Fix bug with observeAndSample function from Histogram

CHANGELOG.md

@@ -0,0 +1,8 @@
+
+## 2.3.0
+
+*   Change the `observeAndSample` function from the
+    `System.Metrics.Prometheus.Metric.Histogram` module to return the value of
+    the sample that was just added, instead of the previous sample.
+    This change matches similar functions for `Counter`s and `Gauge`s.
+    [#51](https://github.com/bitnomial/prometheus/pull/51)

prometheus.cabal

@@ -1,13 +1,13 @@
 name:                prometheus
-version:             2.2.4
+version:             2.3.0
 synopsis:            Prometheus Haskell Client
 homepage:            http://github.com/bitnomial/prometheus
 bug-reports:         http://github.com/bitnomial/prometheus/issues
 license:             BSD3
 license-file:        LICENSE
 author:              Luke Hoersten
 maintainer:          luke@bitnomial.com, opensource@bitnomial.com
-copyright:           Bitnomial, Inc. (c) 2016-2019
+copyright:           Bitnomial, Inc. (c) 2016-2023
 category:            Metrics, Monitoring, Web, System
 build-type:          Simple
 cabal-version:       >=1.10

src/System/Metrics/Prometheus/Metric/Counter.hs

@@ -9,13 +9,13 @@
     set,
 ) where
 
 import Control.Applicative ((<$>))
 import Control.Monad (when)
 import Data.Atomics.Counter (AtomicCounter, incrCounter, newCounter, writeCounter)
 
 
 newtype Counter = Counter {unCounter :: AtomicCounter}
-newtype CounterSample = CounterSample {unCounterSample :: Int}
+newtype CounterSample = CounterSample {unCounterSample :: Int} deriving Show
 
 
 new :: IO Counter

src/System/Metrics/Prometheus/Metric/Gauge.hs

@@ -11,12 +11,12 @@
     modifyAndSample,
 ) where
 
 import Control.Applicative ((<$>))
 import Data.IORef (IORef, atomicModifyIORef', newIORef)
 
 
 newtype Gauge = Gauge {unGauge :: IORef Double}
-newtype GaugeSample = GaugeSample {unGaugeSample :: Double}
+newtype GaugeSample = GaugeSample {unGaugeSample :: Double} deriving Show
 
 
 new :: IO Gauge

src/System/Metrics/Prometheus/Metric/Histogram.hs

@@ -11,7 +11,7 @@
     observeAndSample,
 ) where
 
 import Control.Applicative ((<$>))
 import Control.Monad (void)
 import Data.Bool (bool)
 import Data.IORef (
@@ -36,6 +36,7 @@
     , histSum :: !Double
     , histCount :: !Int
     }
+    deriving Show
 
 
 new :: [UpperBound] -> IO Histogram
@@ -49,7 +50,7 @@
 observeAndSample :: Double -> Histogram -> IO HistogramSample
 observeAndSample x = flip atomicModifyIORef' update . unHistogram
   where
-    update histData = (hist' histData, histData)
+    update histData = (hist' histData, hist' histData)
     hist' histData =
         histData
             { histBuckets = updateBuckets x $ histBuckets histData

src/System/Metrics/Prometheus/Metric/Summary.hs

@@ -8,3 +8,4 @@ data SummarySample = SummarySample
     , sumSum :: !Int
     , sumCount :: !Int
     }
+    deriving Show