(comment mostly for entertainment) The announcement of the Haskell error index conjured memories of the Fortran I stop book. On an error, the original Fortran compiler executed a halt instruction. To find the cause, one would read the memory address of the halt from the console lights and manually look the address up in the stop book, a thick 11"x17" computer printout. In the Haskell error index, the codes are permanent identifiers for evolving diagnostic explanations. In contrast, Fortran stop numbers varied with compiler version, while the explanations were essentially static. The stop book was indispensable, but far from user-friendly. If reasonably curated, the error index could be a big advance in the latter respect. Doug McIlroy