
-      <textarea autofocus id="source-input" class="code" placeholder="Type some Roc code and press Enter"></textarea>
-    </section>
-  </div>
-  <script type="module" src="/repl.js"></script>
-</body>
+      <section class="history">
+        <div class="scroll-wrap">
+          <div id="history-text" class="scroll code"></div>
+        </div>
+      </section>
 
+      <section class="source">
+        <textarea
+          rows="5"
+          autofocus
+          id="source-input"
+          class="code"
+          placeholder="Type some Roc code and press Enter. (Use Shift+Enter for multi-line input)"
+        ></textarea>
+      </section>
+    </div>
+    <script type="module" src="/repl.js"></script>
+  </body>
 </html>
diff --git a/www/build.sh b/www/build.sh
index ae07359997..86db1d0134 100755
--- a/www/build.sh
+++ b/www/build.sh
@@ -12,13 +12,18 @@ rm -rf build/
 cp -r public/ build/
 
 pushd build
+
 # grab the source code and copy it to Netlify's server; if it's not there, fail the build.
 wget https://github.com/rtfeldman/elm-css/files/8037422/roc-source-code.zip
 
 # grab the pre-compiled REPL and copy it to Netlify's server; if it's not there, fail the build.
-wget https://github.com/brian-carroll/mock-repl/files/8167902/roc_repl_wasm.tar.gz
-tar xzvf roc_repl_wasm.tar.gz
-rm roc_repl_wasm.tar.gz
+wget https://github.com/brian-carroll/mock-repl/archive/refs/heads/deploy.zip
+unzip deploy.zip
+mv mock-repl-deploy/* .
+rmdir mock-repl-deploy
+rm deploy.zip
+
+# Copy REPL webpage source files
 cp -r ../../repl_www/public/* .
 
 popd