Add a pprTraceWith functionwip/ppr-trace-with

1 files changed, 9 insertions, 3 deletions

diff --git a/compiler/utils/Outputable.hs b/compiler/utils/Outputable.hs
index fee257d98a..47b0d67449 100644
--- a/compiler/utils/Outputable.hs
+++ b/compiler/utils/Outputable.hs
@@ -81,8 +81,8 @@ module Outputable (
 
         -- * Error handling and debugging utilities
         pprPanic, pprSorry, assertPprPanic, pprPgmError,
-        pprTrace, pprTraceDebug, pprTraceIt, warnPprTrace, pprSTrace,
-        pprTraceException, pprTraceM,
+        pprTrace, pprTraceDebug, pprTraceWith, pprTraceIt, warnPprTrace,
+        pprSTrace, pprTraceException, pprTraceM,
         trace, pgmError, panic, sorry, assertPanic,
         pprDebugAndThen, callStackDoc,
     ) where
@@ -1196,9 +1196,15 @@ pprTrace str doc x
 pprTraceM :: Applicative f => String -> SDoc -> f ()
 pprTraceM str doc = pprTrace str doc (pure ())
 
+-- | @pprTraceWith desc f x@ is equivalent to @pprTrace desc (f x) x@.
+-- This allows you to print details from the returned value as well as from
+-- ambient variables.
+pprTraceWith :: Outputable a => String -> (a -> SDoc) -> a -> a
+pprTraceWith desc f x = pprTrace desc (f x) x
+
 -- | @pprTraceIt desc x@ is equivalent to @pprTrace desc (ppr x) x@
 pprTraceIt :: Outputable a => String -> a -> a
-pprTraceIt desc x = pprTrace desc (ppr x) x
+pprTraceIt desc x = pprTraceWith desc ppr x
 
 -- | @pprTraceException desc x action@ runs action, printing a message
 -- if it throws an exception.