diff --git a/solidity.html.markdown b/solidity.html.markdown
index 71a44b92..3a5e8ff5 100644
--- a/solidity.html.markdown
+++ b/solidity.html.markdown
@@ -506,7 +506,8 @@ function remove() {
// Steps: 1. Commit to something, 2. Reveal commitment
sha3("some_bid_amount", "some secret"); // commit
-// call contract's reveal function showing bid plus secret that hashes to SHA3
+// call contract's reveal function in the future
+// showing bid plus secret that hashes to SHA3
reveal(100, "mySecret");
// B. Storage optimization
@@ -531,7 +532,45 @@ reveal(100, "mySecret");
// Contracts must be manually called to handle time-based scheduling; can create external
// code to regularly ping, or provide incentives (ether) for others to
-// E. State machines
+// E. Observer Pattern
+// An Observer Pattern lets you register as a subscriber and
+// register a function which is called by the oracle (note, the oracle pays
+// for this action to be run)
+// Some similarities to subscription in Pub/sub
+
+// This is an abstract contract, both client and server classes import
+// the client should implement
+contract SomeOracleCallback {
+ function oracleCallback(int _value, uint _time, bytes32 info) external;
+}
+
+contract SomeOracle {
+ SomeOracleCallback[] callbacks; // array of all subscribers
+
+ // Register subscriber
+ function addSubscriber(SomeOracleCallback a) {
+ callbacks.push(a);
+ }
+
+ function notify(value, time, info) private {
+ for(uint i = 0;i < callbacks.length; i++) {
+ // all called subscribers must implement the oracleCallback
+ callbacks[i].oracleCallback(value, time, info);
+ }
+ }
+
+ function doSomething() public {
+ // Code to do something
+
+ // Notify all subscribers
+ notify(_value, _time, _info);
+ }
+}
+
+// Now, your client contract can addSubscriber by importing SampleOracleCallback
+// and registering with Sample Oracle
+
+// F. State machines
// see example below for State enum and inState modifier
@@ -748,7 +787,7 @@ someContractAddress.callcode('function_name');
- Libraries
## Style
-- Python's [PEP8](https://www.python.org/dev/peps/pep-0008/) is used as the baseline style guide, including its general philosophy)
+- Python's [PEP8](https://www.python.org/dev/peps/pep-0008/) is used as the baseline style guide, including its general philosophy
## Future To Dos
- New keywords: protected, inheritable