About to try writing with types.

typed-parse.rkt

@@ -0,0 +1,6 @@
+#lang typed/racket/base
+(require "typed-structs.rkt")
+(require/typed "parse.rkt"
+               [parse (Any -> Expression)])
+
+(provide parse)

typed-structs.rkt

@@ -0,0 +1,19 @@
+#lang typed/racket/base
+(provide (all-defined-out))
+
+(define-type Expression (U Constant Quote Var Assign Branch Def Lam Seq App))
+(define-struct: Constant ([v : Any]) #:transparent)
+(define-struct: Quote ([v : Any]) #:transparent)
+(define-struct: Var ([id : Symbol]) #:transparent)
+(define-struct: Assign ([id : Symbol]
+                        [expr : Expression]) #:transparent)
+(define-struct: Branch ([test : Expression]
+                        [consequent : Expression]
+                        [alternative : Expression]) #:transparent)
+(define-struct: Def ([id : Symbol] 
+                     [expr : Expression]) #:transparent)
+(define-struct: Lam ([ids : (Listof Symbol)]
+                     [body : Expression]) #:transparent)
+(define-struct: Seq ([es : (Listof Expression)]) #:transparent)
+(define-struct: App ([op : Expression]
+                     [rands : (Listof Expression)]) #:transparent)