diff --git a/purescript/README.md b/purescript/README.md
index 2064b7a..be5ef05 100644
--- a/purescript/README.md
+++ b/purescript/README.md
@@ -9,6 +9,7 @@
| [ecs](./ecs/) | Purescript-wrapper for [thi.ng/ecs](thi.ng/ecs) |
| [existentials-blog](./existentials-blog) | Perhaps supposed to turn into a blog about existentials? |
| [existentials](./existentials) | Experiment regarding the Church-encoding of existential types |
+| [free](./free/) | Experiments regarding free monads and interpreting algebras |
| [gadts](./gadts) | Experiment regarding ways to encode GADTs in Purescript |
| [lambda-calculus](./lambda-calculus) | Lambda calculus evaluator |
| [lunarline](./lunarline) | Attempt at optimizing a functional language using compile-time partial evaluation |
diff --git a/purescript/free/.gitignore b/purescript/free/.gitignore
new file mode 100644
index 0000000..30efe19
--- /dev/null
+++ b/purescript/free/.gitignore
@@ -0,0 +1,10 @@
+/bower_components/
+/node_modules/
+/.pulp-cache/
+/output/
+/generated-docs/
+/.psc-package/
+/.psc*
+/.purs*
+/.psa*
+/.spago
diff --git a/purescript/free/README.md b/purescript/free/README.md
new file mode 100644
index 0000000..6f6e197
--- /dev/null
+++ b/purescript/free/README.md
@@ -0,0 +1,11 @@
+# Free
+
+My experiments with free monads and interpreting algebras.
+
+## File structure
+
+| File | Description |
+| -------------------------------- | -------------------------------------------------------- |
+| [Exists.purs](./src/Exists.purs) | Basic existential types |
+| [Lambda.purs](./src/Lambda.purs) | Function call algebra and interpreter using existentials |
+| [Math.purs](./src/Math.purs) | Addition & multiplication free monad and interpreter |
diff --git a/purescript/free/packages.dhall b/purescript/free/packages.dhall
new file mode 100644
index 0000000..30f33df
--- /dev/null
+++ b/purescript/free/packages.dhall
@@ -0,0 +1,110 @@
+{-
+Welcome to your new Dhall package-set!
+
+Below are instructions for how to edit this file for most use
+cases, so that you don't need to know Dhall to use it.
+
+## Warning: Don't Move This Top-Level Comment!
+
+Due to how `dhall format` currently works, this comment's
+instructions cannot appear near corresponding sections below
+because `dhall format` will delete the comment. However,
+it will not delete a top-level comment like this one.
+
+## Use Cases
+
+Most will want to do one or both of these options:
+1. Override/Patch a package's dependency
+2. Add a package not already in the default package set
+
+This file will continue to work whether you use one or both options.
+Instructions for each option are explained below.
+
+### Overriding/Patching a package
+
+Purpose:
+- Change a package's dependency to a newer/older release than the
+ default package set's release
+- Use your own modified version of some dependency that may
+ include new API, changed API, removed API by
+ using your custom git repo of the library rather than
+ the package set's repo
+
+Syntax:
+where `entityName` is one of the following:
+- dependencies
+- repo
+- version
+-------------------------------
+let upstream = --
+in upstream
+ with packageName.entityName = "new value"
+-------------------------------
+
+Example:
+-------------------------------
+let upstream = --
+in upstream
+ with halogen.version = "master"
+ with halogen.repo = "https://example.com/path/to/git/repo.git"
+
+ with halogen-vdom.version = "v4.0.0"
+-------------------------------
+
+### Additions
+
+Purpose:
+- Add packages that aren't already included in the default package set
+
+Syntax:
+where `<version>` is:
+- a tag (i.e. "v4.0.0")
+- a branch (i.e. "master")
+- commit hash (i.e. "701f3e44aafb1a6459281714858fadf2c4c2a977")
+-------------------------------
+let upstream = --
+in upstream
+ with new-package-name =
+ { dependencies =
+ [ "dependency1"
+ , "dependency2"
+ ]
+ , repo =
+ "https://example.com/path/to/git/repo.git"
+ , version =
+ "<version>"
+ }
+-------------------------------
+
+Example:
+-------------------------------
+let upstream = --
+in upstream
+ with benchotron =
+ { dependencies =
+ [ "arrays"
+ , "exists"
+ , "profunctor"
+ , "strings"
+ , "quickcheck"
+ , "lcg"
+ , "transformers"
+ , "foldable-traversable"
+ , "exceptions"
+ , "node-fs"
+ , "node-buffer"
+ , "node-readline"
+ , "datetime"
+ , "now"
+ ]
+ , repo =
+ "https://github.com/hdgarrood/purescript-benchotron.git"
+ , version =
+ "v7.0.0"
+ }
+-------------------------------
+-}
+let upstream =
+ https://github.com/purescript/package-sets/releases/download/psc-0.14.0-20210324/packages.dhall sha256:b4564d575da6aed1c042ca7936da97c8b7a29473b63f4515f09bb95fae8dddab
+
+in upstream
diff --git a/purescript/free/spago.dhall b/purescript/free/spago.dhall
new file mode 100644
index 0000000..1715bd6
--- /dev/null
+++ b/purescript/free/spago.dhall
@@ -0,0 +1,19 @@
+{-
+Welcome to a Spago project!
