Control.Monad.Trace.Class

The MonadTrace class

Generating traces

class Monad m => MonadTrace m where

A monad capable of generating traces.

There are currently two instances of this monad:

• TraceT, which emits spans for each trace in IO and is meant to be used in production.
• Identity, where tracing is a no-op and allows testing traced functions without any overhead or complex setup.

Minimal complete definition

trace

Methods

trace :: Builder -> m a -> m a

Trace an action, wrapping it inside a new span.

activeSpan :: m (Maybe Span)

Extracts the currently active span, or Nothing if the action is not being traced.

activeSpan :: (MonadTrace n, MonadTrans t, m ~ t n) => m (Maybe Span)

Extracts the currently active span, or Nothing if the action is not being traced.

addSpanEntry :: Key -> Value -> m ()

Adds information to the active span, if present.

addSpanEntry :: (MonadTrace n, MonadTrans t, m ~ t n) => Key -> Value -> m ()

Adds information to the active span, if present.

Instances

MonadTrace Identity

Defined in Control.Monad.Trace.Class

Methods

trace :: Builder -> Identity a -> Identity a

activeSpan :: Identity (Maybe Span)

addSpanEntry :: Key -> Value -> Identity ()

MonadUnliftIO m => MonadTrace (TraceT m)

Defined in Control.Monad.Trace

Methods

trace :: Builder -> TraceT m a -> TraceT m a

activeSpan :: TraceT m (Maybe Span)

addSpanEntry :: Key -> Value -> TraceT m ()

(Monad m, MonadTrace m) => MonadTrace (ExceptT e m)

Defined in Control.Monad.Trace.Class

Methods

trace :: Builder -> ExceptT e m a -> ExceptT e m a

activeSpan :: ExceptT e m (Maybe Span)

addSpanEntry :: Key -> Value -> ExceptT e m ()

(Monad m, MonadTrace m) => MonadTrace (StateT s m)

Defined in Control.Monad.Trace.Class

Methods

trace :: Builder -> StateT s m a -> StateT s m a

activeSpan :: StateT s m (Maybe Span)

addSpanEntry :: Key -> Value -> StateT s m ()

(Monad m, MonadTrace m) => MonadTrace (StateT s m)

Defined in Control.Monad.Trace.Class

Methods

trace :: Builder -> StateT s m a -> StateT s m a

activeSpan :: StateT s m (Maybe Span)

addSpanEntry :: Key -> Value -> StateT s m ()

(Monad m, MonadTrace m, Monoid w) => MonadTrace (WriterT w m)

Defined in Control.Monad.Trace.Class

Methods

trace :: Builder -> WriterT w m a -> WriterT w m a

activeSpan :: WriterT w m (Maybe Span)

addSpanEntry :: Key -> Value -> WriterT w m ()

(Monad m, MonadTrace m, Monoid w) => MonadTrace (WriterT w m)

Defined in Control.Monad.Trace.Class

Methods

trace :: Builder -> WriterT w m a -> WriterT w m a

activeSpan :: WriterT w m (Maybe Span)

addSpanEntry :: Key -> Value -> WriterT w m ()

(Monad m, MonadTrace m) => MonadTrace (ReaderT r m)

Defined in Control.Monad.Trace.Class

Methods

trace :: Builder -> ReaderT r m a -> ReaderT r m a

activeSpan :: ReaderT r m (Maybe Span)

addSpanEntry :: Key -> Value -> ReaderT r m ()

(Monad m, MonadTrace m, Monoid w) => MonadTrace (RWST r w s m)

Defined in Control.Monad.Trace.Class

Methods

trace :: Builder -> RWST r w s m a -> RWST r w s m a

activeSpan :: RWST r w s m (Maybe Span)

addSpanEntry :: Key -> Value -> RWST r w s m ()

(Monad m, MonadTrace m, Monoid w) => MonadTrace (RWST r w s m)

Defined in Control.Monad.Trace.Class

Methods

trace :: Builder -> RWST r w s m a -> RWST r w s m a

activeSpan :: RWST r w s m (Maybe Span)

addSpanEntry :: Key -> Value -> RWST r w s m ()

data Span

A part of a trace.

Constructors

Span

Fields

• spanName :: !Name
• spanContext :: !Context
• spanReferences :: !(Set Reference)
• spanIsSampled :: !Bool
• spanIsDebug :: !Bool

data Context

A fully qualified span identifier, containing both the ID of the trace the span belongs to and the span's ID. Span contexts can be exported (resp. imported) via their toJSON (resp. fromJSON) instance.

