Nodes

This page describes the structure of the AST ("abstract syntax tree") of COL ("common object language").

Definition

Let's start by looking at the anatomy of a node:

• final: It's not encouraged to further specialize the behaviour of a node, so we mark concrete nodes final.
• case class: We maintain the invariant that equal nodes are semantically equivalent. For most nodes, this means that they should define equality structurally, which is implicit for case classes.
• FloorDiv: Node names should be short but descriptive. Too long: FlooringDivision, too short: FDiv, okay: FlooringDiv.
• [G]: A type parameter without concrete meaning: it should be propagated into all subnodes.
• (left: Expr[G], right: Expr[G]): the properties and subnodes of the node. For case classes it is not necessary to specify val in the first parameter list.
• (val blame: Blame[DivByZero]): nodes that are responsible for an error can optionally have an extra parameter list with one blame parameter.
• (implicit val o: Origin): origins loosely describe the reason a node is in the tree. One simple reason is that it existed in the supplied files.
• extends Expr[G]: denotes the node family the node belongs to, in this case the expressions.
• with FloorDivImpl[G]: to keep the file shorter, the implementation of nodes is moved into a trait in a different file.