Create a named jump function.

Add a function `step.jump` to make explicit the action performed when
passing in a function in the cadence. Using an existing function is too
clever, I believe.

See: https://github.com/bigeasy/cadence/blob/master/diary.md#jumping-the-parent

Closes #102.

File                             Raw         Min         Zip     Min/Zip
index.js                 10926/10.67  3535/03.45  3128/03.05  1332/01.30

index.js

@@ -61,24 +61,6 @@ function cadence () {
       return;
     }
 
-    // If our first argument is a function, we check to see if it is a jump
-    // instruction. If the function is a member of the current cadence, we
-    // will invoke that function with the results of this step.
-
-    // Search for the function in the current cadence.
-    if (vargs.length == 1 && typeof vargs[0] == "function") {
-      for (i = invocations[0].args[0].length - 1;
-           i > -1 && invocations[0].args[0][i] !== vargs[0]; i--) {}
-    }
-
-    // If we find the function in the current cadence, we set the index of
-    // next step function to execute; then remove the function argument and
-    // proceed.
-    if (~i) {
-      invocations[0].args[1] = i;
-      vargs.shift();
-    }
-
     var callback = { errors: [], results: [] };
     var fixup;
     if (fixup = (vargs[0] === async)) {
@@ -122,6 +104,22 @@ function cadence () {
     return createHandler.apply({ event: true }, [0, []].concat(__slice.call(arguments)))
   }
 
+  async.jump = function (label) {
+    // If our first argument is a function, we check to see if it is a jump
+    // instruction. If the function is a member of the current cadence, we
+    // will invoke that function with the results of this step.
+
+    // Search for the function in the current cadence. If we find the function
+    // in the current cadence, we set the index of next step function to
+    // execute; then remove the function argument and proceed.
+    for (var i = 0, I = invocations[0].args[0].length; i < I; i++) {
+      if (invocations[0].args[0][i] === label) {
+        invocations[0].args[1] = i;
+        return;
+      }
+    }
+  }
+
   // Create a sub-cadence.
   function createCadence (invocation, callback) {
     var index = 0;

t/cadence/jump.t.js

@@ -10,10 +10,11 @@ require('proof')(1, function (equal) {
     }, inc = function (count) {
       step()(null, count + 1);
     }, function (count) {
-      if (count != 10) step(inc)(null, count);
-      else return count;
+      if (count != 10) step.jump(inc);
+      return count;
     });
   })(function (error, result) {
+    if (error) throw error;
     equal(result, 10, "jump");
   });
 });