diff --git a/crates/compiler/gen_wasm/src/backend.rs b/crates/compiler/gen_wasm/src/backend.rs
index ce374c31e1..4c734b5ec1 100644
--- a/crates/compiler/gen_wasm/src/backend.rs
+++ b/crates/compiler/gen_wasm/src/backend.rs
@@ -36,7 +36,8 @@ pub enum ProcSource {
     Roc,
     Helper,
     /// Wrapper function for higher-order calls from Zig to Roc
-    HigherOrderWrapper(usize),
+    HigherOrderMapper(usize),
+    HigherOrderCompare(usize),
 }
 
 #[derive(Debug)]
@@ -463,7 +464,7 @@ impl<'a> WasmBackend<'a> {
         self.module.names.append_function(wasm_fn_index, name);
     }
 
-    /// Build a wrapper around a Roc procedure so that it can be called from our higher-order Zig builtins.
+    /// Build a wrapper around a Roc procedure so that it can be called from Zig builtins List.map*
     ///
     /// The generic Zig code passes *pointers* to all of the argument values (e.g. on the heap in a List).
     /// Numbers up to 64 bits are passed by value, so we need to load them from the provided pointer.
@@ -471,7 +472,7 @@ impl<'a> WasmBackend<'a> {
     ///
     /// NOTE: If the builtins expected the return pointer first and closure data last, we could eliminate the wrapper
     /// when all args are pass-by-reference and non-zero size. But currently we need it to swap those around.
-    pub fn build_higher_order_wrapper(
+    pub fn build_higher_order_mapper(
         &mut self,
         wrapper_lookup_idx: usize,
         inner_lookup_idx: usize,
@@ -515,44 +516,22 @@ impl<'a> WasmBackend<'a> {
         for (i, wrapper_arg) in wrapper_arg_layouts.iter().enumerate() {
             let is_closure_data = i == 0; // Skip closure data (first for wrapper, last for inner)
             let is_return_pointer = i == wrapper_arg_layouts.len() - 1; // Skip return pointer (may not be an arg for inner. And if it is, swaps from end to start)
-            if is_closure_data || is_return_pointer || wrapper_arg.stack_size(TARGET_INFO) == 0 {
+            if is_closure_data || is_return_pointer {
                 continue;
             }
-            n_inner_wasm_args += 1;
 
-            // Load wrapper argument. They're all pointers.
-            self.code_builder.get_local(LocalId(i as u32));
-
-            // Dereference any primitive-valued arguments
-            match wrapper_arg {
-                Layout::Boxed(inner_arg) => match inner_arg {
-                    Layout::Builtin(Builtin::Int(IntWidth::U8 | IntWidth::I8)) => {
-                        self.code_builder.i32_load8_u(Bytes1, 0);
-                    }
-                    Layout::Builtin(Builtin::Int(IntWidth::U16 | IntWidth::I16)) => {
-                        self.code_builder.i32_load16_u(Bytes2, 0);
-                    }
-                    Layout::Builtin(Builtin::Int(IntWidth::U32 | IntWidth::I32)) => {
-                        self.code_builder.i32_load(Bytes4, 0);
-                    }
-                    Layout::Builtin(Builtin::Int(IntWidth::U64 | IntWidth::I64)) => {
-                        self.code_builder.i64_load(Bytes8, 0);
-                    }
-                    Layout::Builtin(Builtin::Float(FloatWidth::F32)) => {
-                        self.code_builder.f32_load(Bytes4, 0);
-                    }
-                    Layout::Builtin(Builtin::Float(FloatWidth::F64)) => {
-                        self.code_builder.f64_load(Bytes8, 0);
-                    }
-                    Layout::Builtin(Builtin::Bool) => {
-                        self.code_builder.i32_load8_u(Bytes1, 0);
-                    }
-                    _ => {
-                        // Any other layout is a pointer, which we've already loaded. Nothing to do!
-                    }
-                },
-                x => internal_error!("Higher-order wrapper: expected a Box layout, got {:?}", x),
+            let inner_layout = match wrapper_arg {
+                Layout::Boxed(inner) => inner,
+                x => internal_error!("Expected a Boxed layout, got {:?}", x),
+            };
+            if inner_layout.stack_size(TARGET_INFO) == 0 {
+                continue;
             }
+
+            // Load the argument pointer. If it's a primitive value, dereference it too.
+            n_inner_wasm_args += 1;
+            self.code_builder.get_local(LocalId(i as u32));
+            self.dereference_boxed_value(inner_layout);
         }
 
         // If the inner function has closure data, it's the last arg of the inner fn
@@ -594,6 +573,90 @@ impl<'a> WasmBackend<'a> {
         self.reset();
     }
 
+    /// Build a wrapper around a Roc comparison proc so that it can be called from higher-order Zig builtins.
+    /// Comparison procedure signature is: closure_data, a, b -> Order (u8)
+    ///
+    /// The generic Zig code passes *pointers* to all of the argument values (e.g. on the heap in a List).
+    /// Numbers up to 64 bits are passed by value, so we need to load them from the provided pointer.
+    /// Everything else is passed by reference, so we can just pass the pointer through.
+    pub fn build_higher_order_compare(
+        &mut self,
+        wrapper_lookup_idx: usize,
+        inner_lookup_idx: usize,
+    ) {
+        use ValueType::*;
+
+        let ProcLookupData {
+            name: wrapper_name,
+            layout: wrapper_proc_layout,
+            ..
+        } = self.proc_lookup[wrapper_lookup_idx];
+        let closure_data_layout = wrapper_proc_layout.arguments[0];
+        let value_layout = wrapper_proc_layout.arguments[1];
+
+        let mut n_inner_args = 2;
+        if closure_data_layout.stack_size(TARGET_INFO) > 0 {
+            self.code_builder.get_local(LocalId(0));
+            n_inner_args += 1;
+        }
+
+        let inner_layout = match value_layout {
+            Layout::Boxed(inner) => inner,
+            x => internal_error!("Expected a Boxed layout, got {:?}", x),
+        };
+        self.code_builder.get_local(LocalId(1));
+        self.dereference_boxed_value(inner_layout);
+        self.code_builder.get_local(LocalId(2));
+        self.dereference_boxed_value(inner_layout);
+
+        // Call the wrapped inner function
+        let inner_wasm_fn_index = self.fn_index_offset + inner_lookup_idx as u32;
+        self.code_builder
+            .call(inner_wasm_fn_index, n_inner_args, true);
+
+        // Write empty function header (local variables array with zero length)
+        self.code_builder.build_fn_header_and_footer(&[], 0, None);
+
+        self.module.add_function_signature(Signature {
+            param_types: bumpalo::vec![in self.env.arena; I32; 3],
+            ret_type: Some(ValueType::I32),
+        });
+
+        self.append_proc_debug_name(wrapper_name);
+        self.reset();
+    }
+
+    fn dereference_boxed_value(&mut self, inner: &Layout) {
+        use Align::*;
+
+        match inner {
+            Layout::Builtin(Builtin::Int(IntWidth::U8 | IntWidth::I8)) => {
+                self.code_builder.i32_load8_u(Bytes1, 0);
+            }
+            Layout::Builtin(Builtin::Int(IntWidth::U16 | IntWidth::I16)) => {
+                self.code_builder.i32_load16_u(Bytes2, 0);
+            }
+            Layout::Builtin(Builtin::Int(IntWidth::U32 | IntWidth::I32)) => {
+                self.code_builder.i32_load(Bytes4, 0);
+            }
+            Layout::Builtin(Builtin::Int(IntWidth::U64 | IntWidth::I64)) => {
+                self.code_builder.i64_load(Bytes8, 0);
+            }
+            Layout::Builtin(Builtin::Float(FloatWidth::F32)) => {
+                self.code_builder.f32_load(Bytes4, 0);
+            }
+            Layout::Builtin(Builtin::Float(FloatWidth::F64)) => {
+                self.code_builder.f64_load(Bytes8, 0);
+            }
+            Layout::Builtin(Builtin::Bool) => {
+                self.code_builder.i32_load8_u(Bytes1, 0);
+            }
+            _ => {
+                // Any other layout is a pointer, which we've already loaded. Nothing to do!
+            }
+        }
+    }
+
     /**********************************************************
 
