gab_kmさんは関数だったらしい

gab_km.hs

type Tuna = String
type Tea = String
type Ginger = String

gab_km :: Tuna -> Tea -> Ginger
gab_km "中トロ" "緑茶" = "ガリ"
gab_km "中トロ" _      = "緑茶よこせ"
gab_km _        "緑茶" = "中トロよこせ"
gab_km _        _      = "こんなもん喰えるか！"

やってみた

$ ghci
GHCi, version 7.4.2: http://www.haskell.org/ghc/  :? for help
Loading package ghc-prim ... linking ... done.
Loading package integer-gmp ... linking ... done.
Loading package base ... linking ... done.
Prelude> :load gab_km.hs 
[1 of 1] Compiling Main             ( gab_km.hs, interpreted )
Ok, modules loaded: Main.
*Main> 
*Main> putStrLn $ gab_km "中トロ" "緑茶"
ガリ
*Main> putStrLn $ gab_km "カッパ巻き" "緑茶"
中トロよこせ
*Main> putStrLn $ gab_km "ピザ" "コーラ"
こんなもん喰えるか！