A node is compiled to a runtime node object definition, which stores the details of the node’s observers, dependencies, contexts and various other attributes. However, for efficiency, both in terms of speed and code size, not every single node is actually compiled to a runtime node object. When possible successive nodes are coalesced (merged) into a single node, with a value function that combines the functions of the coalesced nodes.

Node coalescing does not affect the behaviour of a program however it can effect which nodes are actually available when interfacing with other languages.

	Input Nodes, see Section 2.7, “Input Nodes”, are never coalesced into other nodes, as they provide the interface by which a program receives its inputs.

Example. 

a + b -> x
x -> y
y + z -> output

In this example, assuming a, b and z are input nodes and output is an output node, i.e. it has no observers, the following intermediate nodes can all be coalesced into the node output:

As a result, only the following nodes remain:

Node output has the dependencies: a, b and z with the following combined value function:

# y + z
# x + z       
# a + b + z   

a + b + z

When interfacing with Tridash, from another language, only the values of the nodes remaining after coalescing can be observed. The only nodes guaranteed to never be coalesced into other nodes are input nodes, which are explicitly marked as such, and output nodes, that is nodes with no observers.

To allow the value of a node, which is neither an input nor an output node, to be observed, the value of the node’s coalescable attribute can be set to false. This guarantees that the node will never be coalesced into another node, and hence a runtime node object will be created for it.

Example. 

a + b -> x
x -> y
y + z -> output

/attribute(x, coalescable, False) 

In this example, x is guaranteed to never be coalesced into another node and is thus is available for interfacing with other languages.

The value function of output thus becomes x + z, assuming node y is coalesced into x.

	Preventing a node from being coalesced, by setting the coalescable attribute to false, may negatively impact the performance of the program.

	A node with the coalescable attribute set to false, can still be removed if it is not reachable from any input node, and thus its value can never change from its initial value. To prevent the node from being removed, the removable attribute should also be set to false.

	The coalescable and removable attributes have no effect within meta-nodes.