Re: [Haskell-cafe] Sequencing Operations in a Monad

Unfortunately if I wrap my matrix references in the IO monad, then at best computations like S = A + B are themselves IO computations and thus whenever they are 'invoked' the computation ends up getting performed repeatedly contrary to my intentions. This sounds like a case for the infamous performUnsafeIO. The reason

SevenThunders wrote: this is "unsafe" is that the compiler assumes that the IO computation it wraps has no visible side effects, so it doesn't matter when it is performed or how many times it gets performed. If your IO computation indeed has this nature then you are OK, but its up to you to make sure of this. Paul.