+You can edit this file as you like.
+-}
+{ name = "my-project"
+, dependencies =
+ [ "console"
+ , "debug"
+ , "effect"
+ , "fixed-points"
+ , "free"
+ , "psci-support"
+ , "tuples"
+ , "undefined"
+ , "variant"
+ ]
+, packages = ./packages.dhall
+, sources = [ "src/**/*.purs", "test/**/*.purs" ]
+}
diff --git a/purescript/free/src/Exists.purs b/purescript/free/src/Exists.purs
new file mode 100644
index 0000000..6e0f702
--- /dev/null
+++ b/purescript/free/src/Exists.purs
@@ -0,0 +1,14 @@
+module Existsential where
+
+import Prelude
+
+import Unsafe.Coerce (unsafeCoerce)
+
+foreign import data Test :: forall k. (k -> Type) -> Type
+foreign import data Exists :: forall a b. (a -> b) -> b
+
+mkExists :: forall f a. f a -> Exists f
+mkExists = unsafeCoerce
+
+runExists :: forall f r. (forall a. f a -> r) -> Exists f -> r
+runExists = unsafeCoerce
diff --git a/purescript/free/src/Lambda.purs b/purescript/free/src/Lambda.purs
new file mode 100644
index 0000000..e3289a7
--- /dev/null
+++ b/purescript/free/src/Lambda.purs
@@ -0,0 +1,43 @@
+module Lambda where
+
+import Prelude
+
+import Control.Monad.Free (Free, liftF, resume)
+import Data.Either (Either(..))
+import Existsential (Exists, mkExists, runExists)
+
+data CallData t f = CallData f (f -> t)
+data CallF a t = CallF (Exists (CallData t)) (t -> a)
+
+data LambdaF a
+ = Call (Exists (CallF a))
+
+type Lambda = Free LambdaF
+
+call :: forall a b. (a -> b) -> a -> Lambda b
+call f arg = liftF $ Call (mkExists (CallF callData identity))
+ where
+ callData = mkExists (CallData arg f)
+
+eval :: forall a. Lambda a -> a
+eval = resume >>> case _ of
+ Left (Call ex) -> eval $ run1 ex
+ where
+ run1 :: forall r. Exists (CallF r) -> r
+ run1 = runExists (\(CallF ex' cb) -> cb $ run2 ex')
+
+ run2 :: forall t. Exists (CallData t) -> t
+ run2 = runExists (\(CallData arg f) -> f arg)
+ Right result -> result
+
+test :: Lambda Int
+test = do
+ result <- call ((+) 2) 3
+ pure (result * 3)
+
+instance functorLambdaF :: Functor LambdaF where
+ map f (Call ex) = Call $ flip runExists ex (\(CallF ex' f') -> mkExists (CallF ex' $ f' >>> f))
+
+-- instance showLambda :: Show a => Show (LambdaF a) where
+-- show (Call left right) = show left <> " " <> show right
+-- show (Lambda arg body) = "(\\" <> arg <> " -> " <> show body <> ")"
\ No newline at end of file
diff --git a/purescript/free/src/Main.purs b/purescript/free/src/Main.purs
new file mode 100644
index 0000000..673c66e
--- /dev/null
+++ b/purescript/free/src/Main.purs
@@ -0,0 +1,11 @@
+module Main where
+
+import Prelude
+
+import Effect (Effect)
+import Effect.Class.Console (logShow)
+import Lambda (eval, test)
+
+main :: Effect Unit
+main = do
+ logShow $ eval test
diff --git a/purescript/free/src/Math.purs b/purescript/free/src/Math.purs
new file mode 100644
index 0000000..f957b47
--- /dev/null
+++ b/purescript/free/src/Math.purs
@@ -0,0 +1,34 @@
+module Math where
+
+import Prelude
+
+import Control.Monad.Free (Free, liftF, resume)
+import Data.Either (Either(..))
+
+data MathF a
+ = Add Int Int (Int -> a)
+ | Multiply Int Int (Int -> a)
+
+type Math = Free MathF
+
+---------- Helpers
+eval :: Math Int -> Int
+eval = resume >>> case _ of
+ Right result -> result
+ Left (Add l r cb) -> eval $ cb $ l + r
+ Left (Multiply l r cb) -> eval $ cb $ l * r
+
+seven :: Math Int
+seven = do
+ four <- multiply_ 2 2
+ add_ four 3
+
+---------- Free boilerplate
+add_ :: Int -> Int -> Math Int
+add_ l r = liftF (Add l r identity)
+
+multiply_ :: Int -> Int -> Math Int
+multiply_ l r = liftF (Multiply l r identity)
+
+--------- Typeclass instances
+derive instance functorMath :: Functor MathF
\ No newline at end of file
diff --git a/purescript/free/test/Main.purs b/purescript/free/test/Main.purs
new file mode 100644
index 0000000..f91f98c
--- /dev/null
+++ b/purescript/free/test/Main.purs
@@ -0,0 +1,11 @@
+module Test.Main where
+
+import Prelude
+
+import Effect (Effect)
+import Effect.Class.Console (log)
+
+main :: Effect Unit
+main = do
+ log "🍝"
+ log "You should add some tests."