Hello. Today I wrote a small program to experiment with the Applicative class. The program is supposed to use an "applicative reader", similar to a "monad reader", to evaluate arithmetic expressions. But when compiling the program with ghc-7.6.1, I get the following message: $ ghc --make applicative-eval [1 of 1] Compiling Main ( applicative-eval.hs, applicative-eval.o ) ghc: panic! (the 'impossible' happened) (GHC version 7.6.1 for x86_64-unknown-linux): expectJust cpeBody:collect_args Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug If the line eval (Let s a b) = \m -> eval b ((s,eval a m):m) is commented out, the program compiles without problems. Is this a known issue with the compiler? The source code is attached. Romildo