diff --git a/Cargo.lock b/Cargo.lock
index 3cd24a5c1f..ee75ebfb7a 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -3208,6 +3208,7 @@ dependencies = [
  "roc_problem",
  "roc_region",
  "roc_types",
+ "static_assertions",
  "ven_graph",
 ]
 
diff --git a/compiler/can/Cargo.toml b/compiler/can/Cargo.toml
index 2e8bd639dd..edec9d23ff 100644
--- a/compiler/can/Cargo.toml
+++ b/compiler/can/Cargo.toml
@@ -15,6 +15,7 @@ roc_types = { path = "../types" }
 roc_builtins = { path = "../builtins" }
 ven_graph = { path = "../../vendor/pathfinding" }
 bumpalo = { version = "3.8.0", features = ["collections"] }
+static_assertions = "1.1.0"
 
 [dev-dependencies]
 pretty_assertions = "1.0.0"
diff --git a/compiler/can/src/constraint_soa.rs b/compiler/can/src/constraint_soa.rs
new file mode 100644
index 0000000000..a25c630755
--- /dev/null
+++ b/compiler/can/src/constraint_soa.rs
@@ -0,0 +1,194 @@
+use crate::expected::{Expected, PExpected};
+use roc_collections::all::{MutSet, SendMap};
+use roc_module::symbol::Symbol;
+use roc_region::all::{Located, Region};
+use roc_types::types::{Category, PatternCategory, Type};
+use roc_types::{subs::Variable, types::VariableDetail};
+
+pub struct Constraints {
+    constraints: Vec<Constraint>,
+    types: Vec<Type>,
+    variables: Vec<Variable>,
+    def_types: Vec<(Symbol, Located<Index<Type>>)>,
+    let_constraints: Vec<LetConstraint>,
+    categories: Vec<Category>,
+    pattern_categories: Vec<PatternCategory>,
+    expectations: Vec<Expected<Type>>,
+    pattern_expectations: Vec<PExpected<Type>>,
+}
+
+impl Constraints {
+    pub fn equal_types(
+        &mut self,
+        typ: Type,
+        expected: Expected<Type>,
+        category: Category,
+        region: Region,
+    ) -> Constraint {
+        let type_index = Index::new(self.types.len() as _);
+        let expected_index = Index::new(self.expectations.len() as _);
+        let category_index = Index::new(self.categories.len() as _);
+
+        self.types.push(typ);
+        self.expectations.push(expected);
+        self.categories.push(category);
+
+        Constraint::Eq(type_index, expected_index, category_index, region)
+    }
+
+    pub fn equal_pattern_types(
+        &mut self,
+        typ: Type,
+        expected: PExpected<Type>,
+        category: PatternCategory,
+        region: Region,
+    ) -> Constraint {
+        let type_index = Index::new(self.types.len() as _);
+        let expected_index = Index::new(self.pattern_expectations.len() as _);
+        let category_index = Index::new(self.pattern_categories.len() as _);
+
+        self.types.push(typ);
+        self.pattern_expectations.push(expected);
+        self.pattern_categories.push(category);
+
+        Constraint::Pattern(type_index, expected_index, category_index, region)
+    }
+
+    fn variable_slice<I>(&mut self, it: I) -> Slice<Variable>
+    where
+        I: IntoIterator<Item = Variable>,
+    {
+        let start = self.variables.len();
+        self.variables.extend(it);
+        let length = self.variables.len() - start;
+
+        Slice::new(start as _, length as _)
+    }
+
+    fn def_types_slice<I>(&mut self, it: I) -> Slice<(Symbol, Located<Type>)>
+    where
+        I: IntoIterator<Item = (Symbol, Located<Type>)>,
+    {
+        let start = self.def_types.len();
+
+        for (symbol, loc_type) in it {
+            let type_index = Index::new(self.types.len() as _);
+            let Located { region, value } = loc_type;
+            self.types.push(value);
+
+            self.def_types