Constructors

Context

Fields

• contextTraceID :: !TraceID
• contextSpanID :: !SpanID
• contextBaggages :: !(Map Key ByteString)

Instances

Eq Context

Defined in Control.Monad.Trace.Internal

Methods

(==) :: Context -> Context -> Bool

(/=) :: Context -> Context -> Bool

Ord Context

Defined in Control.Monad.Trace.Internal

Methods

compare :: Context -> Context -> Ordering

(<) :: Context -> Context -> Bool

(<=) :: Context -> Context -> Bool

(>) :: Context -> Context -> Bool

(>=) :: Context -> Context -> Bool

max :: Context -> Context -> Context

min :: Context -> Context -> Context

Show Context

Defined in Control.Monad.Trace.Internal

Methods

showsPrec :: Int -> Context -> ShowS

show :: Context -> String

showList :: [Context] -> ShowS

newtype TraceID

A 128-bit trace identifier.

Constructors

TraceID ByteString

Instances

Eq TraceID

Defined in Control.Monad.Trace.Internal

Methods

(==) :: TraceID -> TraceID -> Bool

(/=) :: TraceID -> TraceID -> Bool

Ord TraceID

Defined in Control.Monad.Trace.Internal

Methods

compare :: TraceID -> TraceID -> Ordering

(<) :: TraceID -> TraceID -> Bool

(<=) :: TraceID -> TraceID -> Bool

(>) :: TraceID -> TraceID -> Bool

(>=) :: TraceID -> TraceID -> Bool

max :: TraceID -> TraceID -> TraceID

min :: TraceID -> TraceID -> TraceID

Show TraceID

Defined in Control.Monad.Trace.Internal

Methods

showsPrec :: Int -> TraceID -> ShowS

show :: TraceID -> String

showList :: [TraceID] -> ShowS

ToJSON TraceID

Defined in Control.Monad.Trace.Internal

Methods

toJSON :: TraceID -> Value

toEncoding :: TraceID -> Encoding

toJSONList :: [TraceID] -> Value

toEncodingList :: [TraceID] -> Encoding

FromJSON TraceID

Defined in Control.Monad.Trace.Internal

Methods

parseJSON :: Value -> Parser TraceID

parseJSONList :: Value -> Parser [TraceID]

encodeTraceID :: TraceID -> Text

Hex-encodes a trace ID.

decodeTraceID :: Text -> Maybe TraceID

Decodes a traced ID from a hex-encoded string.

newtype SpanID

A 64-bit span identifier.

Constructors

SpanID ByteString

Instances

Eq SpanID

Defined in Control.Monad.Trace.Internal

Methods

(==) :: SpanID -> SpanID -> Bool

(/=) :: SpanID -> SpanID -> Bool

Ord SpanID

Defined in Control.Monad.Trace.Internal

Methods

compare :: SpanID -> SpanID -> Ordering

(<) :: SpanID -> SpanID -> Bool

(<=) :: SpanID -> SpanID -> Bool

(>) :: SpanID -> SpanID -> Bool

(>=) :: SpanID -> SpanID -> Bool

max :: SpanID -> SpanID -> SpanID

min :: SpanID -> SpanID -> SpanID

Show SpanID

Defined in Control.Monad.Trace.Internal

Methods

showsPrec :: Int -> SpanID -> ShowS

show :: SpanID -> String

showList :: [SpanID] -> ShowS

ToJSON SpanID

Defined in Control.Monad.Trace.Internal

Methods

toJSON :: SpanID -> Value

toEncoding :: SpanID -> Encoding

toJSONList :: [SpanID] -> Value

toEncodingList :: [SpanID] -> Encoding

FromJSON SpanID

Defined in Control.Monad.Trace.Internal

Methods

parseJSON :: Value -> Parser SpanID

parseJSONList :: Value -> Parser [SpanID]

encodeSpanID :: SpanID -> Text

Hex-encodes a span ID.

decodeSpanID :: Text -> Maybe SpanID

Decodes a span ID from a hex-encoded string.

data Reference

A relationship between spans.

There are currently two types of references, both of which model direct causal relationships between a child and a parent. More background on references is available in the opentracing specification: https://github.com/opentracing/specification/blob/master/specification.md.

Constructors

ChildOf !SpanID

ChildOf references imply that the parent span depends on the child span in some capacity. Note that this reference type is only valid within a single trace.

