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Visitor[State: Any #read]

[Source]

Used to effect transformations of an AST, using SyntaxTree.traverse().

AST trees are immutable. We get a transformed tree by traversing the old tree and returning a new one (re-using unmodified nodes as necessary).

Traversal happens in the following fashion:

  • For a node (starting with the root):
  • Call visit_pre() on the visitor with a parent state; this returns an intermediate state (if some data needs to be saved for later).
  • Build a list of new node children by calling traverse() on each old child, passing the the intermediate state.
  • Call visit_post() with the intermediate state, the list of child states (returned from each child's visit_post()), the new children, and a map from old to new children. visit_post() then returns the intermediate state and the new node.
interface ref Visitor[State: Any #read]

Public Functions

visit_pre

[Source]

Returns an intermediate state value for use when constructing the new node.

fun ref visit_pre(
  parent_state: State,
  node: Node val,
  path: (Cons[Node val] val | Nil[Node val] val),
  errors: Array[(Node val , String val)] iso)
: (State , Array[(Node val , String val)] iso^)

Parameters

Returns

visit_post

[Source]

Returns a new node constructed from the "pre" state (the intermediate state) that was returned by visit_pre(), and the new children.

Even if no other processing is needed, make sure to clone the node if new_children and update_map exist.

fun ref visit_post(
  node_state: State,
  node: Node val,
  path: (Cons[Node val] val | Nil[Node val] val),
  errors: Array[(Node val , String val)] iso,
  child_states: (ReadSeq[State] box | None val),
  new_children: (ReadSeq[Node val] val | None val),
  update_map: (HashMap[Node val, Node val, HashIs[Node val] val] val | None val))
: (State , (Node val | None val) , Array[(Node val , String val)] iso^)

Parameters

Returns