SupervisionTree
SupervisionTree — a navigable snapshot of the live supervision tree (ADR 0092).
A SupervisionTree is a thin, immutable wrapper over a flat
List(SupervisionNode) plus the parent/child adjacency captured at snapshot
time. It is the high-level view layered on the flat records: the full
collection protocol (do:, select:, detect:, collect:) plus tree
navigation (root, nodesOfKind:, findClass:). Reach one via
ProcessNavigation default tree or the Workspace processes alias.
The snapshot is best-effort point-in-time: iterating a tree never re-enters OTP (it is frozen), so the walk is internally consistent. To observe change, take a new snapshot.
Examples
tree := ProcessNavigation default tree
tree root // => the snapshot root SupervisionNode
tree size // => total node count
tree do: [:node | Transcript showLine: node printString]
tree select: [:node | node isSupervisor]
tree nodesOfKind: #beamtalkActor // => List(SupervisionNode)
tree findClass: Counter // => List(SupervisionNode) for Counter actors
Methods
Instance Methods
The flat list of nodes, each enriched so parent/child navigation works.
This is the flat record API the ADR exposes; root is the navigable
head layered on top.
Examples
tree nodes // => #(a SupervisionNode, ...)
The snapshot root — the first node with no parent — or nil for an empty
snapshot.
Note: the default / system snapshot can be a forest (the app root,
workspace-attached supervisors, and standalone supervised trees are each
parentless). root returns the first such root; iterate nodes (or
select: [:n | n parentPid isNil]) to reach every root in a forest.
Examples
tree root // => a SupervisionNode | nil
Total number of nodes in the snapshot.
Examples
tree size // => 6
Whether the snapshot is empty.
Examples
tree isEmpty // => false
Pre-order walk: evaluate aBlock for every node in the snapshot.
Examples
tree do: [:node | Transcript showLine: node printString]
The nodes for which aBlock answers true.
Examples
tree select: [:node | node isSupervisor]
The first node for which aBlock answers true. Raises if none match —
use detect:ifNone: for a default.
Examples
tree detect: [:node | node registeredName == #DatabasePool]
The first node for which aBlock answers true, or the value of
noneBlock if none match.
Examples
tree detect: [:n | n isSupervisor] ifNone: [nil]
Collect the result of applying aBlock to every node.
Examples
tree collect: [:node | node registeredName]
The nodes whose kind equals aKind (e.g. #beamtalkActor,
#otpProcess).
Examples
tree nodesOfKind: #beamtalkActor // => List(SupervisionNode)
The nodes backed by the Beamtalk class aClass — every running instance of
that class in the supervision tree.
Examples
tree findClass: Counter // => List(SupervisionNode) for Counter actors
A serialisable form of the snapshot — one Dictionary per node carrying
its identity, kind, class, child count, and parent linkage (adjacency).
This is the cross-surface wire form (ADR 0092 Implementation §5): the MCP
and LiveView/browser surfaces render this structure so every surface shows
equivalent data. Pids are rendered as Strings (JSON-stable); parentPid
reconstructs the tree.
Examples
ProcessNavigation default tree asDictionaries
// => #(#{#pid => "<0.200.0>", #kind => #beamtalkSupervisor, ...}, ...)
Human-readable summary, e.g. #SupervisionTree<6 nodes, root: #AppSup> or
#SupervisionTree<empty>.
Examples
Workspace processes printString // => "#SupervisionTree<3 nodes, root: #AppSup>"
Inherited Methods
From Value
Return a developer-readable string representation showing fields.
Produces ClassName(field: value, ...) via the canonical structural
renderer (ADR 0094). Field values are rendered with their own
printString (strings stay quoted, nested values show their structural
form), in sorted field order. A class with no fields produces
ClassName(). Recursion is bounded by depth/width/length caps with a
cycle guard.
Examples
ValuePoint x: 3 y: 4 printString // => "ValuePoint(x: 3, y: 4)"
ValuePoint new printString // => "ValuePoint(x: 0, y: 0)"
From Object
Return the class of the receiver.
Examples
42 class // => Integer
"hello" class // => String
Test if the receiver is nil. Returns false for all objects except nil.
Examples
42 isNil // => false
nil isNil // => true
Test if the receiver is not nil. Returns true for all objects except nil.
Examples
42 notNil // => true
nil notNil // => false
If the receiver is nil, evaluate nilBlock. Otherwise return self.
Examples
42 ifNil: [0] // => 42
nil ifNil: [0] // => 0
If the receiver is not nil, evaluate notNilBlock with self.
Examples
42 ifNotNil: [:v | v + 1] // => 43
nil ifNotNil: [:v | v + 1] // => nil
If nil, evaluate nilBlock; otherwise evaluate notNilBlock with self.
Examples
42 ifNil: [0] ifNotNil: [:v | v + 1] // => 43
nil ifNil: [0] ifNotNil: [:v | v + 1] // => 0
If not nil, evaluate notNilBlock with self; otherwise evaluate nilBlock.
Examples
42 ifNotNil: [:v | v + 1] ifNil: [0] // => 43
nil ifNotNil: [:v | v + 1] ifNil: [0] // => 0
Return the developer-readable (Debug) string representation.
printString is the Debug protocol (ADR 0094): the self-describing,
structural form used by the REPL, logs, and by any other printString
that nests this object. It is the REPL default — evaluating an expression
shows its printString.
This default returns the bare class name (no a/an article — the
old "a ClassName" form was dropped in ADR 0094). Value overrides it
with the structural ClassName(field: value, ...) form, actors render as
Actor(ClassName, pid), supervisors as Supervisor(ClassName, pid) /
DynamicSupervisor(ClassName, pid), and primitive types (Integer, String,
List, …) override it with their own richer output. Authors rarely override
printString directly — the default is derived.