FollowsFrom !Context

If the parent does not depend on the child, we use a FollowsFrom reference.

Instances

Eq Reference

Defined in Control.Monad.Trace.Internal

Methods

(==) :: Reference -> Reference -> Bool

(/=) :: Reference -> Reference -> Bool

Ord Reference

Defined in Control.Monad.Trace.Internal

Methods

compare :: Reference -> Reference -> Ordering

(<) :: Reference -> Reference -> Bool

(<=) :: Reference -> Reference -> Bool

(>) :: Reference -> Reference -> Bool

(>=) :: Reference -> Reference -> Bool

max :: Reference -> Reference -> Reference

min :: Reference -> Reference -> Reference

Show Reference

Defined in Control.Monad.Trace.Internal

Methods

showsPrec :: Int -> Reference -> ShowS

show :: Reference -> String

showList :: [Reference] -> ShowS

rootSpan :: MonadTrace m => Sampling -> Name -> m a -> m a

Starts a new trace.

rootSpanWith :: MonadTrace m => (Builder -> Builder) -> Sampling -> Name -> m a -> m a

Starts a new trace, customizing the span builder. Note that the sampling input will override any sampling customization set on the builder.

childSpan :: MonadTrace m => Name -> m a -> m a

Extends a trace if it is active, otherwise do nothing.

childSpanWith :: MonadTrace m => (Builder -> Builder) -> Name -> m a -> m a

Extends a trace if it is active, otherwise do nothing. The active span's ID will be added as a reference to the new span and it will share the same trace ID (overriding any customization done to the builder).

Customizing spans

data Builder

A trace builder.

Note that Builder has an IsString instance, producing a span with the given string as name, no additional references, tags, or baggages. This allows convenient creation of spans via the OverloadedStrings pragma.

Constructors

Builder

Fields

• builderName :: !Name

  Name of the generated span.

• builderTraceID :: !(Maybe TraceID)

  The trace ID of the generated span. If unset, the active span's trace ID will be used if present, otherwise a new ID will be generated.

• builderSpanID :: !(Maybe SpanID)

  The ID of the generated span, otherwise the ID will be auto-generated.

• builderReferences :: !(Set Reference)

  Span references.

• builderTags :: !(Map Key Value)

  Initial set of tags.

• builderBaggages :: !(Map Key ByteString)

  Span context baggages.

• builderSampling :: !(Maybe Sampling)

  How the span should be sampled. If unset, the active's span sampling will be used if present, otherwise the span will not be sampled.

Instances

Show Builder

Defined in Control.Monad.Trace.Class

Methods

showsPrec :: Int -> Builder -> ShowS

show :: Builder -> String

showList :: [Builder] -> ShowS

IsString Builder

Defined in Control.Monad.Trace.Class

Methods

fromString :: String -> Builder

type Name = Text

The name of a span.

builder :: Name -> Builder

Returns a Builder with the given input as name and all other fields empty.

data Sampling

A trace sampling strategy.

Instances

Eq Sampling

Defined in Control.Monad.Trace.Internal

Methods

(==) :: Sampling -> Sampling -> Bool

(/=) :: Sampling -> Sampling -> Bool

Show Sampling

Defined in Control.Monad.Trace.Internal

Methods

showsPrec :: Int -> Sampling -> ShowS

show :: Sampling -> String

showList :: [Sampling] -> ShowS

alwaysSampled :: Sampling

Returns a Sampling which always samples.

neverSampled :: Sampling

Returns a Sampling which never samples.

sampledEvery :: Int -> Sampling

Returns a Sampling which randomly samples one in every n spans.

sampledWhen :: Bool -> Sampling

Returns a Sampling which samples a span iff the input is True.

debugEnabled :: Sampling

Returns a debug Sampling. Debug spans are always sampled.

Annotating spans

type Key = Text

The type of annotations' keys.

Keys starting with double underscores are reserved and should not be used.

data Value

Metadata attached to a span.

tagDoubleValue :: Double -> Value

Generates a tag value from a double.

tagInt64Value :: Integral a => a -> Value

Generates a 64-bit integer tag value from any integer.

tagTextValue :: Text -> Value

Generates a Unicode text tag value.

logValue :: ToJSON a => a -> Value

Generates a log value with the time of writing as timestamp. Note that the value may be written later than it is created. For more control on the timestamp, use logValueAt.

logValueAt :: ToJSON a => POSIXTime -> a -> Value

Generates a log value with a custom time.