             STATEMENTS
diff --git a/crates/compiler/gen_wasm/src/lib.rs b/crates/compiler/gen_wasm/src/lib.rs
index 1d00e29f64..7b580f8ce0 100644
--- a/crates/compiler/gen_wasm/src/lib.rs
+++ b/crates/compiler/gen_wasm/src/lib.rs
@@ -13,7 +13,6 @@ use bumpalo::collections::Vec;
 use bumpalo::{self, Bump};
 
 use roc_collections::all::{MutMap, MutSet};
-use roc_module::low_level::LowLevelWrapperType;
 use roc_module::symbol::{Interns, ModuleId, Symbol};
 use roc_mono::code_gen_help::CodeGenHelp;
 use roc_mono::ir::{Proc, ProcLayout};
@@ -96,17 +95,10 @@ pub fn build_app_module<'a>(
         host_module.import.function_count() as u32 + host_module.code.preloaded_count;
 
     // Pre-pass over the procedure names & layouts
-    // Filter out procs we're going to inline & gather some data for lookups
-    let mut fn_index: u32 = fn_index_offset;
-    for ((sym, proc_layout), proc) in procedures.into_iter() {
-        if matches!(
-            LowLevelWrapperType::from_symbol(sym),
-            LowLevelWrapperType::CanBeReplacedBy(_)
-        ) {
-            continue;
-        }
+    // Create a lookup to tell us the final index of each proc in the output file
+    for (i, ((sym, proc_layout), proc)) in procedures.into_iter().enumerate() {
+        let fn_index = fn_index_offset + i as u32;
         procs.push(proc);
-
         if env.exposed_to_host.contains(&sym) {
             maybe_main_fn_index = Some(fn_index);
 
@@ -124,8 +116,6 @@ pub fn build_app_module<'a>(
             layout: proc_layout,
             source: ProcSource::Roc,
         });
-
-        fn_index += 1;
     }
 
     let mut backend = WasmBackend::new(
@@ -179,7 +169,8 @@ pub fn build_app_module<'a>(
         match source {
             Roc => { /* already generated */ }
             Helper => backend.build_proc(helper_iter.next().unwrap()),
-            HigherOrderWrapper(inner_idx) => backend.build_higher_order_wrapper(idx, *inner_idx),
+            HigherOrderMapper(inner_idx) => backend.build_higher_order_mapper(idx, *inner_idx),
+            HigherOrderCompare(inner_idx) => backend.build_higher_order_compare(idx, *inner_idx),
         }
     }
 
diff --git a/crates/compiler/gen_wasm/src/low_level.rs b/crates/compiler/gen_wasm/src/low_level.rs
index d8bd80c81f..f0038316ac 100644
--- a/crates/compiler/gen_wasm/src/low_level.rs
+++ b/crates/compiler/gen_wasm/src/low_level.rs
@@ -530,7 +530,45 @@ impl<'a> LowLevelCall<'a> {
 
                 backend.call_host_fn_after_loading_args(bitcode::LIST_APPEND, 7, false);
             }
-            ListPrepend => todo!("{:?}", self.lowlevel),
+            ListPrepend => {
+                // List.prepend : List elem, elem -> List elem
+
+                let list: Symbol = self.arguments[0];
+                let elem: Symbol = self.arguments[1];
+
+                let elem_layout = unwrap_list_elem_layout(self.ret_layout);
+                let (elem_width, elem_align) = elem_layout.stack_size_and_alignment(TARGET_INFO);
+                let (elem_local, elem_offset, _) =
+                    ensure_symbol_is_in_memory(backend, elem, *elem_layout, backend.env.arena);
+
+                // Zig arguments              Wasm types
+                //  (return pointer)           i32
+                //  list: RocList              i64, i32
+                //  alignment: u32             i32
+                //  element: Opaque            i32
+                //  element_width: usize       i32
+
+                // return pointer and list
+                backend.storage.load_symbols_for_call(
+                    backend.env.arena,
+                    &mut backend.code_builder,
+                    &[list],
+                    self.ret_symbol,
+                    &WasmLayout::new(&self.ret_layout),
+                    CallConv::Zig,
+                );
+
+                backend.code_builder.i32_const(elem_align as i32);
+
+                backend.code_builder.get_local(elem_local);
+                if elem_offset > 0 {
+                    backend.code_builder.i32_const(elem_offset as i32);
+                    backend.code_builder.i32_add();
+                }
+                backend.code_builder.i32_const(elem_width as i32);
+
+                backend.call_host_fn_after_loading_args(bitcode::LIST_PREPEND, 6, false);
+            }
             ListSublist => {
                 // As a low-level, record is destructured
                 //  List.sublist : List elem, start : Nat, len : Nat -> List elem
@@ -1980,7 +2018,7 @@ pub fn call_higher_order_lowlevel<'a>(
 
