In multiple languages (perl, haskell), I find myself writing a function that runs a system command and returns False (or sometimes, throws an exception) if it f

In multiple languages (perl, haskell), I find myself writing a function that runs a system command and returns False (or sometimes, throws an exception) if it failed nonzero. Also, in haskell I use these frequently to have monadic versions of some common flow control functions (some nonstandard libraries have similar functions to these but it's easier to write my own): whenM c a = c >>= flip when a unlessM c a = c >>= flip unless a (>>?) = whenM (>>!) = unlessM -- low fixity allows eg, foo bar >>! error $ "failed " ++ meep infixr 0 >>? infixr 0 >>!