4 files changed, 96 insertions, 3 deletions
diff --git a/examples/impure-concept.lisp b/examples/impure-concept.lisp
index e612339..f769424 100644
--- a/examples/impure-concept.lisp
+++ b/examples/impure-concept.lisp
@@ -3,7 +3,7 @@
 ; Pure functions can only call pure functions.
 ; Impure function names end in an exclamation mark (!) by convention.
 ; The top-level context is impure but has special rules
-;   related to (import!) and (let!).
+;   related to `import!`, `let!`, and other builtins.
 
 ; pure function
 (let! f (\[x] x))
diff --git a/examples/records-concept.lisp b/examples/records-concept.lisp
new file mode 100644
index 0000000..420fa9f
--- /dev/null
+++ b/examples/records-concept.lisp
@@ -0,0 +1,51 @@
+; Records are named tuples with an identifier. `record!` is a builtin function
+; that generates functions for creating, reading and modifying a record.
+; In type system terms, records are intersections.
+
+; `record!` can only be called in the top-level context.
+
+(record! Ns/User
+    name
+    phone-number)
+
+; Generates the following functions:
+
+(let! user
+    (Ns/User/create "John" "010-123-456"))
+    ; user ~> (Ns/User name:"John" phone-number:"010-123-456")
+
+(Ns/User/get-name user) ; => "John"
+(Ns/User/get-phone-number user) ; => "010-123-456"
+
+(Ns/User/set-name "Rick" user)
+    ; => (Ns/User name:"Rick" phone-number:"010-123-456")
+(Ns/User/set-phone-number unit user)
+    ; => (Ns/User name:"Rick" phone-number:<unit>)
+
+
+
+
+; Unions are unions of records with an identifier. `union!` is a builtin function
+; that generates functions for manipulating the records in the union.
+
+; `union!` can only be called in the top-level context.
+
+(union! Ns/Maybe
+    (just value)
+    (nothing))
+
+; Generates the following functions:
+
+(let! m1 (Ns/Maybe/just 10)) ; m1 ~> (Ns/Maybe/Just value:10)
+(let! m2 (Ns/Maybe/nothing)) ; m2 ~> (Ns/Maybe/Nothing)
+
+(Ns/Maybe/Just/get-value m1) ; => 10
+
+
+
+
+; The builtin function `kind` returns the identifier as a string for any record value
+
+(kind m1) ; => "Ns/Maybe/Just"
+(kind m2) ; => "Ns/Maybe/Nothing"
+(kind user) ; => "Ns/User"
diff --git a/stdlib/maybe-with-unions.lisp b/stdlib/maybe-with-unions.lisp
new file mode 100644
index 0000000..53a5024
--- /dev/null
+++ b/stdlib/maybe-with-unions.lisp
@@ -0,0 +1,42 @@
+; LIB
+
+(union! Maybe
+    (just value)
+    (nothing))
+
+(let! Maybe/map (\[f m]
+    (match (kind m)
+        "Maybe/Just" (Maybe/just (f (Maybe/Just/get-value m)))
+        "Maybe/Nothing" (Maybe/nothing))))
+
+(let! Maybe/and-then (\[f m]
+    (match (kind m)
+        "Maybe/Just" (f (Maybe/Just/get-value m))
+        "Maybe/Nothing" (Maybe/nothing))))
+
+; TESTING
+
+;; (let! print-line! (\[s]
+;;     (print! (concat s "\n"))))
+
+;; (let! a (Maybe/just 10))
+;; (let! b (Maybe/nothing))
+
+;; (Maybe/map (+ 5) a)
+;; (Maybe/map (+ 5) b)
+
+;; (Maybe/and-then (\[n] (Maybe/just (+ n 5))) a)
+;; (Maybe/and-then (\[n] (Maybe/just (+ n 5))) b)
+
+;; (let! m (Maybe/just 10))
+;; (match m
+;;     (Maybe/just _)
+;;         (print-line! (fmt "found just {0}!" [(Maybe/Just/get-value m)]))
+;;     (Maybe/nothing)
+;;         (print-line! "found nothing!"))
+
+;; (let! m (Maybe/just 10))
+;; (pipe m [
+;;     (Maybe/map (+ 5))
+;;     (Maybe/and-then (\[val] (Maybe/just (- val 3))))
+;; ])
diff --git a/stdlib/maybe.lisp b/stdlib/maybe.lisp
index 07adaee..086b0dc 100644
--- a/stdlib/maybe.lisp
+++ b/stdlib/maybe.lisp
@@ -1,9 +1,9 @@
 ; LIB
 
 (let! Maybe/just (\[a]
-    ["maybe" "just" a]))
+    ["Maybe" "just" a]))
 (let! Maybe/nothing (\[]
-    ["maybe" "nothing"]))
+    ["Maybe" "nothing"]))
 
 (let! Maybe/#at (\[n seq]
     (match seq