     // We create a wrapper around the passed function, which just unboxes the arguments.
     // This allows Zig builtins to have a generic pointer-based interface.
-    let source = {
+    let helper_proc_source = {
         let passed_proc_layout = ProcLayout {
             arguments: argument_layouts,
             result: *result_layout,
@@ -1993,7 +2031,13 @@ pub fn call_higher_order_lowlevel<'a>(
                 *name == fn_name.name() && layout == &passed_proc_layout
             })
             .unwrap();
-        ProcSource::HigherOrderWrapper(passed_proc_index)
+        match op {
+            ListSortWith { .. } => ProcSource::HigherOrderCompare(passed_proc_index),
+            ListMap { .. } | ListMap2 { .. } | ListMap3 { .. } | ListMap4 { .. } => {
+                ProcSource::HigherOrderMapper(passed_proc_index)
+            }
+            DictWalk { .. } => todo!("DictWalk"),
+        }
     };
     let wrapper_sym = backend.create_symbol(&format!("#wrap#{:?}", fn_name));
     let wrapper_layout = {
@@ -2013,16 +2057,30 @@ pub fn call_higher_order_lowlevel<'a>(
                 .take(n_non_closure_args)
                 .map(Layout::Boxed),
         );
-        wrapper_arg_layouts.push(Layout::Boxed(result_layout));
 
-        ProcLayout {
-            arguments: wrapper_arg_layouts.into_bump_slice(),
-            result: Layout::UNIT,
-            captures_niche: fn_name.captures_niche(),
+        match helper_proc_source {
+            ProcSource::HigherOrderMapper(_) => {
+                // Our convention for mappers is that they write to the heap via the last argument
+                wrapper_arg_layouts.push(Layout::Boxed(result_layout));
+                ProcLayout {
+                    arguments: wrapper_arg_layouts.into_bump_slice(),
+                    result: Layout::UNIT,
+                    captures_niche: fn_name.captures_niche(),
+                }
+            }
+            ProcSource::HigherOrderCompare(_) => ProcLayout {
+                arguments: wrapper_arg_layouts.into_bump_slice(),
+                result: *result_layout,
+                captures_niche: fn_name.captures_niche(),
+            },
+            ProcSource::Roc | ProcSource::Helper => {
+                internal_error!("Should never reach here for {:?}", helper_proc_source)
+            }
         }
     };
 
-    let wrapper_fn_idx = backend.register_helper_proc(wrapper_sym, wrapper_layout, source);
+    let wrapper_fn_idx =
+        backend.register_helper_proc(wrapper_sym, wrapper_layout, helper_proc_source);
     let wrapper_fn_ptr = backend.get_fn_ptr(wrapper_fn_idx);
     let inc_fn_ptr = match closure_data_layout {
         Layout::Struct {
@@ -2094,7 +2152,40 @@ pub fn call_higher_order_lowlevel<'a>(
             *owns_captured_environment,
         ),
 
-        ListSortWith { .. } | DictWalk { .. } => todo!("{:?}", op),
+        ListSortWith { xs } => {
+            let elem_layout = unwrap_list_elem_layout(backend.storage.symbol_layouts[xs]);
+            let (element_width, alignment) = elem_layout.stack_size_and_alignment(TARGET_INFO);
+
+            let cb = &mut backend.code_builder;
+
+            // (return pointer)      i32
+            // input: RocList,       i64, i32
+            // caller: CompareFn,    i32
+            // data: Opaque,         i32
+            // inc_n_data: IncN,     i32
+            // data_is_owned: bool,  i32
+            // alignment: u32,       i32
+            // element_width: usize, i32
+
+            backend.storage.load_symbols(cb, &[return_sym]);
+            backend.storage.load_symbol_zig(cb, *xs);
+            cb.i32_const(wrapper_fn_ptr);
+            if closure_data_exists {
+                backend.storage.load_symbols(cb, &[*captured_environment]);
+            } else {
+                // load_symbols assumes that a zero-size arg should be eliminated in code gen,
+                // but that's a specialization that our Zig code doesn't have! Pass a null pointer.
+                cb.i32_const(0);
+            }
+            cb.i32_const(inc_fn_ptr);
+            cb.i32_const(*owns_captured_environment as i32);
+            cb.i32_const(alignment as i32);
+            cb.i32_const(element_width as i32);
+
+            backend.call_host_fn_after_loading_args(bitcode::LIST_SORT_WITH, 9, false);
+        }
+
+        DictWalk { .. } => todo!("{:?}", op),
     }
 }
 
diff --git a/crates/compiler/gen_wasm/src/storage.rs b/crates/compiler/gen_wasm/src/storage.rs
index 0c7b03d5da..5f11037d29 100644
--- a/crates/compiler/gen_wasm/src/storage.rs
+++ b/crates/compiler/gen_wasm/src/storage.rs
@@ -222,6 +222,7 @@ impl<'a> Storage<'a> {
         arena: &'a Bump,
     ) {
         let mut wide_number_args = Vec::with_capacity_in(args.len(), arena);
+        let mut has_zero_size_arg = false;
 
         for (layout, symbol) in args {
             self.symbol_layouts.insert(*symbol, *layout);
@@ -260,6 +261,7 @@ impl<'a> Storage<'a> {
                             if size == 0 {
                                 // An argument with zero size is purely conceptual, and will not exist in Wasm.
                                 // However we need to track the symbol, so we treat it like a local variable.
+                                has_zero_size_arg = true;
                                 StackMemoryLocation::FrameOffset(0)
                             } else {
                                 StackMemoryLocation::PointerArg(LocalId(local_index))
@@ -282,7 +284,7 @@ impl<'a> Storage<'a> {
         // If any arguments are 128-bit numbers, store them in the stack frame
         // This makes it easier to keep track of which symbols are on the Wasm value stack
         // The frame pointer will be the next local after the arguments
-        if self.stack_frame_size > 0 {
+        if self.stack_frame_size > 0 || has_zero_size_arg {
             let frame_ptr = LocalId(self.arg_types.len() as u32);
             self.stack_frame_pointer = Some(frame_ptr);
             self.local_types.push(PTR_TYPE);
diff --git a/crates/compiler/gen_wasm/src/wasm32_result.rs b/crates/compiler/gen_wasm/src/wasm32_result.rs
index 9c5ae09f77..43db6ff086 100644
--- a/crates/compiler/gen_wasm/src/wasm32_result.rs
+++ b/crates/compiler/gen_wasm/src/wasm32_result.rs
@@ -14,7 +14,7 @@ use crate::wasm_module::{
     linking::SymInfo, linking::WasmObjectSymbol, Align, CodeBuilder, Export, ExportType, LocalId,
     Signature, ValueType, WasmModule,
 };
-use roc_std::{RocDec, RocList, RocOrder, RocStr};
+use roc_std::{RocDec, RocList, RocOrder, RocResult, RocStr};
 
