add structure-capture bit to FAQ

2015-10-20 08:34:34 -04:00 · 2015-10-20 08:34:34 -04:00 · d23d487849
parent 4cb6f5cf26
commit d23d487849
1 changed files with 8 additions and 0 deletions
--- a/FAQ.md
+++ b/FAQ.md
@ -156,6 +156,14 @@
                         (compile-projection `(posn ,? ,(?!))))
    ```
    and get the result `(set (list 3))`.
+  - an entire structure can be captured by passing a pattern as an argument to
+    `(?!)`.
+
+    ```racket
+    (matcher-project/set (patch-added p)
+                         (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`
  - `patch-project/set` uses `values` to return the result of matching a projection