diff --git a/compiler/can/src/def.rs b/compiler/can/src/def.rs
index 6551655839..c132b89ad3 100644
--- a/compiler/can/src/def.rs
+++ b/compiler/can/src/def.rs
@@ -110,7 +110,7 @@ pub fn canonicalize_defs<'a>(
     mut output: Output,
     var_store: &mut VarStore,
     original_scope: &Scope,
-    loc_defs: &'a bumpalo::collections::Vec<'a, &'a Located<ast::Def<'a>>>,
+    loc_defs: &'a [&'a Located<ast::Def<'a>>],
     pattern_type: PatternType,
 ) -> (CanDefs, Scope, Output, MutMap<Symbol, Region>) {
     // Canonicalizing defs while detecting shadowing involves a multi-step process:
@@ -1239,7 +1239,7 @@ pub fn can_defs_with_return<'a>(
     env: &mut Env<'a>,
     var_store: &mut VarStore,
     scope: Scope,
-    loc_defs: &'a bumpalo::collections::Vec<'a, &'a Located<ast::Def<'a>>>,
+    loc_defs: &'a [&'a Located<ast::Def<'a>>],
     loc_ret: &'a Located<ast::Expr<'a>>,
 ) -> (Expr, Output) {
     let (unsorted, mut scope, defs_output, symbols_introduced) = canonicalize_defs(
diff --git a/compiler/can/src/expr.rs b/compiler/can/src/expr.rs
index 5b8edd794c..314153e612 100644
--- a/compiler/can/src/expr.rs
+++ b/compiler/can/src/expr.rs
@@ -309,7 +309,7 @@ pub fn canonicalize_expr<'a>(
             let mut args = Vec::new();
             let mut outputs = Vec::new();
 
-            for loc_arg in loc_args {
+            for loc_arg in loc_args.iter() {
                 let (arg_expr, arg_out) =
                     canonicalize_expr(env, var_store, scope, loc_arg.region, &loc_arg.value);
 
@@ -562,7 +562,7 @@ pub fn canonicalize_expr<'a>(
 
             let mut can_branches = Vec::with_capacity(branches.len());
 
-            for branch in branches {
+            for branch in branches.iter() {
                 let (can_when_branch, branch_references) =
                     canonicalize_when_branch(env, var_store, scope, region, *branch, &mut output);
 
@@ -788,7 +788,7 @@ fn canonicalize_when_branch<'a>(
     let mut scope = original_scope.clone();
 
     // TODO report symbols not bound in all patterns
-    for loc_pattern in &branch.patterns {
+    for loc_pattern in branch.patterns.iter() {
         let (new_output, can_pattern) = canonicalize_pattern(
             env,
             var_store,
diff --git a/compiler/can/src/module.rs b/compiler/can/src/module.rs
index fa3cfee161..10c6ca38a9 100644
--- a/compiler/can/src/module.rs
+++ b/compiler/can/src/module.rs
@@ -42,7 +42,7 @@ pub struct ModuleOutput {
 #[allow(clippy::too_many_arguments)]
 pub fn canonicalize_module_defs<'a>(
     arena: &Bump,
-    loc_defs: bumpalo::collections::Vec<'a, Located<ast::Def<'a>>>,
+    loc_defs: &'a [Located<ast::Def<'a>>],
     home: ModuleId,
     module_ids: &ModuleIds,
     exposed_ident_ids: IdentIds,
@@ -65,9 +65,9 @@ pub fn canonicalize_module_defs<'a>(
     let mut desugared =
         bumpalo::collections::Vec::with_capacity_in(loc_defs.len() + num_deps, arena);
 
-    for loc_def in loc_defs {
+    for loc_def in loc_defs.iter() {
         desugared.push(&*arena.alloc(Located {
-            value: desugar_def(arena, arena.alloc(loc_def.value)),
+            value: desugar_def(arena, &loc_def.value),
             region: loc_def.region,
         }));
     }
diff --git a/compiler/can/src/operator.rs b/compiler/can/src/operator.rs
index 363674854b..9fae05efe9 100644
--- a/compiler/can/src/operator.rs
+++ b/compiler/can/src/operator.rs
@@ -90,9 +90,10 @@ pub fn desugar_expr<'a>(arena: &'a Bump, loc_expr: &'a Located<Expr<'a>>) -> &'a
         List(elems) | Nested(List(elems)) => {
             let mut new_elems = Vec::with_capacity_in(elems.len(), arena);
 
-            for elem in elems {
+            for elem in elems.iter() {
                 new_elems.push(desugar_expr(arena, elem));
             }
+            let new_elems = new_elems.into_bump_slice();
             let value: Expr<'a> = List(new_elems);
 
             arena.alloc(Located {
@@ -103,7 +104,7 @@ pub fn desugar_expr<'a>(arena: &'a Bump, loc_expr: &'a Located<Expr<'a>>) -> &'a
         Record { fields, update } | Nested(Record { fields, update }) => {
             let mut new_fields = Vec::with_capacity_in(fields.len(), arena);
 