 /// Type-driven wrapper generation
 pub trait Wasm32Result {
@@ -200,6 +200,17 @@ impl<T: Wasm32Result> Wasm32Result for RocList<T> {
     }
 }
 
+impl<T: Wasm32Sized, E: Wasm32Sized> Wasm32Result for RocResult<T, E> {
+    fn build_wrapper_body(code_builder: &mut CodeBuilder, main_function_index: u32) {
+        build_wrapper_body_stack_memory(
+            code_builder,
+            main_function_index,
+            Ord::max(T::ACTUAL_WIDTH, E::ACTUAL_WIDTH)
+                + Ord::max(T::ALIGN_OF_WASM, E::ALIGN_OF_WASM),
+        )
+    }
+}
+
 impl<T: Wasm32Result> Wasm32Result for &'_ T {
     build_wrapper_body_primitive!(i32_store, Align::Bytes4);
 }
diff --git a/crates/compiler/gen_wasm/src/wasm32_sized.rs b/crates/compiler/gen_wasm/src/wasm32_sized.rs
index 3ba889c022..a127474c66 100644
--- a/crates/compiler/gen_wasm/src/wasm32_sized.rs
+++ b/crates/compiler/gen_wasm/src/wasm32_sized.rs
@@ -1,4 +1,4 @@
-use roc_std::{RocDec, RocList, RocOrder, RocStr};
+use roc_std::{RocDec, RocList, RocOrder, RocResult, RocStr};
 
 pub trait Wasm32Sized: Sized {
     const SIZE_OF_WASM: usize;
@@ -41,6 +41,11 @@ impl<T: Wasm32Sized> Wasm32Sized for RocList<T> {
     const ALIGN_OF_WASM: usize = 4;
 }
 
+impl<T: Wasm32Sized, E: Wasm32Sized> Wasm32Sized for RocResult<T, E> {
+    const ALIGN_OF_WASM: usize = max2(T::ALIGN_OF_WASM, E::ALIGN_OF_WASM);
+    const SIZE_OF_WASM: usize = max2(T::ACTUAL_WIDTH, E::ACTUAL_WIDTH) + 1;
+}
+
 impl<T: Wasm32Sized> Wasm32Sized for &'_ T {
     const SIZE_OF_WASM: usize = 4;
     const ALIGN_OF_WASM: usize = 4;
diff --git a/crates/compiler/test_gen/src/gen_abilities.rs b/crates/compiler/test_gen/src/gen_abilities.rs
index 065501e3f9..b207f42561 100644
--- a/crates/compiler/test_gen/src/gen_abilities.rs
+++ b/crates/compiler/test_gen/src/gen_abilities.rs
@@ -10,9 +10,9 @@ use crate::helpers::wasm::assert_evals_to;
 #[cfg(test)]
 use indoc::indoc;
 
-#[cfg(all(test, feature = "gen-llvm"))]
+#[cfg(all(test, any(feature = "gen-llvm", feature = "gen-wasm")))]
 use roc_std::RocList;
-#[cfg(all(test, feature = "gen-llvm"))]
+#[cfg(all(test, any(feature = "gen-llvm", feature = "gen-wasm")))]
 use roc_std::RocStr;
 
 #[test]
@@ -223,7 +223,7 @@ fn ability_used_as_type_still_compiles() {
 }
 
 #[test]
-#[cfg(any(feature = "gen-llvm"))]
+#[cfg(any(feature = "gen-llvm", feature = "gen-wasm"))]
 fn encode() {
     assert_evals_to!(
         indoc!(
@@ -269,7 +269,7 @@ fn encode() {
 }
 
 #[test]
-#[cfg(any(feature = "gen-llvm"))]
+#[cfg(any(feature = "gen-llvm", feature = "gen-wasm"))]
 fn decode() {
     assert_evals_to!(
         indoc!(
@@ -327,7 +327,7 @@ fn decode() {
 }
 
 #[test]
-#[cfg(any(feature = "gen-llvm"))]
+#[cfg(any(feature = "gen-llvm", feature = "gen-wasm"))]
 fn encode_use_stdlib() {
     assert_evals_to!(
         indoc!(
diff --git a/crates/compiler/test_gen/src/gen_list.rs b/crates/compiler/test_gen/src/gen_list.rs
index 2c674b64ed..e5268772a1 100644
--- a/crates/compiler/test_gen/src/gen_list.rs
+++ b/crates/compiler/test_gen/src/gen_list.rs
@@ -307,8 +307,9 @@ fn list_split() {
         (RocList<i64>, RocList<i64>,)
     );
 }
+
 #[test]
-#[cfg(any(feature = "gen-llvm"))]
+#[cfg(any(feature = "gen-llvm", feature = "gen-wasm"))]
 fn list_drop() {
     assert_evals_to!(
         "List.drop [1,2,3] 2",
@@ -353,7 +354,7 @@ fn list_drop_at() {
 }
 
 #[test]
-#[cfg(any(feature = "gen-llvm"))]
+#[cfg(any(feature = "gen-llvm", feature = "gen-wasm"))]
 fn list_intersperse() {
     assert_evals_to!(
         indoc!(
@@ -398,7 +399,7 @@ fn list_drop_at_shared() {
 }
 
 #[test]
-#[cfg(any(feature = "gen-llvm"))]
+#[cfg(any(feature = "gen-llvm", feature = "gen-wasm"))]
 fn list_drop_if_empty_list_of_int() {
     assert_evals_to!(
         indoc!(
@@ -415,7 +416,7 @@ fn list_drop_if_empty_list_of_int() {
 }
 
 #[test]
-#[cfg(any(feature = "gen-llvm"))]
+#[cfg(any(feature = "gen-llvm", feature = "gen-wasm"))]
 fn list_drop_if_empty_list() {
     assert_evals_to!(
         indoc!(
@@ -432,7 +433,7 @@ fn list_drop_if_empty_list() {
 }
 
 #[test]
-#[cfg(any(feature = "gen-llvm"))]
+#[cfg(any(feature = "gen-llvm", feature = "gen-wasm"))]
 fn list_drop_if_always_false_for_non_empty_list() {
     assert_evals_to!(
         indoc!(
@@ -446,7 +447,7 @@ fn list_drop_if_always_false_for_non_empty_list() {
 }
 
 #[test]
-#[cfg(any(feature = "gen-llvm"))]
+#[cfg(any(feature = "gen-llvm", feature = "gen-wasm"))]
 fn list_drop_if_always_true_for_non_empty_list() {
     assert_evals_to!(
         indoc!(
@@ -460,7 +461,7 @@ fn list_drop_if_always_true_for_non_empty_list() {
 }
 
