X-Git-Url: http://lambda.jimpryor.net/git/gitweb.cgi?p=lambda.git;a=blobdiff_plain;f=damn.mdwn;h=ad6877528976c79ede34ee1cd1d6c1d182e9e330;hp=9524086ab9dfb1b3c0ec56a4b732a8680a38359f;hb=bdf5f58fbd0655365f8440f77c481846ffc60ee9;hpb=2664d5fe30e878c4c6fb6f6ef7549dea0bf03582 diff --git a/damn.mdwn b/damn.mdwn index 9524086a..ad687752 100644 --- a/damn.mdwn +++ b/damn.mdwn @@ -1,3 +1,20 @@ +1. Sentences have truth conditions. + +2. If "John read the book" is true, then it follows that: + John read something, + Someone read the book, + John did something to the book, + etc. + +3. If "John read the damn book", + all the same entailments follow. + To a first approximation, "damn" does not affect at-issue truth + conditions. + +4. "Damn" does contribute information about the attitude of the speaker + towards some aspect of the situation described by the sentence. + + Expressives such as "damn" have side effects that don't affect the at-issue value of the sentence in which they occur. What this claim says is unpacked at some length here: . @@ -43,7 +60,7 @@ What's going on here? --------------------- `(cons M N)` is a request to build an ordered pair out of the values M and N. -Scheme displays that pair as `'(M . N)` You can't write `(M . N)` yourself and expect Scheme to understand that you're talking about this pair. If you tried, to, Scheme would think you're trying to apply the function M to some arguments, which you're not, and also +Scheme displays that pair as `'(M . N)` You can't write `(M . N)` yourself and expect Scheme to understand that you're talking about this pair. If you tried to, Scheme would think you're trying to apply the function M to some arguments, which you're not, and also Scheme would be confused by what argument the `.` is supposed to be. So, you say: (cons M N) @@ -56,7 +73,7 @@ You *can* write `'(M . N)` (with the prefixed single quote), and Scheme will und There is an underlying reason why parentheses are used both when displaying the ordered pair, and also to mean "apply this function to these arguments." However, at this point, you may well see this as a confusing overloading of parentheses to fill different syntactic roles. -Now what about the elements of our ordered pairs. Why do we say `(cons 'the 'man)`. Why are those single quotes there? Well, if you just said `(cons the man)`, Scheme would understand `the` and `man` to be variables, and it would complain that you hadn't bound these variables to any values. We don't want to build an ordered pair out of the values possessed by variables `the` and `man`. Instead, we want to just make up some primitive value THE to stand for the meaning of an object-language determiner, and some primitive value MAN to stand for the meaning of an object-language noun phrase. The notation `'the` is Scheme's way of designating a primitive atomic value. Note there is no closing single quote, only a prefixed one. Scheme calls these primitive atomic values "symbols." That term is a bit misleading, because the symbol `'the` is not the same as the variable `the`. Neither is it the same as what's called the string `"the"`. The latter is a structured value, composed out of three character values. The symbol `'the`, on the other hand, is an atomic value. It has no parts. (The notation the programmer uses to designate this atomic value has four characters, but the value designated itself has no parts.) If you think this is all somewhat confusing, you're right. It gets easier with practice. +Now what about the elements of our ordered pairs. Why do we say `(cons 'the 'man)`. Why are those single quotes there? Well, if you just said `(cons the man)`, Scheme would understand `the` and `man` to be variables, and it would complain that you hadn't bound these variables to any values. We don't want to build an ordered pair out of the values possessed by variables `the` and `man`. Instead, we want to just make up some primitive value THE to stand for the meaning of an object-language determiner, and some primitive value MAN to stand for the meaning of an object-language noun. The notation `'the` is Scheme's way of designating a primitive atomic value. Note there is no closing single quote, only a prefixed one. Scheme calls these primitive atomic values "symbols." That term is a bit misleading, because the symbol `'the` is not the same as the variable `the`. Neither is it the same as what's called the string `"the"`. The latter is a structured value, composed out of three character values. The symbol `'the`, on the other hand, is an atomic value. It has no parts. (The notation the programmer uses to designate this atomic value has four characters, but the value designated itself has no parts.) If you think this is all somewhat confusing, you're right. It gets easier with practice. `'the` can also be written `(quote the)`. This is even more confusing, because here the `the` is not interpreted as a variable. (Try `(let* ((the 3)) (quote the))`.) If you come across `(quote the)`, just read it as a verbose (and perhaps misleading) way of writing `'the`, not as the