-            for field in fields {
+            for field in fields.iter() {
                 let value = desugar_field(arena, &field.value);
 
                 new_fields.push(Located {
@@ -112,6 +113,8 @@ pub fn desugar_expr<'a>(arena: &'a Bump, loc_expr: &'a Located<Expr<'a>>) -> &'a
                 });
             }
 
+            let new_fields = new_fields.into_bump_slice();
+
             arena.alloc(Located {
                 region: loc_expr.region,
                 value: Record {
@@ -139,6 +142,8 @@ pub fn desugar_expr<'a>(arena: &'a Bump, loc_expr: &'a Located<Expr<'a>>) -> &'a
                 desugared_defs.push(&*arena.alloc(loc_def));
             }
 
+            let desugared_defs = desugared_defs.into_bump_slice();
+
             arena.alloc(Located {
                 value: Defs(desugared_defs, desugar_expr(arena, loc_ret)),
                 region: loc_expr.region,
@@ -147,10 +152,12 @@ pub fn desugar_expr<'a>(arena: &'a Bump, loc_expr: &'a Located<Expr<'a>>) -> &'a
         Apply(loc_fn, loc_args, called_via) | Nested(Apply(loc_fn, loc_args, called_via)) => {
             let mut desugared_args = Vec::with_capacity_in(loc_args.len(), arena);
 
-            for loc_arg in loc_args {
+            for loc_arg in loc_args.iter() {
                 desugared_args.push(desugar_expr(arena, loc_arg));
             }
 
+            let desugared_args = desugared_args.into_bump_slice();
+
             arena.alloc(Located {
                 value: Apply(desugar_expr(arena, loc_fn), desugared_args, *called_via),
                 region: loc_expr.region,
@@ -164,7 +171,7 @@ pub fn desugar_expr<'a>(arena: &'a Bump, loc_expr: &'a Located<Expr<'a>>) -> &'a
                 let desugared = desugar_expr(arena, &branch.value);
 
                 let mut alternatives = Vec::with_capacity_in(branch.patterns.len(), arena);
-                for loc_pattern in &branch.patterns {
+                for loc_pattern in branch.patterns.iter() {
                     alternatives.push(Located {
                         region: loc_pattern.region,
                         value: Pattern::Nested(&loc_pattern.value),
@@ -177,6 +184,8 @@ pub fn desugar_expr<'a>(arena: &'a Bump, loc_expr: &'a Located<Expr<'a>>) -> &'a
                     None
                 };
 
+                let alternatives = alternatives.into_bump_slice();
+
                 desugared_branches.push(&*arena.alloc(WhenBranch {
                     patterns: alternatives,
                     value: Located {
@@ -187,6 +196,8 @@ pub fn desugar_expr<'a>(arena: &'a Bump, loc_expr: &'a Located<Expr<'a>>) -> &'a
                 }));
             }
 
+            let desugared_branches = desugared_branches.into_bump_slice();
+
             arena.alloc(Located {
                 value: When(loc_desugared_cond, desugared_branches),
                 region: loc_expr.region,
@@ -213,6 +224,8 @@ pub fn desugar_expr<'a>(arena: &'a Bump, loc_expr: &'a Located<Expr<'a>>) -> &'a
             let loc_fn_var = arena.alloc(Located { region, value });
             let desugared_args = bumpalo::vec![in arena; desugar_expr(arena, loc_arg)];
 
+            let desugared_args = desugared_args.into_bump_slice();
+
             arena.alloc(Located {
                 value: Apply(loc_fn_var, desugared_args, CalledVia::UnaryOp(op)),
                 region: loc_expr.region,
@@ -463,10 +476,12 @@ fn desugar_bin_op<'a>(arena: &'a Bump, loc_expr: &'a Located<Expr<'_>>) -> &'a L
 
                         args.push(left);
 
-                        for arg in arguments {
+                        for arg in arguments.iter() {
                             args.push(arg);
                         }
 
+                        let args = args.into_bump_slice();
+
                         Apply(function, args, CalledVia::BinOp(Pizza))
                     }
                     expr => {
@@ -480,6 +495,8 @@ fn desugar_bin_op<'a>(arena: &'a Bump, loc_expr: &'a Located<Expr<'_>>) -> &'a L
                             region: right.region,
                         });
 
+                        let args = args.into_bump_slice();
+
                         Apply(function, args, CalledVia::BinOp(Pizza))
                     }
                 }
@@ -498,6 +515,8 @@ fn desugar_bin_op<'a>(arena: &'a Bump, loc_expr: &'a Located<Expr<'_>>) -> &'a L
                     region: loc_op.region,
                 });
 