 #[test]
-#[cfg(any(feature = "gen-llvm"))]
+#[cfg(any(feature = "gen-llvm", feature = "gen-wasm"))]
 fn list_drop_if_geq3() {
     assert_evals_to!(
         indoc!(
@@ -474,7 +475,7 @@ fn list_drop_if_geq3() {
 }
 
 #[test]
-#[cfg(any(feature = "gen-llvm"))]
+#[cfg(any(feature = "gen-llvm", feature = "gen-wasm"))]
 fn list_drop_if_string_eq() {
     assert_evals_to!(
         indoc!(
@@ -488,7 +489,7 @@ fn list_drop_if_string_eq() {
 }
 
 #[test]
-#[cfg(any(feature = "gen-llvm"))]
+#[cfg(any(feature = "gen-llvm", feature = "gen-wasm"))]
 fn list_drop_last() {
     assert_evals_to!(
         "List.dropLast [1, 2, 3]",
@@ -508,7 +509,7 @@ fn list_drop_last() {
 }
 
 #[test]
-#[cfg(any(feature = "gen-llvm"))]
+#[cfg(any(feature = "gen-llvm", feature = "gen-wasm"))]
 fn list_drop_last_mutable() {
     assert_evals_to!(
         indoc!(
@@ -530,7 +531,7 @@ fn list_drop_last_mutable() {
 }
 
 #[test]
-#[cfg(any(feature = "gen-llvm"))]
+#[cfg(any(feature = "gen-llvm", feature = "gen-wasm"))]
 fn list_drop_first() {
     assert_evals_to!(
         "List.dropFirst [1, 2, 3]",
@@ -630,7 +631,7 @@ fn list_append_longer_list() {
 }
 
 #[test]
-#[cfg(any(feature = "gen-llvm"))]
+#[cfg(any(feature = "gen-llvm", feature = "gen-wasm"))]
 fn list_prepend() {
     assert_evals_to!("List.prepend [] 1", RocList::from_slice(&[1]), RocList<i64>);
     assert_evals_to!(
@@ -669,7 +670,7 @@ fn list_prepend() {
 }
 
 #[test]
-#[cfg(any(feature = "gen-llvm"))]
+#[cfg(any(feature = "gen-llvm", feature = "gen-wasm"))]
 fn list_prepend_bools() {
     assert_evals_to!(
         "List.prepend [True, False] True",
@@ -679,7 +680,7 @@ fn list_prepend_bools() {
 }
 
 #[test]
-#[cfg(any(feature = "gen-llvm"))]
+#[cfg(any(feature = "gen-llvm", feature = "gen-wasm"))]
 fn list_prepend_big_list() {
     assert_evals_to!(
         "List.prepend [10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 100, 100, 100, 100] 9",
@@ -795,7 +796,7 @@ fn list_walk_until_sum() {
 }
 
 #[test]
-#[cfg(any(feature = "gen-llvm"))]
+#[cfg(any(feature = "gen-llvm", feature = "gen-wasm"))]
 fn list_walk_implements_position() {
     assert_evals_to!(
         r#"
@@ -818,7 +819,7 @@ fn list_walk_implements_position() {
             Some v -> v
         "#,
         2,
-        i64
+        usize
     );
 }
 
@@ -841,7 +842,7 @@ fn list_walk_until_even_prefix_sum() {
 }
 
 #[test]
-#[cfg(any(feature = "gen-llvm"))]
+#[cfg(any(feature = "gen-llvm", feature = "gen-wasm"))]
 fn list_keep_if_empty_list_of_int() {
     assert_evals_to!(
         indoc!(
@@ -859,7 +860,7 @@ fn list_keep_if_empty_list_of_int() {
 }
 
 #[test]
-#[cfg(any(feature = "gen-llvm"))]
+#[cfg(any(feature = "gen-llvm", feature = "gen-wasm"))]
 fn list_keep_if_empty_list() {
     assert_evals_to!(
         indoc!(
@@ -878,7 +879,7 @@ fn list_keep_if_empty_list() {
 }
 
 #[test]
-#[cfg(any(feature = "gen-llvm"))]
+#[cfg(any(feature = "gen-llvm", feature = "gen-wasm"))]
 fn list_keep_if_always_true_for_non_empty_list() {
     assert_evals_to!(
         indoc!(
@@ -900,7 +901,7 @@ fn list_keep_if_always_true_for_non_empty_list() {
 }
 
 #[test]
-#[cfg(any(feature = "gen-llvm"))]
+#[cfg(any(feature = "gen-llvm", feature = "gen-wasm"))]
 fn list_keep_if_always_false_for_non_empty_list() {
     assert_evals_to!(
         indoc!(
@@ -918,7 +919,7 @@ fn list_keep_if_always_false_for_non_empty_list() {
 }
 
 #[test]
-#[cfg(any(feature = "gen-llvm"))]
+#[cfg(any(feature = "gen-llvm", feature = "gen-wasm"))]
 fn list_keep_if_one() {
     assert_evals_to!(
         indoc!(
@@ -936,7 +937,7 @@ fn list_keep_if_one() {
 }
 
 #[test]
-#[cfg(any(feature = "gen-llvm"))]
+#[cfg(any(feature = "gen-llvm", feature = "gen-wasm"))]
 fn list_keep_if_str_is_hello() {
     assert_evals_to!(
         indoc!(
@@ -2289,7 +2290,7 @@ fn quicksort_singleton() {
 }
 
 #[test]
-#[cfg(any(feature = "gen-llvm"))]
+#[cfg(any(feature = "gen-llvm", feature = "gen-wasm"))]
 fn empty_list_increment_decrement() {
     assert_evals_to!(
         indoc!(
@@ -2301,12 +2302,12 @@ fn empty_list_increment_decrement() {
             "#
         ),
         0,
-        i64
+        usize
     );
 }
 
 #[test]
-#[cfg(any(feature = "gen-llvm"))]
+#[cfg(any(feature = "gen-llvm", feature = "gen-wasm"))]
 fn list_literal_increment_decrement() {
     assert_evals_to!(
         indoc!(
@@ -2318,7 +2319,7 @@ fn list_literal_increment_decrement() {
             "#
         ),
         6,
-        i64
+        usize
     );
 }
 
@@ -2496,7 +2497,7 @@ fn list_product() {
 }
 
 #[test]
-#[cfg(any(feature = "gen-llvm"))]
+#[cfg(any(feature = "gen-llvm", feature = "gen-wasm"))]
 fn list_keep_void() {
     assert_evals_to!(
         "List.keepOks [] (\\x -> x)",
@@ -2512,7 +2513,7 @@ fn list_keep_void() {
 }
 
