Add project-assertions convenience routine.

FAQ.md

@@ -164,8 +164,8 @@
                          (compile-projection (?! `(posn ,? ,?))))
     ```
     with the same example yields `(set (list ('posn 2 3))`.
-  - `matcher-project/set/single` is like calling `set-first` on the result of
-  `matcher-project/set`
+  - `matcher-project/set/single` is like mapping `car` over the result of
+  `matcher-project/set`. See also `project-assertions`.
   - `patch-project/set` uses `values` to return the result of matching a projection
   against both the added and removed bits of a patch.
 

prospect/core.rkt

@@ -29,6 +29,7 @@
          matcher-project
          matcher-project/set
          matcher-project/set/single
+         project-assertions
 
          event?
          action?

prospect/examples/bank-account.rkt

@@ -19,7 +19,7 @@
 (spawn (lambda (e s)
          (match e
            [(patch added removed)
-            (for [(balance (matcher-project/set/single added (compile-projection (account (?!)))))]
+            (for [(balance (project-assertions added (account (?!))))]
               (printf "Balance changed to ~a\n" balance))
             #f]
            [_ #f]))

prospect/examples/box-and-client.rkt

@@ -18,9 +18,7 @@
 (spawn (lambda (e s)
          (match e
            [(patch added removed)
-            (transition s (for/list [(v (matcher-project/set/single
-                                         added
-                                         (compile-projection (box-state (?!)))))]
+            (transition s (for/list [(v (project-assertions added (box-state (?!))))]
                             (log-info "client: learned that box's value is now ~v" v)
                             (message (set-box (+ v 1)))))]
            [_ #f]))

prospect/examples/chat-simplified-internals.rkt

@@ -73,9 +73,8 @@
 (spawn (lambda (e s)
          (if (patch? e)
              (transition s
-                         (for/list [(id (matcher-project/set/single
-                                         (patch-added e)
-                                         (compile-projection (tcp-remote-open (?!)))))]
+                         (for/list [(id (project-assertions (patch-added e)
+                                                            (tcp-remote-open (?!))))]
                            (spawn-session id)))
              #f))
        (void)

prospect/examples/durable-key-value-store.rkt

@@ -129,7 +129,7 @@
   (spawn (lambda (e s)
            (match e
              [(? patch? p)
-              (define n (matcher-project/set/single (patch-added p) (compile-projection (?!))))
+              (define n (project-assertions (patch-added p) (?!)))
               (for [(b n)] (printf "binding update: ~v\n" b))
               #f]
              [_ #f]))

prospect/examples/key-value-store.rkt

@@ -107,7 +107,7 @@
   (spawn (lambda (e s)
            (match e
              [(? patch? p)
-              (define n (matcher-project/set/single (patch-added p) (compile-projection (?!))))
+              (define n (project-assertions (patch-added p) (?!)))
               (for [(b n)] (printf "binding update: ~v\n" b))
               #f]
              [_ #f]))

prospect/route.rkt

@@ -50,6 +50,7 @@
 	 matcher-key-set/single
          matcher-project/set
          matcher-project/set/single
+         project-assertions ;; composition of matcher-project/set/single with compile-projection
 
 	 ;; Printing and Serialization
 	 pretty-print-matcher
@@ -818,6 +819,10 @@
 (define-syntax-rule (matcher-project/set/single arg ...)
   (matcher-key-set/single (matcher-project arg ...)))
 
+;; Ultra-convenience form.
+(define (project-assertions m . ps)
+  (matcher-project/set/single m (compile-projection* ps)))
+
 ;; struct-type -> Symbol
 ;; Extract just the name of the given struct-type.
 (define (struct-type-name st)