+                let args = args.into_bump_slice();
+
                 Apply(loc_expr, args, CalledVia::BinOp(binop))
             }
         };
diff --git a/compiler/load/src/docs.rs b/compiler/load/src/docs.rs
index 5284790c8c..cb4e966b93 100644
--- a/compiler/load/src/docs.rs
+++ b/compiler/load/src/docs.rs
@@ -32,7 +32,7 @@ pub struct DocEntry {
 pub fn generate_module_docs<'a>(
     module_name: ModuleName,
     exposed_ident_ids: &'a IdentIds,
-    parsed_defs: &'a bumpalo::collections::Vec<'a, Located<Def<'a>>>,
+    parsed_defs: &'a [Located<Def<'a>>],
 ) -> ModuleDocumentation {
     let (entries, _) =
         parsed_defs
diff --git a/compiler/parse/src/ast.rs b/compiler/parse/src/ast.rs
index 175829452b..3339057ec9 100644
--- a/compiler/parse/src/ast.rs
+++ b/compiler/parse/src/ast.rs
@@ -29,7 +29,7 @@ pub struct InterfaceHeader<'a> {
 
 #[derive(Clone, Debug, PartialEq)]
 pub struct WhenBranch<'a> {
-    pub patterns: Vec<'a, Loc<Pattern<'a>>>,
+    pub patterns: &'a [Loc<Pattern<'a>>],
     pub value: Loc<Expr<'a>>,
     pub guard: Option<Loc<Expr<'a>>>,
 }
@@ -188,10 +188,10 @@ pub enum Expr<'a> {
     AccessorFunction(&'a str),
 
     // Collection Literals
-    List(Vec<'a, &'a Loc<Expr<'a>>>),
+    List(&'a [&'a Loc<Expr<'a>>]),
     Record {
         update: Option<&'a Loc<Expr<'a>>>,
-        fields: Vec<'a, Loc<AssignedField<'a, Expr<'a>>>>,
+        fields: &'a [Loc<AssignedField<'a, Expr<'a>>>],
     },
 
     // Lookups
@@ -205,14 +205,14 @@ pub enum Expr<'a> {
     PrivateTag(&'a str),
 
     // Pattern Matching
-    Closure(&'a Vec<'a, Loc<Pattern<'a>>>, &'a Loc<Expr<'a>>),
+    Closure(&'a [Loc<Pattern<'a>>], &'a Loc<Expr<'a>>),
     /// Multiple defs in a row
-    Defs(Vec<'a, &'a Loc<Def<'a>>>, &'a Loc<Expr<'a>>),
+    Defs(&'a [&'a Loc<Def<'a>>], &'a Loc<Expr<'a>>),
 
     // Application
     /// To apply by name, do Apply(Var(...), ...)
     /// To apply a tag by name, do Apply(Tag(...), ...)
-    Apply(&'a Loc<Expr<'a>>, Vec<'a, &'a Loc<Expr<'a>>>, CalledVia),
+    Apply(&'a Loc<Expr<'a>>, &'a [&'a Loc<Expr<'a>>], CalledVia),
     BinOp(&'a (Loc<Expr<'a>>, Loc<BinOp>, Loc<Expr<'a>>)),
     UnaryOp(&'a Loc<Expr<'a>>, Loc<UnaryOp>),
 
@@ -226,7 +226,7 @@ pub enum Expr<'a> {
         /// Vec, because there may be many patterns, and the guard
         /// is Option<Expr> because each branch may be preceded by
         /// a guard (".. if ..").
-        Vec<'a, &'a WhenBranch<'a>>,
+        &'a [&'a WhenBranch<'a>],
     ),
 
     // Blank Space (e.g. comments, spaces, newlines) before or after an expression.
diff --git a/compiler/parse/src/expr.rs b/compiler/parse/src/expr.rs
index e3baa3d01c..2d67ee3b33 100644
--- a/compiler/parse/src/expr.rs
+++ b/compiler/parse/src/expr.rs
@@ -82,7 +82,7 @@ macro_rules! loc_parenthetical_expr {
                             region: loc_expr_with_extras.region,
                             value: Expr::Apply(
                                 arena.alloc(loc_expr),
-                                allocated_args,
+                                allocated_args.into_bump_slice(),
                                 CalledVia::Space,
                             ),
                         },
@@ -250,7 +250,7 @@ fn expr_to_pattern<'a>(arena: &'a Bump, expr: &Expr<'a>) -> Result<Pattern<'a>,
 
             let mut arg_patterns = Vec::with_capacity_in(loc_args.len(), arena);
 