 #[test]
-#[cfg(any(feature = "gen-llvm"))]
+#[cfg(any(feature = "gen-llvm", feature = "gen-wasm"))]
 fn list_keep_oks() {
     assert_evals_to!(
         "List.keepOks [Ok {}, Ok {}] (\\x -> x)",
@@ -2537,7 +2538,7 @@ fn list_keep_oks() {
 }
 
 #[test]
-#[cfg(any(feature = "gen-llvm"))]
+#[cfg(any(feature = "gen-llvm", feature = "gen-wasm"))]
 fn list_keep_errs() {
     assert_evals_to!(
         "List.keepErrs [Err {}, Err {}] (\\x -> x)",
@@ -2613,7 +2614,7 @@ fn list_range() {
 }
 
 #[test]
-#[cfg(any(feature = "gen-llvm"))]
+#[cfg(any(feature = "gen-llvm", feature = "gen-wasm"))]
 fn list_sort_with() {
     assert_evals_to!(
         "List.sortWith [] Num.compare",
@@ -2633,7 +2634,7 @@ fn list_sort_with() {
 }
 
 #[test]
-#[cfg(any(feature = "gen-llvm"))]
+#[cfg(any(feature = "gen-llvm", feature = "gen-wasm"))]
 fn list_sort_asc() {
     assert_evals_to!(
         "List.sortAsc []",
@@ -2648,7 +2649,7 @@ fn list_sort_asc() {
 }
 
 #[test]
-#[cfg(any(feature = "gen-llvm"))]
+#[cfg(any(feature = "gen-llvm", feature = "gen-wasm"))]
 fn list_sort_desc() {
     assert_evals_to!(
         "List.sortDesc []",
@@ -2712,7 +2713,7 @@ fn list_all_empty_with_unknown_element_type() {
 }
 
 #[test]
-#[cfg(any(feature = "gen-llvm"))]
+#[cfg(any(feature = "gen-llvm", feature = "gen-wasm"))]
 #[should_panic(expected = r#"Roc failed with message: "invalid ret_layout""#)]
 fn lists_with_incompatible_type_param_in_if() {
     assert_evals_to!(
@@ -2733,7 +2734,7 @@ fn lists_with_incompatible_type_param_in_if() {
 }
 
 #[test]
-#[cfg(any(feature = "gen-llvm"))]
+#[cfg(any(feature = "gen-llvm", feature = "gen-wasm"))]
 fn map_with_index_multi_record() {
     // see https://github.com/rtfeldman/roc/issues/1700
     assert_evals_to!(
@@ -2777,7 +2778,7 @@ fn empty_list_of_function_type() {
 }
 
 #[test]
-#[cfg(any(feature = "gen-llvm"))]
+#[cfg(any(feature = "gen-llvm", feature = "gen-wasm"))]
 fn list_join_map() {
     assert_evals_to!(
         indoc!(
@@ -2797,7 +2798,7 @@ fn list_join_map() {
 }
 
 #[test]
-#[cfg(any(feature = "gen-llvm"))]
+#[cfg(any(feature = "gen-llvm", feature = "gen-wasm"))]
 fn list_join_map_empty() {
     assert_evals_to!(
         indoc!(
@@ -2874,7 +2875,7 @@ fn list_find_empty_layout() {
 }
 
 #[test]
-#[cfg(any(feature = "gen-llvm"))]
+#[cfg(any(feature = "gen-llvm", feature = "gen-wasm"))]
 fn list_find_index() {
     assert_evals_to!(
         indoc!(
@@ -2885,12 +2886,12 @@ fn list_find_index() {
             "#
         ),
         1,
-        i64
+        usize
     );
 }
 
 #[test]
-#[cfg(any(feature = "gen-llvm"))]
+#[cfg(any(feature = "gen-llvm", feature = "gen-wasm"))]
 fn list_find_index_not_found() {
     assert_evals_to!(
         indoc!(
@@ -2901,12 +2902,12 @@ fn list_find_index_not_found() {
             "#
         ),
         999,
-        i64
+        usize
     );
 }
 
 #[test]
-#[cfg(any(feature = "gen-llvm"))]
+#[cfg(any(feature = "gen-llvm", feature = "gen-wasm"))]
 fn list_find_index_empty_typed_list() {
     assert_evals_to!(
         indoc!(
@@ -2917,12 +2918,12 @@ fn list_find_index_empty_typed_list() {
             "#
         ),
         999,
-        i64
+        usize
     );
 }
 
 #[test]
-#[cfg(any(feature = "gen-llvm"))]
+#[cfg(any(feature = "gen-llvm", feature = "gen-wasm"))]
 fn monomorphized_lists() {
     assert_evals_to!(
         indoc!(
@@ -2936,7 +2937,7 @@ fn monomorphized_lists() {
             "#
         ),
         18,
-        u64
+        usize
     )
 }
 
@@ -2960,7 +2961,7 @@ fn with_capacity() {
 }
 
 #[test]
-#[cfg(any(feature = "gen-llvm"))]
+#[cfg(any(feature = "gen-llvm", feature = "gen-wasm"))]
 fn call_function_in_empty_list() {
     assert_evals_to!(
         indoc!(
diff --git a/crates/compiler/test_gen/src/gen_primitives.rs b/crates/compiler/test_gen/src/gen_primitives.rs
index f02f5b5c6e..bebed9b687 100644
--- a/crates/compiler/test_gen/src/gen_primitives.rs
+++ b/crates/compiler/test_gen/src/gen_primitives.rs
@@ -981,7 +981,7 @@ fn overflow_frees_list() {
 }
 
 #[test]
-#[cfg(any(feature = "gen-llvm"))]
+#[cfg(any(feature = "gen-llvm", feature = "gen-wasm"))]
 #[should_panic(expected = "Roc failed with message: ")]
 fn undefined_variable() {
     assert_evals_to!(
@@ -999,7 +999,7 @@ fn undefined_variable() {
 }
 
 #[test]
-#[cfg(any(feature = "gen-llvm"))]
+#[cfg(any(feature = "gen-llvm", feature = "gen-wasm"))]
 #[should_panic(expected = "Roc failed with message: ")]
 fn annotation_without_body() {
     assert_evals_to!(
@@ -1039,7 +1039,7 @@ fn simple_closure() {
 }
 
 #[test]
-#[cfg(any(feature = "gen-llvm"))]
+#[cfg(any(feature = "gen-llvm", feature = "gen-wasm"))]
 fn nested_closure() {
     assert_evals_to!(
         indoc!(
@@ -1121,7 +1121,7 @@ fn specialize_closure() {
 }
 