application of any function to any value. @@ -248,12 +265,12 @@ It's not immediately clear how to do it with "undelimited" continuations, of the (define damn (lambda () (call/cc (lambda (k) (cons (cons 'side-effect 'bad) (k 'id)))))) -The idea here is we capture the continuation that `(damn)` has when it gets evaluated. This continuation is bound to the variable `k`. We supply `'id` as an argument to that continuation. When the main, at-issue tree is all built, then we return a pair `'((side-effect . bad) AT-ISSUE-TREE)`. +The idea here is we capture the continuation that `(damn)` has when it gets evaluated. This continuation is bound to the variable `k`. We supply `'id` as an argument to that continuation. When the main, at-issue tree is all built, then we return a pair `'((side-effect . bad) . AT-ISSUE-TREE)`. However, this doesn't work. The reason is that an undelimited continuation represents the future of the evaluation of `(damn)` *until the end of the computation*. So when `'id` is supplied to `k`, we go back to building the at-issue tree until we're finished *and that's the end of the computation*. We never get to go back and evaluate the application of `(cons (cons 'side-effect 'bad) <>)` to anything. -With undelimited continuations +With delimited continuations ------------------------------ The straightforward way to fix this is to use, not undelimited continuations, but instead a more powerful apparatus called "delimited continuations." These too will be explained in due course, don't expect to understand all this now. @@ -299,7 +316,7 @@ Now to pair that with an affective side-issue content, we'd instead define `damn (define damn (lambda () (shift k (cons (cons 'side-effect 'bad) (k 'id))))) -And voila: +And voilà! (reset (cons (cons 'the 'man) (cons 'read @@ -329,94 +346,7 @@ Ken Shan pointed out a lovely way to get to the same end-point still using only (lambda () 'id))))))))) (let ((assert (car pragma)) ; this binds assert to the first element of the pair pragma (damn (cdr pragma))) ; this binds damn to the second element of the pair pragma - (assert (cons (cons 'the 'student) (cons 'read (cons 'the (cons (damn) 'book))))))) - -We won't do much to explain this. We'll just leave it for you to chew on. - - - - - #lang racket - ;(define damn (lambda () 'id)) - (define damn (lambda () (call/cc (lambda (k) - ; (k 'id) - (print "Something's bad") - (k 'id) - )))) - - (list (list 'the (list (damn) 'man)) - (list 'read - (list 'the (list (damn) 'book)))) - - - - - - #lang racket - (require racket/control) - - (define damn0 (lambda () - 'id)) - - (define damn1 (lambda () - (cons '("side effect" bad) - 'id))) - - (define damn2 (lambda () (shift k - (cons '("side effect" bad) - (list (k 'id)))))) - - (define damn3 (lambda () (shift k - (list (k 'id) - '("side effect" bad))))) - - -; Now if we use damn0, our compositional semantics will work OK but -; we don't yet have any affective contribution: - - (list "main content" 'i (list 'like (list 'the (damn0) 'boy))) - ; '("main content" i (like (the id boy))) - - -; If we use damn1, we've added in the affective side effect: - - (list "main content" 'i (list 'like (list 'the (damn1) 'boy))) - ; '("main content" i (like (the (("side effect" bad) . id) boy))) - -; However, the context (list 'the <> 'boy) is now being asked to operate -; on an element (("side effect" bad) . id), and it may complain it doesn't -; know what that is. It knows how to use 'id to get (list 'the 'id 'boy), -; and how to use 'bad to get (list 'the 'bad 'boy), but we're supposed to -; have something different here. - -; To get what we want we need to use (delimited) continuations: - (reset (list "main content" 'i (list 'like (list 'the (damn2) 'boy)))) - ; '(("side effect" bad) ("main content" i (like (the id boy)))) - -; or to get the side effect at the end: - - (reset (list "main content" 'i (list 'like (list 'the (damn3) 'boy)))) - ; '(("main content" i (like (the id boy))) ("side effect" bad)) - -; If you're working in the interactive interpreter, the outermost "reset" here -; is already in its default position, so it doesn't need to be explicitly -; specified: - - (list "main content" 'i (list 'like (list 'the (damn2) 'boy))) - ; '(("side effect" bad) ("main content" i (like (the id boy)))) - -; However, if you're executing this as a file, you would need to include explicit resets. - - - -; Instead of using reset/shift you could use an element like "print" in -; building the side effect, as we did in class. Here you wouldn't require an -; explicit continuation, but as Chris said, that's because "print" already -; represents an implicit continuation. - - (define damn4 (lambda () (begin (print "bad") 'id))) - (list "main content" 'i (list 'like (list 'the (damn4) 'boy))) - ; "bad"'("main content" i (like (the id boy))) -; + (assert (cons (cons 'the 'man) (cons 'read (cons 'the (cons (damn) 'book))))))) +We won't do much to explain this. We'll just leave it for you to digest, perhaps later in the course. When you succeed in doing so, you will be as delighted by it as we are.