Document constant functions

docs/contracts.rst

@@ -421,9 +421,9 @@ change by overriding).
 
 .. index:: ! constant
 
-**********
+************************
-Constants
+Constant State Variables
-**********
+************************
 
 State variables can be declared as constant (this is not yet implemented
 for array and struct types and not possible for mapping types).
@@ -442,6 +442,27 @@ for these variables and every occurrence is replaced by their constant value.
 
 The value expression can only contain integer arithmetics.
 
+******************
+Constant Functions
+******************
+
+Functions can be declared constant. These functions promise not to modify the state.
+
+::
+
+    pragma solidity ^0.4.0;
+
+    contract C {
+        function f(uint a, uint b) constant returns (uint) {
+            return a * (b + 42);
+        }
+    }
+
+.. note::
+  Accessor methods are marked constant.
+
+.. warning::
+  The compiler does not enforce yet that a constant method is not modifying state.
 
 .. index:: ! fallback function, function;fallback
 

docs/frequently-asked-questions.rst

@@ -97,20 +97,6 @@ Its type is the type of the contract. Since any contract type basically inherits
 ``address`` type, ``this`` is always convertible to ``address`` and in this case contains
 its own address.
 
-What is the difference between a function marked ``constant`` and one that is not?
-==================================================================================
-
-``constant`` functions can perform some action and return a value, but cannot
-change state (this is not yet enforced by the compiler). In other words, a
-constant function cannot save or update any variables within the contract or wider
-blockchain. These functions are called using ``c.someFunction(...)`` from
-geth or any other web3.js environment.
-
-"non-constant" functions (those lacking the ``constant`` specifier) must be called
-with ``c.someMethod.sendTransaction({from:eth.accounts[x], gas: 1000000});``
-That is, because they can change state, they have to have a gas
-payment sent along to get the work done.
-
 Get a contract to return its funds to you (not using ``selfdestruct(...)``).
 ============================================================================