documentation

2 files changed, 14 insertions, 2 deletions

diff --git a/cond-thunk.egg b/cond-thunk.egg
index 1472c7f..36f472b 100644
--- a/cond-thunk.egg
+++ b/cond-thunk.egg
@@ -1,5 +1,5 @@
 ((author "Peter McGoron")
- (version "0.2.0")
+ (version "0.2.1")
  (synopsis "macros for abstracting conditional branches")
  (category "lang-exts")
  (license "Apache-2.0")
diff --git a/doc/mcgoron.cond-thunk.values.scm b/doc/mcgoron.cond-thunk.values.scm
index c319f3d..4067594 100644
--- a/doc/mcgoron.cond-thunk.values.scm
+++ b/doc/mcgoron.cond-thunk.values.scm
@@ -3,7 +3,8 @@
   (subsigs
    (clause (pattern
             ((when conditional))
-            ((let value => formal)))))
+            ((let value => formal))
+            ((on-error! expr)))))
   (desc "
 For each clause,
 
@@ -14,6 +15,17 @@ For each clause,
   `value` returns no values, then the `after` expression returns `#f`.
   Otherwise, the values returned are bound to `formal` in the next clauses
   and in the body.
+* If `clause` is `on-error! expr`, then the next failed clause will execute
+  `expr`. The expression will be executed in the scope of all previous
+  declarations.
+  
+  The `on-error!` clause works by returning the result thunk to any
+  enclosing `cond-thunk` expression before the next clauses are evaluated.
+  The execution of the rest of the clauses continues in the returned thunk,
+  with failures tail-calling a thunk that executes `expr`. The `on-error!`
+  clause is simliar to `cut` in logic programming languages, because it
+  prevents backtracking to an enclosing `cond-thunk`. It was originally
+  called `cut!`.
 
 Once all clauses succeed, the `after` clause returns a thunk containing
 body. The free variables bound in and surrounding the `after` expression