From 92011e8ef25eb8326eb41e6e59b99a45434b528b Mon Sep 17 00:00:00 2001
From: Rob Rix <rob.rix@me.com>
Date: Fri, 30 Mar 2018 18:45:48 -0400
Subject: [PATCH] Define a variable convenience.

---
 src/Data/Abstract/Evaluatable.hs | 4 ++++
 src/Data/Syntax.hs               | 2 +-
 2 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/src/Data/Abstract/Evaluatable.hs b/src/Data/Abstract/Evaluatable.hs
index ecd1a8178..70e57763e 100644
--- a/src/Data/Abstract/Evaluatable.hs
+++ b/src/Data/Abstract/Evaluatable.hs
@@ -6,6 +6,7 @@ module Data.Abstract.Evaluatable
 , Unspecialized(..)
 , LoadError(..)
 , EvalError(..)
+, variable
 , evaluateTerm
 , evaluateModule
 , evaluatePackage
@@ -65,6 +66,9 @@ data EvalError value resume where
   -- Indicates we weren't able to dereference a name from the evaluated environment.
   FreeVariableError :: Name -> EvalError value value
 
+variable :: MonadEvaluatable location term value m => Name -> m value
+variable name = lookupWith deref name >>= maybeM (throwException (FreeVariableError name))
+
 deriving instance Eq (EvalError a b)
 deriving instance Show (EvalError a b)
 instance Show1 (EvalError value) where
diff --git a/src/Data/Syntax.hs b/src/Data/Syntax.hs
index a20424f92..6415e8ca7 100644
--- a/src/Data/Syntax.hs
+++ b/src/Data/Syntax.hs
@@ -106,7 +106,7 @@ instance Ord1 Identifier where liftCompare = genericLiftCompare
 instance Show1 Identifier where liftShowsPrec = genericLiftShowsPrec
 
 instance Evaluatable Identifier where
-  eval (Identifier name) = lookupWith deref name >>= maybeM (throwException (FreeVariableError name))
+  eval (Identifier name) = variable name
 
 instance FreeVariables1 Identifier where
   liftFreeVariables _ (Identifier x) = pure x