-            for loc_arg in loc_args {
+            for loc_arg in loc_args.iter() {
                 let region = loc_arg.region;
                 let value = expr_to_pattern(arena, &loc_arg.value)?;
 
@@ -279,7 +279,7 @@ fn expr_to_pattern<'a>(arena: &'a Bump, expr: &Expr<'a>) -> Result<Pattern<'a>,
         } => {
             let mut loc_patterns = Vec::with_capacity_in(fields.len(), arena);
 
-            for loc_assigned_field in fields {
+            for loc_assigned_field in fields.iter() {
                 let region = loc_assigned_field.region;
                 let value = assigned_expr_field_to_pattern(arena, &loc_assigned_field.value)?;
 
@@ -691,7 +691,10 @@ fn parse_def_expr<'a>(
                 // for formatting reasons, we must insert the first def first!
                 defs.insert(0, arena.alloc(loc_first_def));
 
-                Ok((Expr::Defs(defs, arena.alloc(loc_ret)), state))
+                Ok((
+                    Expr::Defs(defs.into_bump_slice(), arena.alloc(loc_ret)),
+                    state,
+                ))
             },
         )
         .parse(arena, state)
@@ -766,6 +769,8 @@ fn parse_def_signature<'a>(
                 // corresponding definition (the one with the body).
                 defs.insert(0, arena.alloc(loc_first_def));
 
+                let defs = defs.into_bump_slice();
+
                 Ok((Expr::Defs(defs, arena.alloc(loc_ret)), state))
             },
         )
@@ -848,7 +853,12 @@ fn closure<'a>(min_indent: u16) -> impl Parser<'a, Expr<'a>> {
         ),
         |arena: &'a Bump, opt_contents| match opt_contents {
             None => Expr::MalformedClosure,
-            Some((params, loc_body)) => Expr::Closure(arena.alloc(params), arena.alloc(loc_body)),
+            Some((params, loc_body)) => {
+                let params: Vec<'a, Located<Pattern<'a>>> = params;
+                let params: &'a [Located<Pattern<'a>>] = params.into_bump_slice();
+
+                Expr::Closure(params, arena.alloc(loc_body))
+            }
         }
     )
 }
@@ -1119,7 +1129,10 @@ mod when {
                 let (branches, state) =
                     attempt!(Attempting::WhenBranch, branches(min_indent)).parse(arena, state)?;
 
-                Ok((Expr::When(arena.alloc(loc_condition), branches), state))
+                Ok((
+                    Expr::When(arena.alloc(loc_condition), branches.into_bump_slice()),
+                    state,
+                ))
             },
         )
     }
@@ -1152,7 +1165,7 @@ mod when {
 
             // Record this as the first branch, then optionally parse additional branches.
             branches.push(arena.alloc(WhenBranch {
-                patterns: loc_first_patterns,
+                patterns: loc_first_patterns.into_bump_slice(),
                 value: loc_first_expr,
                 guard: loc_first_guard,
             }));
@@ -1173,10 +1186,13 @@ mod when {
                     ),
                     branch_result(indented_more)
                 ),
-                |((patterns, guard), expr)| WhenBranch {
-                    patterns,
-                    value: expr,
-                    guard
+                |((patterns, guard), expr)| {
+                    let patterns: Vec<'a, _> = patterns;
+                    WhenBranch {
+                        patterns: patterns.into_bump_slice(),
+                        value: expr,
+                        guard,
+                    }
                 }
             );
 
@@ -1444,7 +1460,11 @@ fn ident_etc<'a>(min_indent: u16) -> impl Parser<'a, Expr<'a>> {
                     }
 
                     Ok((
-                        Expr::Apply(arena.alloc(loc_expr), allocated_args, CalledVia::Space),
+                        Expr::Apply(
+                            arena.alloc(loc_expr),
+                            allocated_args.into_bump_slice(),
+                            CalledVia::Space,
+                        ),
                         state,
                     ))
                 }
@@ -1638,7 +1658,7 @@ pub fn list_literal<'a>(min_indent: u16) -> impl Parser<'a, Expr<'a>> {
                 allocated.push(&*arena.alloc(parsed_elem));
             }
 
-            Expr::List(allocated)
+            Expr::List(allocated.into_bump_slice())
         }),
     )
 }
@@ -1663,7 +1683,7 @@ pub fn record_literal<'a>(min_indent: u16) -> impl Parser<'a, Expr<'a>> {
                     // This is a record literal, not a destructure.
                     let mut value = Expr::Record {
                         update: opt_update.map(|loc_expr| &*arena.alloc(loc_expr)),
-                        fields: loc_assigned_fields.value,
+                        fields: loc_assigned_fields.value.into_bump_slice(),
                     };
 
                     // there can be field access, e.g. `{ x : 4 }.x`