Added terminal sc contracts, and made optimizer use them.

pkgs/typed-racket-pkgs/typed-racket-lib/typed-racket/static-contracts/combinators/lengths.rkt

@@ -35,6 +35,8 @@
          [(define (sc-map v f) v)
           (define (sc->contract v f) (length-contract-syntax v))
           (define (sc->constraints v f) 'flat)]
+        #:methods gen:terminal-sc
+         [(define (terminal-sc-kind v) 'flat)]
         #:methods gen:custom-write [(define write-proc length-contract-write-proc)])
 
 (define (list-length/sc n)

pkgs/typed-racket-pkgs/typed-racket-lib/typed-racket/static-contracts/combinators/simple.rkt

@@ -37,6 +37,8 @@
          [(define (sc-map v f) v)
           (define (sc->contract v f) (simple-contract-syntax v))
           (define (sc->constraints v f) (simple-contract-restrict (simple-contract-kind v)))]
+        #:methods gen:terminal-sc
+         [(define (terminal-sc-kind v) (simple-contract-kind v))]
         #:methods gen:custom-write [(define write-proc simple-contract-write-proc)])
 
 (define (flat/sc ctc) (simple-contract ctc 'flat))

pkgs/typed-racket-pkgs/typed-racket-lib/typed-racket/static-contracts/optimize.rkt

@@ -78,7 +78,7 @@
     [(arr/sc: args rest (list (any/sc:) ...))
      (arr/sc args rest #f)]
     [(none/sc:) any/sc]
-    [(? flat/sc?) any/sc]
+    [(app terminal-sc-kind 'flat) any/sc]
     [else sc]))
 
 

pkgs/typed-racket-pkgs/typed-racket-lib/typed-racket/static-contracts/structures.rkt

@@ -17,12 +17,14 @@
     [sc-map (static-contract? (static-contract? variance/c . -> . static-contract?) . -> . static-contract?)]
     [sc->contract (static-contract? (static-contract? . -> . syntax?) . -> . syntax?)]
     [sc->constraints (static-contract? (static-contract? . -> . contract-restrict?) . -> . contract-restrict?)]
+    [terminal-sc-kind (static-contract? . -> . (or/c #f contract-kind?))]
     [sc? predicate/c]
     )
 
 
   prop:combinator-name
-  gen:sc)
+  gen:sc
+  gen:terminal-sc)
 
 (define variance/c (or/c 'covariant 'contravariant 'invariant))
 
@@ -103,6 +105,16 @@
   ;; The function argument should be used for sub parts of the static contract.
   [sc->constraints sc f])
 
+;; Functionality that terminal static contracts should support
+;; Terminal static contracts are ones without any sub static contracts
+(define-generics terminal-sc
+  ;; terminal-sc-kind: terminal-static-contract? -> (or/c #f contract-kind?)
+  ;; Returns the kind of contract that this represents
+  ;; Returns #f if it is not a terminal contract
+  [terminal-sc-kind terminal-sc]
+  #:defaults ([(λ (v) #t)
+               (define (terminal-sc-kind v)  #f)]))
+
 ;; Super struct of static contracts
 (struct static-contract ()
         #:transparent