+                .push((symbol, Located::at(region, type_index)));
+        }
+
+        let length = self.def_types.len() - start;
+
+        Slice::new(start as _, length as _)
+    }
+
+    pub fn let_contraint<I1, I2, I3>(
+        &mut self,
+        rigid_vars: I1,
+        flex_vars: I2,
+        def_types: I3,
+        defs_constraint: Constraint,
+        ret_constraint: Constraint,
+    ) -> Constraint
+    where
+        I1: IntoIterator<Item = Variable>,
+        I2: IntoIterator<Item = Variable>,
+        I3: IntoIterator<Item = (Symbol, Located<Type>)>,
+    {
+        let defs_and_ret_constraint = Index::new(self.constraints.len() as _);
+
+        self.constraints.push(defs_constraint);
+        self.constraints.push(ret_constraint);
+
+        let let_contraint = LetConstraint {
+            rigid_vars: self.variable_slice(rigid_vars),
+            flex_vars: self.variable_slice(flex_vars),
+            def_types: self.def_types_slice(def_types),
+            defs_and_ret_constraint,
+        };
+
+        let let_index = Index::new(self.let_constraints.len() as _);
+        self.let_constraints.push(let_contraint);
+
+        Constraint::Let(let_index)
+    }
+}
+
+static_assertions::assert_eq_size!([u8; 4 * 8], Constraint);
+static_assertions::assert_eq_size!([u8; 3 * 8 + 4], LetConstraint);
+
+#[derive(Debug, Clone, PartialEq)]
+pub enum Constraint {
+    Eq(Index<Type>, Index<Expected<Type>>, Index<Category>, Region),
+    Store(Index<Type>, Variable, &'static str, u32),
+    Lookup(Symbol, Index<Expected<Type>>, Region),
+    Pattern(
+        Index<Type>,
+        Index<PExpected<Type>>,
+        Index<PatternCategory>,
+        Region,
+    ),
+    True, // Used for things that always unify, e.g. blanks and runtime errors
+    SaveTheEnvironment,
+    Let(Index<LetConstraint>),
+    And(Slice<Constraint>),
+}
+
+#[derive(Debug, Clone, PartialEq)]
+pub struct LetConstraint {
+    pub rigid_vars: Slice<Variable>,
+    pub flex_vars: Slice<Variable>,
+    pub def_types: Slice<(Symbol, Located<Type>)>,
+    pub defs_and_ret_constraint: Index<(Constraint, Constraint)>,
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub struct Index<T> {
+    index: u32,
+    _marker: std::marker::PhantomData<T>,
+}
+
+impl<T> Index<T> {
+    pub const fn new(index: u32) -> Self {
+        Self {
+            index,
+            _marker: std::marker::PhantomData,
+        }
+    }
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub struct Slice<T> {
+    start: u32,
+    length: u16,
+    _marker: std::marker::PhantomData<T>,
+}
+
+impl<T> Slice<T> {
+    pub const fn new(start: u32, length: u16) -> Self {
+        Self {
+            start,
+            length,
+            _marker: std::marker::PhantomData,
+        }
+    }
+
+    pub const fn len(&self) -> usize {
+        self.length as _
+    }
+
+    pub const fn is_empty(&self) -> bool {
+        self.length == 0
+    }
+
+    pub const fn indices(&self) -> std::ops::Range<usize> {
+        self.start as usize..(self.start as usize + self.length as usize)
+    }
+
+    pub fn into_iter(&self) -> impl Iterator<Item = Index<T>> {
+        self.indices().map(|i| Index::new(i as _))
+    }
+}
diff --git a/compiler/can/src/lib.rs b/compiler/can/src/lib.rs
index 7230ab1a36..5cd16be75a 100644
--- a/compiler/can/src/lib.rs
+++ b/compiler/can/src/lib.rs
@@ -4,6 +4,7 @@
 pub mod annotation;
 pub mod builtins;
 pub mod constraint;
+pub mod constraint_soa;
 pub mod def;
 pub mod env;
 pub mod expected;