From f74dd82111c0f50fc7b1a222c796d258e82281fb Mon Sep 17 00:00:00 2001
From: Camil Staps
Date: Wed, 22 Nov 2017 11:19:41 +0100
Subject: Resolve run-time error for functions that use arguments twice further
 down the expression graph

---
 pf.icl   | 12 ++++++------
 test.sh  |  2 +-
 test.tsv |  1 +
 3 files changed, 8 insertions(+), 7 deletions(-)

diff --git a/pf.icl b/pf.icl
index 7e0f76f..46016e1 100644
--- a/pf.icl
+++ b/pf.icl
@@ -134,20 +134,20 @@ optim (Lambda id e)
 | otherwise = Ident "const" @ optim e
 where
 	optApp :: Expr -> Expr
-	optApp (f @ x)
-	| hasIdent id f && hasIdent id x = Ident "ap" @ Lambda id f @ Lambda id x
-	| otherwise = case moveOutside id (f @ x) of
+	optApp (f @ x) = case moveOutside id (f @ x) of
 		a=:(f @ Ident id`) -> if (id == id`) f (Ident "const" @ a)
 		a                  -> Ident "const" @ a
-optim (Ident "flip" @ Ident "ap" @ Ident "id") = Ident "join"
-optim (f @ x) = optim f @ optim x
+optim (f @ x) = case optim f @ optim x of
+	Ident "flip" @ Ident "ap" @ Ident "id" -> Ident "join"
+	Ident "ap" @ f @ Ident "id" -> Ident "join" @ f
+	e -> e
 optim e = e
 
 moveOutside :: Ident Expr -> Expr
 moveOutside _ (Ident id) = Ident id
 moveOutside _ (Literal l) = Literal l
 moveOutside id (f @ x)
-| hasIdent id f && hasIdent id x = abort "moveOutside on @ with id in both sides"
+| hasIdent id f && hasIdent id x = Ident "ap" @ Lambda id f @ Lambda id x @ Ident id
 | hasIdent id f = case moveOutside id f of
 	Ident id -> Ident "flip" @ Ident "id" @ x @ Ident id
 	g @ Ident id -> Ident "flip" @ g @ x @ Ident id
diff --git a/test.sh b/test.sh
index cc6a14b..66ffe88 100755
--- a/test.sh
+++ b/test.sh
@@ -4,7 +4,7 @@ SUCCESS=true
 while IFS=$'\t' read -r req res; do
 	outcome="$(./pf -nt "$req" | grep Result | cut -d' ' -f3-)"
 	if [ "$res" != "$outcome" ]; then
-		echo "Test failed: $req"
+		echo "Test failed:     $req"
 		echo "Expected result: $res"
 		echo "Actual result:   $outcome"
 		SUCCESS=false
diff --git a/test.tsv b/test.tsv
index bc25a74..e4e7840 100644
--- a/test.tsv
+++ b/test.tsv
@@ -13,3 +13,4 @@
 \x y -> y 10	const (flip id 10)
 \f a b c d -> f b c d a	(o) flip ((o) ((o) flip) ((o) ((o) flip)))
 \f x -> f x x	join
+\f -> f f 10	flip (join id) 10
-- 
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