From 890e6df09884277f9fcd5fd6b706091a2e23e6ea Mon Sep 17 00:00:00 2001
From: Rob Rix <rob.rix@me.com>
Date: Mon, 30 Apr 2018 17:07:01 -0400
Subject: [PATCH] Ranges and Spans have lower bounds.

---
 src/Data/Range.hs | 6 +++++-
 src/Data/Span.hs  | 6 +++++-
 2 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/src/Data/Range.hs b/src/Data/Range.hs
index 280303b77..51f9048f4 100644
--- a/src/Data/Range.hs
+++ b/src/Data/Range.hs
@@ -7,9 +7,10 @@ module Data.Range
 , subtractRange
 ) where
 
-import Prologue
 import Data.Aeson
 import Data.JSON.Fields
+import Data.Semilattice.Lower
+import Prologue
 
 -- | A half-open interval of integers, defined by start & end indices.
 data Range = Range { start :: {-# UNPACK #-} !Int, end :: {-# UNPACK #-} !Int }
@@ -51,3 +52,6 @@ instance Ord Range where
 
 instance ToJSONFields Range where
   toJSONFields Range{..} = ["sourceRange" .= [ start, end ]]
+
+instance Lower Range where
+  lowerBound = Range 0 0
diff --git a/src/Data/Span.hs b/src/Data/Span.hs
index aaef4c9ad..cd1a7a928 100644
--- a/src/Data/Span.hs
+++ b/src/Data/Span.hs
@@ -9,10 +9,11 @@ module Data.Span
 , emptySpan
 ) where
 
-import Prologue
 import Data.Aeson ((.=), (.:))
 import qualified Data.Aeson as A
 import Data.JSON.Fields
+import Data.Semilattice.Lower
+import Prologue
 
 -- | Source position information
 data Pos = Pos
@@ -56,3 +57,6 @@ instance A.FromJSON Span where
 
 instance ToJSONFields Span where
   toJSONFields sourceSpan = [ "sourceSpan" .= sourceSpan ]
+
+instance Lower Span where
+  lowerBound = Span (Pos 1 1) (Pos 1 1)