Trace messages

Trace messages explain to the user what problem Lean solved and what steps it took. Think of trace messages like a figure in a paper.

They are shown in the editor as a collapsible tree, usually as [class.name] message ▸. Every trace node has a class name, a message, and an array of children. This module provides the API to produce trace messages, the key entry points are:

• registerTraceMessage `class.name registers a trace class
• ``withTraceNode class.name (fun result => return msg) do body produces a trace message containing the trace messages in `body` as children
• trace[class.name] msg produces a trace message without children

Users can enable trace options for a class using set_option trace.class.name true. This only enables trace messages for the class.name trace class as well as child classes that are explicitly marked as inherited (see registerTraceClass).

Internally, trace messages are stored as MessageData: .trace cls msg #[.trace .., .trace ..]

When writing trace messages, try to follow these guidelines:

1. Expansion progressively increases detail. Each level of expansion (of the trace node in the editor) should reveal more details. For example, the unexpanded node should show the top-level goal. Expanding it should show a list of steps. Expanding one of the steps then shows what happens during that step.
2. One trace message per step. The [trace.class] marker functions as a visual bullet point, making it easy to identify the different steps at a glance.
3. Outcome first. The top-level trace message should already show whether the action failed or succeeded, as opposed to a "success" trace message that comes pages later.
4. Be concise. Keep messages short. Avoid repetitive text. (This is also why the editor plugins abbreviate the common prefixes.)
5. Emoji are concisest. Several helper functions in this module help with a consistent emoji language.
6. Good defaults. Setting set_option trace.Meta.synthInstance true (etc.) should produce great trace messages out-of-the-box, without needing extra options to tweak it.

structure Lean.TraceElem : Type

• ref : Lean.Syntax
• msg : Lean.MessageData

instance Lean.instInhabitedTraceElem : Inhabited Lean.TraceElem

Equations

• Lean.instInhabitedTraceElem = { default := { ref := default, msg := default } }

structure Lean.TraceState : Type

• traces : Lean.PersistentArray Lean.TraceElem

instance Lean.instInhabitedTraceState : Inhabited Lean.TraceState

Equations

• Lean.instInhabitedTraceState = { default := { traces := default } }

opaque Lean.inheritedTraceOptions : IO.Ref (Lean.HashSet Lean.Name)

class Lean.MonadTrace (m : Type → Type) : Type

• modifyTraceState : (Lean.TraceState → Lean.TraceState) → m Unit
• getTraceState : m Lean.TraceState

instance Lean.instMonadTrace (m : Type → Type) (n : Type → Type) [inst : MonadLift m n] [inst : Lean.MonadTrace m] : Lean.MonadTrace n

Equations

• Lean.instMonadTrace m n = { modifyTraceState := fun f => liftM (Lean.modifyTraceState f), getTraceState := liftM Lean.getTraceState }

def Lean.printTraces {m : Type → Type} [inst : Monad m] [inst : Lean.MonadTrace m] [inst : MonadLiftT IO m] : m Unit

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def Lean.resetTraceState {m : Type → Type} [inst : Lean.MonadTrace m] : m Unit

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def Lean.isTracingEnabledFor {m : Type → Type} [inst : Monad m] [inst : Lean.MonadOptions m] [inst : MonadLiftT IO m] (cls : Lean.Name) : m Bool

Equations

• Lean.isTracingEnabledFor cls = do let inherited ← liftM (ST.Ref.get Lean.inheritedTraceOptions) let a ← Lean.getOptions pure (Lean.checkTraceOption inherited a cls)

@[inline]

def Lean.getTraces {m : Type → Type} [inst : Monad m] [inst : Lean.MonadTrace m] : m (Lean.PersistentArray Lean.TraceElem)

Equations

• Lean.getTraces = do let s ← Lean.getTraceState pure s.traces

@[inline]

def Lean.modifyTraces {m : Type → Type} [inst : Lean.MonadTrace m] (f : Lean.PersistentArray Lean.TraceElem → Lean.PersistentArray Lean.TraceElem) : m Unit

Equations

• Lean.modifyTraces f = Lean.modifyTraceState fun s => { traces := f s.traces }

@[inline]

def Lean.setTraceState {m : Type → Type} [inst : Lean.MonadTrace m] (s : Lean.TraceState) : m Unit

