CEL.Expr (CEL v0.2.0)

A read-only view of a checked CEL expression, in the spirit of cel-go's common/ast. Get one with CEL.Checked.expr/1.

The view is a tree of node structs, each with the expression's id and its checked type (a CEL.Type.t/0, or nil for a node the checker did not type):

CEL.Expr.Const — a literal.
CEL.Expr.Ident — a variable, type or enum value, by full name.
CEL.Expr.Select — operand.field, has(operand.field) and operand.?field.
CEL.Expr.Call — a function call, operator or enum constructor.
CEL.Expr.MacroCall — a macro as written, such as l.exists(x, p) or cel.bind(v, init, body).
CEL.Expr.ListLiteral, CEL.Expr.MapLiteral and CEL.Expr.MessageLiteral.
CEL.Expr.Comprehension — the loop a macro expands to.

id is the one CEL.Checked.type/2, CEL.Checked.position/2 and CEL.Checked.references/1 use.

Match on the structs to inspect the tree, and use reduce/3, filter/2 or children/1 to walk it. They visit what the author wrote: a MacroCall's target and arguments, not its expansion.

alias CEL.Expr.Call

checked
|> CEL.Checked.expr()
|> CEL.Expr.filter(&match?(%Call{function: "lookup"}, &1))

The view is derived from the checked expression; evaluation does not read it, so it stays stable as the evaluator changes.

Summary

Types

map_entry()

An entry of a CEL.Expr.MapLiteral.

message_field()

A field of a CEL.Expr.MessageLiteral.

scope()

What CEL.Expr.Ident's scope says a name is.

t()

Any node.

type()

A node's checked type, or nil for a node the checker did not type.

Functions

children(comprehension)

Returns the direct children of a node in evaluation order.

filter(node, fun)

Returns the nodes, in visiting order, for which fun returns a truthy value.

reduce(node, acc, fun)

Folds fun over a node and its descendants, visiting each node before its children.