 #[test]
-#[cfg(any(feature = "gen-llvm"))]
+#[cfg(any(feature = "gen-llvm", feature = "gen-wasm"))]
 fn io_poc_effect() {
     assert_non_opt_evals_to!(
         indoc!(
@@ -1152,7 +1152,7 @@ fn io_poc_effect() {
 }
 
 #[test]
-#[cfg(any(feature = "gen-llvm"))]
+#[cfg(any(feature = "gen-llvm", feature = "gen-wasm"))]
 fn io_poc_desugared() {
     assert_evals_to!(
         indoc!(
@@ -1374,7 +1374,7 @@ fn linked_list_singleton() {
 }
 
 #[test]
-#[cfg(any(feature = "gen-llvm"))]
+#[cfg(any(feature = "gen-llvm", feature = "gen-wasm"))]
 fn recursive_function_with_rigid() {
     assert_non_opt_evals_to!(
         indoc!(
@@ -1401,7 +1401,7 @@ fn recursive_function_with_rigid() {
 }
 
 #[test]
-#[cfg(any(feature = "gen-llvm"))]
+#[cfg(any(feature = "gen-llvm", feature = "gen-wasm"))]
 fn rbtree_insert() {
     assert_non_opt_evals_to!(
         indoc!(
@@ -2020,7 +2020,7 @@ fn hof_conditional() {
 }
 
 #[test]
-#[cfg(any(feature = "gen-llvm"))]
+#[cfg(any(feature = "gen-llvm", feature = "gen-wasm"))]
 #[should_panic(
     expected = "Roc failed with message: \"Shadowing { original_region: @55-56, shadow: @88-89 Ident"
 )]
@@ -2497,7 +2497,7 @@ fn backpassing_result() {
 }
 
 #[test]
-#[cfg(any(feature = "gen-llvm"))]
+#[cfg(any(feature = "gen-llvm", feature = "gen-wasm"))]
 #[should_panic(expected = "Shadowing { original_region: @55-56, shadow: @72-73 Ident")]
 fn function_malformed_pattern() {
     assert_evals_to!(
@@ -2589,7 +2589,7 @@ fn module_thunk_is_function() {
 }
 
 #[test]
-#[cfg(any(feature = "gen-llvm"))]
+#[cfg(any(feature = "gen-llvm", feature = "gen-wasm"))]
 #[should_panic(expected = "Roc failed with message: ")]
 fn hit_unresolved_type_variable() {
     assert_evals_to!(
@@ -2732,7 +2732,7 @@ fn lambda_set_byte() {
 }
 
 #[test]
-#[cfg(any(feature = "gen-llvm"))]
+#[cfg(any(feature = "gen-llvm", feature = "gen-wasm"))]
 fn lambda_set_struct_byte() {
     assert_evals_to!(
         indoc!(
@@ -2791,7 +2791,7 @@ fn lambda_set_enum_byte_byte() {
 }
 
 #[test]
-#[cfg(any(feature = "gen-llvm"))]
+#[cfg(any(feature = "gen-llvm", feature = "gen-wasm"))]
 fn list_walk_until() {
     // see https://github.com/rtfeldman/roc/issues/1576
     assert_evals_to!(
@@ -2872,7 +2872,7 @@ fn int_literal_not_specialized_no_annotation() {
 }
 
 #[test]
-#[cfg(any(feature = "gen-llvm"))]
+#[cfg(any(feature = "gen-llvm", feature = "gen-wasm"))]
 fn unresolved_tvar_when_capture_is_unused() {
     // see https://github.com/rtfeldman/roc/issues/1585
     assert_evals_to!(
@@ -2899,7 +2899,7 @@ fn unresolved_tvar_when_capture_is_unused() {
 }
 
 #[test]
-#[cfg(any(feature = "gen-llvm"))]
+#[cfg(any(feature = "gen-llvm", feature = "gen-wasm"))]
 #[should_panic(expected = "Roc failed with message: ")]
 fn value_not_exposed_hits_panic() {
     assert_evals_to!(
@@ -2969,7 +2969,7 @@ fn mix_function_and_closure_level_of_indirection() {
 }
 
 #[test]
-#[cfg(any(feature = "gen-llvm"))]
+#[cfg(any(feature = "gen-llvm", feature = "gen-wasm"))]
 #[cfg_attr(debug_assertions, ignore)] // this test stack-overflows the compiler in debug mode
 fn do_pass_bool_byte_closure_layout() {
     // see https://github.com/rtfeldman/roc/pull/1706
@@ -3172,7 +3172,7 @@ fn alias_defined_out_of_order() {
 }
 
 #[test]
-#[cfg(any(feature = "gen-llvm"))]
+#[cfg(any(feature = "gen-llvm", feature = "gen-wasm"))]
 fn recursively_build_effect() {
     assert_evals_to!(
         indoc!(
@@ -3243,7 +3243,7 @@ fn polymophic_expression_captured_inside_closure() {
 }
 
 #[test]
-#[cfg(any(feature = "gen-llvm"))]
+#[cfg(any(feature = "gen-llvm", feature = "gen-wasm"))]
 fn issue_2322() {
     assert_evals_to!(
         indoc!(
@@ -3481,7 +3481,7 @@ fn mutual_recursion_top_level_defs() {
 }
 
 #[test]
-#[cfg(any(feature = "gen-llvm"))]
+#[cfg(any(feature = "gen-llvm", feature = "gen-wasm"))]
 fn polymorphic_lambda_captures_polymorphic_value() {
     assert_evals_to!(
         indoc!(
@@ -3500,7 +3500,7 @@ fn polymorphic_lambda_captures_polymorphic_value() {
 }
 
 #[test]
-#[cfg(any(feature = "gen-llvm"))]
+#[cfg(any(feature = "gen-llvm", feature = "gen-wasm"))]
 fn lambda_capture_niche_u64_vs_u8_capture() {
     assert_evals_to!(
         indoc!(
@@ -3527,7 +3527,7 @@ fn lambda_capture_niche_u64_vs_u8_capture() {
 }
 
 #[test]
-#[cfg(any(feature = "gen-llvm"))]
+#[cfg(any(feature = "gen-llvm", feature = "gen-wasm"))]
 fn lambda_capture_niches_with_other_lambda_capture() {
     assert_evals_to!(
         indoc!(
@@ -3560,7 +3560,7 @@ fn lambda_capture_niches_with_other_lambda_capture() {
 }
 
