Matthias, My apologies for being deliberately obtuse. Of course, I understood what you were saying, but my point is this: The name of the monadic "return" combinator is perfectly sensible to anyone who understands the continuation semantics of imperative languages. While it shouldn't be necessary to be a denotational semanticist to program in Haskell, I think it is essential to appreciate the philosophical difference between the _being_ of functional programming and the _doing_ of imperative programming, if you're going to play with something like the I/O monad in Haskell. If you don't grasp that when you construct a monad, you're creating a value that represents an action, or in other words have a basic understanding of the functional denotation of an imperative command, you don't really understand what you're "doing" with monads, and your program is likely not to compute what you intend. In this sense, maybe it's better not to change the (initially) confusing "return" name, but to regard it as a pons asinorum that the student must cross. Cheers, --Joe On 16-Feb-2001 Matthias Felleisen wrote:
From: jhf@lanl.gov X-Priority: 3 (Normal) Content-Type: text/plain; charset=us-ascii Date: Fri, 16 Feb 2001 16:53:13 -0700 (MST) Organization: Los Alamos National Laboratory Cc: karczma@info.unicaen.fr, haskell-cafe@haskell.org
On 16-Feb-2001 Matthias Felleisen wrote:
Because imperative languages have named one half of the denotation (the value return) and not all of it for a long long long time. It's too late for Haskell to change that. -- Matthias
Well now, if I am to understand what a return statement in C does, I must realize not only that it may return a value to a calling routine, but also that it preserves the store. If it allowed the store to vanish, it wouldn't be very useful, would it? So I don't see how it's reasonable to assert that "return" means only one of these two things to a C programmer.
Cheers, --Joe
Let me spell it out in detail. When a C programmer thinks about the 'return' type of a C function, he thinks about the value-return half of a return statement's denotation. The other half, the modified store, remains entirely implicit as far as types are concerned. This is what Jerzy's exam question was all about.
-- Matthias
Joseph H. Fasel, Ph.D. email: jhf@lanl.gov Technology Modeling and Analysis phone: +1 505 667 7158 University of California fax: +1 505 667 2960 Los Alamos National Laboratory post: TSA-7 MS F609; Los Alamos, NM 87545