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+{-# OPTIONS_GHC -O2 -fforce-recomp #-}
+{-# LANGUAGE BangPatterns #-}
+
+-- | This ticket is about demand `seq` puts its first argument under and
+-- how that affects call demands.
+module T18957 where
+
+-- | Should put its first argument under head demand
+seq' :: a -> b -> b
+seq' a b = seq a b
+{-# NOINLINE seq' #-}
+
+-- | The first argument is evaluated at once, but called every time it's
+-- evaluated
+g :: (Int -> Int) -> Int -> Int
+g f x = if x < 100 then f x else 200
+
+-- | The first argument is evaluated multiple times, but called at most once
+-- every time it's evaluated
+h1 :: (Int -> Int) -> Int -> Int
+-- Note that seq' is like seq, but NOINLINE. See h2 below why
+h1 f x = f `seq'` if x < 100 then f x else 200
+
+-- | Like h1, but using `seq` directly, which will rewrite the call site
+-- of @f@ to use the case binder instead, which means we won't evaluate it an
+-- additional time. So evaluated once and called once.
+h2 :: (Int -> Int) -> Int -> Int
+h2 f x = f `seq` if x < 100 then f x else 200
+
+h3 :: (Int -> Int) -> Int -> Int
+h3 f x = if x < 100 then f x + f (x+1) else 200