Bend/docs/compilation-and-readback.md

Compilation and readback

How are terms compiled to interaction net nodes?

HVM has a bunch of useful nodes to write IC programs. Every node contains one main port 0 and two auxiliary ports, 1 and 2.

There are 7 kinds of nodes, Eraser, Constructor, Duplicator, Reference, Number, Operation and Match.

A lambda λx x compiles into a Constructor node. An application ((λx x) (λx x)) also compiles into a Constructor node.

  0 - Points to the lambda occurrence      0 - Points to the function
  |                                        |
  λ Lambda                                 @ Application
 / \                                      / \
1   2 - Points to the lambda body        1   2 - Points to the application occurrence
|                                        |
Points to the lambda variable            Points to the argument

When reading back, if we visit a Constructor via port 0 then we know it's a lambda, and if we visit it via port 2 it's an application.

• The Number node uses the label to store it's number.
• An Operation node uses the label to store it's operation.

A duplication let {a b} = x compiles into a Duplicator node. A superposition {a b} compiles to a Duplicator node too. The difference here comes from context too.

  0 - Points to the sup occurrence         0 - Points to the duplicated value
  |                                        |
  # Superposition                          # Duplication
 / \                                      / \
1   2 - Points to the second value       1   2 - Points to the second binding
|                                        |
Points to the first value                Points to the first binding

Check out HVM-Core, one of the Higher Order Company's projects, to know more about this.