Most Supabase apps ship with RLS policies that look like this:

CREATE POLICY "users_read_own" ON profiles
  FOR SELECT USING (auth.uid() = id);

Looks fine, right? Now answer these:

• What happens when auth.uid() is NULL (anonymous access)?

• Does this policy compose safely with your INSERT policy?

• Can you prove no data leaks exist across all 47 policies in your schema?

You can't. Not with SQL alone.

The Haskell approach

Haskell's type system gives you something SQL never will: compile-time guarantees about your security model.

data Policy (action :: CrudAction) (table :: Symbol) where
  SelectPolicy :: AuthPredicate -> Policy 'Read t
  InsertPolicy :: AuthPredicate -> ValidationCheck -> Policy 'Create t

combineTablePolicies :: Policy 'Read t -> Policy 'Create t -> PolicySet t

When you model policies as typed expressions, entire categories of bugs become impossible:

• NULL-unsafe predicates → caught by Maybe types

• Missing table coverage → caught by exhaustiveness checking

• Conflicting action policies → caught by the GADT structure

From types to SQL

compileToPolicySQL :: Policy action table -> Text
compileToPolicySQL (SelectPolicy pred) = 
  "CREATE POLICY \"auto_select_" <> symbolVal (Proxy @table) 
  <> "\" ON " <> symbolVal (Proxy @table)
  <> " FOR SELECT USING (" <> compilePredicate pred <> ");"

Then property-test the compiled SQL with QuickCheck against thousands of random inputs.

Want to go deeper?

I'm running a weekly mentorship here on Lambda Shield where we build a complete type-safe RLS framework from scratch:

✅ A reusable Haskell DSL for generating Supabase policies

✅ A QuickCheck test suite that catches security holes before deploy

✅ Production migration patterns for real multi-tenant apps

If you're serious about Supabase security, this is the only course that treats it as a type theory problem.

Most Supabase apps ship with RLS policies that look like this:

CREATE POLICY "users_read_own" ON profiles
  FOR SELECT USING (auth.uid() = id);

Looks fine, right? Now answer these questions:

• What happens when auth.uid() is NULL (anonymous access)?

• Does this policy compose safely with your INSERT policy?

• Can you prove no data leaks exist across all 47 policies in your schema?

You can't. Not with SQL alone.

The Haskell approach

Haskell's type system gives you something SQL never will: compile-time guarantees about your security model.

-- This won't compile if your policy has a logical gap
data Policy (action :: CrudAction) (table :: Symbol) where
  SelectPolicy :: AuthPredicate -> Policy 'Read t
  InsertPolicy :: AuthPredicate -> ValidationCheck -> Policy 'Create t

-- Compose policies safely — the type checker enforces consistency
combineTablePolicies :: Policy 'Read t -> Policy 'Create t -> PolicySet t

When you model policies as typed expressions, entire categories of bugs become impossible:

• NULL-unsafe predicates → caught by Maybe types

• Missing table coverage → caught by exhaustiveness checking

• Conflicting action policies → caught by the GADT structure

From types to SQL

The real power is compiling these typed policies down to SQL that Supabase actually executes:

compileToPolicySQL :: Policy action table -> Text
compileToPolicySQL (SelectPolicy pred) = 
  "CREATE POLICY \"auto_select_" <> symbolVal (Proxy @table) 
  <> "\" ON " <> symbolVal (Proxy @table)
  <> " FOR SELECT USING (" <> compilePredicate pred <> ");"

Then you property-test the compiled SQL with QuickCheck to verify it behaves correctly against thousands of random inputs.

Want to go deeper?

I'm running a weekly mentorship program here on Lambda Shield where we build a complete type-safe RLS framework from scratch. You'll walk away with:

✅ A reusable Haskell DSL for generating Supabase policies

✅ A QuickCheck test suite that catches security holes before deploy

✅ Production migration patterns for real multi-tenant apps

If you're serious about Supabase security, this is the only course that treats it as a type theory problem — because that's what it is.

Most Supabase apps ship with RLS policies that look like this:

CREATE POLICY "users_read_own" ON profiles
  FOR SELECT USING (auth.uid() = id);

Looks fine, right? Now answer these questions:

• What happens when auth.uid() is NULL (anonymous access)?

• Does this policy compose safely with your INSERT policy?

• Can you prove no data leaks exist across all 47 policies in your schema?

You can't. Not with SQL alone.

The Haskell approach

Haskell's type system gives you something SQL never will: compile-time guarantees about your security model.

-- This won't compile if your policy has a logical gap
data Policy (action :: CrudAction) (table :: Symbol) where
  SelectPolicy :: AuthPredicate -> Policy 'Read t
  InsertPolicy :: AuthPredicate -> ValidationCheck -> Policy 'Create t

-- Compose policies safely — the type checker enforces consistency
combineTablePolicies :: Policy 'Read t -> Policy 'Create t -> PolicySet t

When you model policies as typed expressions, entire categories of bugs become impossible:

• NULL-unsafe predicates → caught by Maybe types

• Missing table coverage → caught by exhaustiveness checking

• Conflicting action policies → caught by the GADT structure

From types to SQL

The real power is compiling these typed policies down to SQL that Supabase actually executes:

compileToPolicySQL :: Policy action table -> Text
compileToPolicySQL (SelectPolicy pred) = 
  "CREATE POLICY \"auto_select_" <> symbolVal (Proxy @table) 
  <> "\" ON " <> symbolVal (Proxy @table)
  <> " FOR SELECT USING (" <> compilePredicate pred <> ");"

Then you property-test the compiled SQL with QuickCheck to verify it behaves correctly against thousands of random inputs.

Want to go deeper?

I'm running a weekly mentorship program here on Lambda Shield where we build a complete type-safe RLS framework from scratch. You'll walk away with:

✅ A reusable Haskell DSL for generating Supabase policies

✅ A QuickCheck test suite that catches security holes before deploy

✅ Production migration patterns for real multi-tenant apps

If you're serious about Supabase security, this is the only course that treats it as a type theory problem — because that's what it is.