 #[test]
-#[cfg(any(feature = "gen-llvm"))]
+#[cfg(any(feature = "gen-llvm", feature = "gen-wasm"))]
 fn lambda_capture_niches_with_non_capturing_function() {
     assert_evals_to!(
         indoc!(
@@ -3593,7 +3593,7 @@ fn lambda_capture_niches_with_non_capturing_function() {
 }
 
 #[test]
-#[cfg(any(feature = "gen-llvm"))]
+#[cfg(any(feature = "gen-llvm", feature = "gen-wasm"))]
 fn lambda_capture_niches_have_captured_function_in_closure() {
     assert_evals_to!(
         indoc!(
diff --git a/crates/compiler/test_gen/src/gen_result.rs b/crates/compiler/test_gen/src/gen_result.rs
index fb757fd7b3..7c524083e1 100644
--- a/crates/compiler/test_gen/src/gen_result.rs
+++ b/crates/compiler/test_gen/src/gen_result.rs
@@ -224,7 +224,7 @@ fn is_err() {
 }
 
 #[test]
-#[cfg(any(feature = "gen-llvm"))]
+#[cfg(any(feature = "gen-llvm", feature = "gen-wasm"))]
 fn roc_result_ok() {
     assert_evals_to!(
         indoc!(
@@ -241,7 +241,7 @@ fn roc_result_ok() {
 }
 
 #[test]
-#[cfg(any(feature = "gen-llvm"))]
+#[cfg(any(feature = "gen-llvm", feature = "gen-wasm"))]
 fn roc_result_err() {
     assert_evals_to!(
         indoc!(
@@ -258,7 +258,7 @@ fn roc_result_err() {
 }
 
 #[test]
-#[cfg(any(feature = "gen-llvm"))]
+#[cfg(any(feature = "gen-llvm", feature = "gen-wasm"))]
 fn issue_2583_specialize_errors_behind_unified_branches() {
     assert_evals_to!(
         r#"
diff --git a/crates/compiler/test_gen/src/gen_tags.rs b/crates/compiler/test_gen/src/gen_tags.rs
index a2de31653d..50ade390da 100644
--- a/crates/compiler/test_gen/src/gen_tags.rs
+++ b/crates/compiler/test_gen/src/gen_tags.rs
@@ -1182,7 +1182,7 @@ fn applied_tag_function() {
 }
 
 #[test]
-#[cfg(any(feature = "gen-llvm"))]
+#[cfg(any(feature = "gen-llvm", feature = "gen-wasm"))]
 fn applied_tag_function_result() {
     assert_evals_to!(
         indoc!(
@@ -1221,7 +1221,7 @@ fn applied_tag_function_linked_list() {
 }
 
 #[test]
-#[cfg(any(feature = "gen-llvm"))]
+#[cfg(any(feature = "gen-llvm", feature = "gen-wasm"))]
 fn applied_tag_function_pair() {
     assert_evals_to!(
         indoc!(
@@ -1260,7 +1260,7 @@ fn tag_must_be_its_own_type() {
 }
 
 #[test]
-#[cfg(any(feature = "gen-llvm"))]
+#[cfg(any(feature = "gen-llvm", feature = "gen-wasm"))]
 fn recursive_tag_union_into_flat_tag_union() {
     // Comprehensive test for correctness in cli/tests/repl_eval
     assert_evals_to!(
@@ -1535,7 +1535,7 @@ fn issue_2458_deep_recursion_var() {
 }
 
 #[test]
-#[cfg(any(feature = "gen-llvm"))]
+#[cfg(any(feature = "gen-llvm", feature = "gen-wasm"))]
 fn issue_1162() {
     assert_evals_to!(
         indoc!(
@@ -1705,7 +1705,7 @@ fn issue_2900_unreachable_pattern() {
 }
 
 #[test]
-#[cfg(any(feature = "gen-llvm"))]
+#[cfg(any(feature = "gen-llvm", feature = "gen-wasm"))]
 fn issue_3261_non_nullable_unwrapped_recursive_union_at_index() {
     assert_evals_to!(
         indoc!(
diff --git a/crates/compiler/test_gen/src/helpers/from_wasmer_memory.rs b/crates/compiler/test_gen/src/helpers/from_wasmer_memory.rs
index d8e149959f..bf37cd9de6 100644
--- a/crates/compiler/test_gen/src/helpers/from_wasmer_memory.rs
+++ b/crates/compiler/test_gen/src/helpers/from_wasmer_memory.rs
@@ -1,5 +1,5 @@
 use roc_gen_wasm::wasm32_sized::Wasm32Sized;
-use roc_std::{RocDec, RocList, RocOrder, RocStr};
+use roc_std::{RocDec, RocList, RocOrder, RocResult, RocStr};
 use std::convert::TryInto;
 
 pub trait FromWasmerMemory: Wasm32Sized {
@@ -95,6 +95,22 @@ impl<T: FromWasmerMemory + Clone> FromWasmerMemory for RocList<T> {
     }
 }
 
+impl<T: FromWasmerMemory + Wasm32Sized, E: FromWasmerMemory + Wasm32Sized> FromWasmerMemory
+    for RocResult<T, E>
+{
+    fn decode(memory: &wasmer::Memory, offset: u32) -> Self {
+        let tag_offset = Ord::max(T::ACTUAL_WIDTH, E::ACTUAL_WIDTH);
+        let tag = <u8 as FromWasmerMemory>::decode(memory, offset + tag_offset as u32);
+        if tag == 1 {
+            let value = <T as FromWasmerMemory>::decode(memory, offset);
+            RocResult::ok(value)
+        } else {
+            let payload = <E as FromWasmerMemory>::decode(memory, offset);
+            RocResult::err(payload)
+        }
+    }
+}
+
 impl<T: FromWasmerMemory> FromWasmerMemory for &'_ T {
     fn decode(memory: &wasmer::Memory, offset: u32) -> Self {
         let elements = <u32 as FromWasmerMemory>::decode(memory, offset);
diff --git a/crates/compiler/test_gen/src/helpers/wasm.rs b/crates/compiler/test_gen/src/helpers/wasm.rs
index fad15bc621..de0e863397 100644
--- a/crates/compiler/test_gen/src/helpers/wasm.rs
+++ b/crates/compiler/test_gen/src/helpers/wasm.rs
@@ -364,7 +364,7 @@ macro_rules! assert_evals_to {
     };
 
     ($src:expr, $expected:expr, $ty:ty, $transform:expr) => {
-        $crate::helpers::wasm::assert_evals_to!($src, $expected, $ty, $transform, false);
+        $crate::helpers::wasm::assert_evals_to!($src, $expected, $ty, $transform, false)
     };
 
     ($src:expr, $expected:expr, $ty:ty, $transform:expr, $ignore_problems: expr) => {{