Equations

• Lean.setTraceState s = Lean.modifyTraceState fun x => s

def Lean.addRawTrace {m : Type → Type} [inst : Monad m] [inst : Lean.MonadTrace m] [inst : Lean.MonadRef m] [inst : Lean.AddMessageContext m] (msg : Lean.MessageData) : m Unit

Equations

• Lean.addRawTrace msg = do let ref ← Lean.getRef let msg ← Lean.addMessageContext msg Lean.modifyTraces fun a => Lean.PersistentArray.push a { ref := ref, msg := msg }

def Lean.addTrace {m : Type → Type} [inst : Monad m] [inst : Lean.MonadTrace m] [inst : Lean.MonadRef m] [inst : Lean.AddMessageContext m] (cls : Lean.Name) (msg : Lean.MessageData) : m Unit

Equations

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@[inline]

def Lean.trace {m : Type → Type} [inst : Monad m] [inst : Lean.MonadTrace m] [inst : MonadLiftT IO m] [inst : Lean.MonadRef m] [inst : Lean.AddMessageContext m] [inst : Lean.MonadOptions m] (cls : Lean.Name) (msg : Unit → Lean.MessageData) : m Unit

Equations

• Lean.trace cls msg = do let a ← Lean.isTracingEnabledFor cls if a = true then Lean.addTrace cls (msg ()) else pure PUnit.unit

@[inline]

def Lean.traceM {m : Type → Type} [inst : Monad m] [inst : Lean.MonadTrace m] [inst : MonadLiftT IO m] [inst : Lean.MonadRef m] [inst : Lean.AddMessageContext m] [inst : Lean.MonadOptions m] (cls : Lean.Name) (mkMsg : m Lean.MessageData) : m Unit

Equations

• Lean.traceM cls mkMsg = do let a ← Lean.isTracingEnabledFor cls if a = true then do let msg ← mkMsg Lean.addTrace cls msg else pure PUnit.unit

def Lean.withTraceNode {α : Type} {m : Type → Type} [inst : Monad m] [inst : Lean.MonadTrace m] [inst : MonadLiftT IO m] [inst : Lean.MonadRef m] [inst : Lean.AddMessageContext m] [inst : Lean.MonadOptions m] {ε : Type} [inst : MonadExcept ε m] (cls : Lean.Name) (msg : Except ε α → m Lean.MessageData) (k : m α) (collapsed : optParam Bool true) : m α

Equations

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def Lean.withTraceNode' {α : Type} {m : Type → Type} [inst : Monad m] [inst : Lean.MonadTrace m] [inst : MonadLiftT IO m] [inst : Lean.MonadRef m] [inst : Lean.AddMessageContext m] [inst : Lean.MonadOptions m] [inst : MonadExcept Lean.Exception m] (cls : Lean.Name) (k : m (α × Lean.MessageData)) (collapsed : optParam Bool true) : m α

Equations

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def Lean.registerTraceClass (traceClassName : Lean.Name) (inherited : optParam Bool false) : IO Unit

Registers a trace class.

By default, trace classes are not inherited; that is, set_option trace.foo true does not imply set_option trace.foo.bar true. Calling registerTraceClass `foo.bar (inherited := true) enables this inheritance on an opt-in basis.

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def Lean.«doElemTrace[_]__» : Lean.ParserDescr

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def Lean.bombEmoji : String

Equations

• Lean.bombEmoji = "💥"

def Lean.checkEmoji : String

Equations

• Lean.checkEmoji = "✅"

def Lean.crossEmoji : String

Equations

• Lean.crossEmoji = "❌"

def Lean.exceptBoolEmoji {ε : Type u_1} : Except ε Bool → String

Equations

• Lean.exceptBoolEmoji _fun_discr = match _fun_discr with | Except.error a => Lean.bombEmoji | Except.ok true => Lean.checkEmoji | Except.ok false => Lean.crossEmoji

def Lean.exceptOptionEmoji {α : Type} {ε : Type u_1} : Except ε (Option α) → String

Equations

• Lean.exceptOptionEmoji _fun_discr = match _fun_discr with | Except.error a => Lean.bombEmoji | Except.ok (some val) => Lean.checkEmoji | Except.ok none => Lean.crossEmoji