Examples
42 printString // => "42"
Return the user-facing (Display) string representation.
displayString is the Display protocol (ADR 0094): the human-facing
form. It is the hook the language pulls during string interpolation —
every {...} segment renders via the value's displayString. Developers
rarely call it directly; they override it when a value has a natural
human rendering (e.g. Money → $10.50, where printString would still
show the Debug form).
It defaults to printString, so most types need no override. String
and Symbol demonstrate the split: "hi" printString → "\"hi\""
(quoted, Debug) while "hi" displayString → "hi" (plain, Display);
likewise #foo drops its # prefix under displayString.
displayString is not part of the Printable protocol (deferred per
ADR 0094 §5).
Examples
42 displayString // => "42"
Open a navigable Inspector cursor on the receiver.
ADR 0095 Phase 3 (BT-2504). inspect is repurposed from -> String
(the ADR-0094 deferral) to the verb that produces an Inspector — a
live, immutable cursor for drilling into the object (Inspector on: self).
anObject inspect is the shorthand; Inspector on: anObject is the
explicit spelling. The cursor exposes fields/at:/path/refresh/
printString (an indented text tree) and asDictionaries (the MCP/browser
wire form); see Inspector.
This is a breaking change: code that used inspect for its old
String result must switch to printString (the structural Debug string,
ADR 0094) — a transitional lint flags inspect used directly in ++/
string position.
Examples
42 inspect kind // => #value
(Point x: 3 y: 4) inspect fields size // => 2
(Point x: 3 y: 4) printString // => "Point(x: 3, y: 4)" (the old inspect string)
Return the receiver itself. Useful for cascading side effects.
Examples
42 yourself // => 42
Return a hash value for the receiver.
Examples
42 hash
Test if the receiver responds to the given selector.
Examples
42 respondsTo: #abs // => true
Return the names of fields.
Examples
42 fieldNames // => #()
Return the value of the named field.
Examples
object fieldAt: #name
Set the value of the named field (returns new state).
Examples
object fieldAt: #name put: "Alice"
Send a unary message dynamically.
Examples
42 perform: #abs // => 42
Send a message dynamically with arguments.
Examples
3 perform: #max: withArguments: #(5) // => 5
Raise an error indicating this method must be overridden by a subclass.
Examples
self subclassResponsibility
Raise an error indicating this method has not yet been implemented.
Use this for work-in-progress stubs. Distinct from subclassResponsibility,
which signals an interface contract violation.
Examples
self notImplemented
Send aValue to the current transcript without a trailing newline.
Nil-safe: does nothing when no transcript is set (batch compile, tests).
Examples
42 show: "value: "
Send aValue to the current transcript followed by a newline.
Nil-safe: does nothing when no transcript is set (batch compile, tests).
Examples
42 showCr: "hello world"
Test if the receiver is an instance of aClass or any of its subclasses.
For class-object receivers, follows Smalltalk semantics: self class
is the metaclass, so the check walks the parallel metaclass hierarchy.
The parallel chain is grounded at ProtoObject class superclass == Class
(ADR 0036), so the metaclass tower merges into the instance-side
Class → Behaviour → Object → ProtoObject chain. As a result,
Integer isKindOf: Object and Integer isKindOf: Class both return true.
Examples
42 isKindOf: Integer // => true
42 isKindOf: Object // => true
#foo isKindOf: Symbol // => true
#foo isKindOf: String // => false
Integer isKindOf: Number // => false (metaclass chain, not instance chain)
Integer isKindOf: Number class // => true (Number class is in the parallel chain)
Integer isKindOf: Object // => true (grounded — Object is reachable via the metaclass tower)
Integer isKindOf: Class // => true (Integer class inherits from Class)
Raise an error with the given message.
Examples
self error: "something went wrong"
Delegate message dispatch to the backing Erlang module (ADR 0101, BT-2720).
This method is a sentinel — a plain Object has no backing Erlang module,
so calling delegate raises an Error at runtime. Stateless Objects
declared with native: have their self delegate method bodies rewritten
by the compiler's codegen phase to call the backing module directly, so the
sentinel is never reached on a native: class.
Unlike Actor's delegate (visible only to Actor subclasses), this
Object-base sentinel is visible to every class, so delegate is a
reserved selector on the Object protocol.
Examples
42 delegate // => ERROR: delegate called on a non-native Object
From ProtoObject
Test value equality (Erlang ==).
Examples
42 == 42 // => true
"abc" == "abc" // => true
Test value inequality (negation of ==).
Examples
1 /= 2 // => true
42 /= 42 // => false
Return the class of the receiver.
Examples
42 class // => Integer
"hello" class // => String
Handle messages the receiver does not understand. Override for custom dispatch.
Examples
42 unknownMessage // => ERROR: does_not_understand
Send a message dynamically with an arguments list.
Examples
42 perform: #abs withArguments: #() // => 42
Execute a class method in the caller's process, bypassing gen_server dispatch.
The caller takes responsibility for knowing the method does not mutate class state. Useful for long-running class methods that would otherwise block the class object's gen_server.
Limitations: only resolves methods defined directly on the target class
module (does not walk the superclass chain). Class variables and self
are not available to the method (nil and #{} are passed).
Examples
MyClass performLocally: #run:ctx: withArguments: #(input, ctx)
Send a message dynamically with an arguments list and explicit timeout.
The timeout (in milliseconds or #infinity) applies to the gen_server:call
when the receiver is an actor. For value types, timeout is ignored.
Examples
actor perform: #query withArguments: #(sql) timeout: 30000