From: Jim Pryor Date: Tue, 21 Dec 2010 03:24:02 +0000 (-0500) Subject: cps tweak X-Git-Url: http://lambda.jimpryor.net/git/gitweb.cgi?p=lambda.git;a=commitdiff_plain;h=745774e349b41deea78eab9163f64031016224bb cps tweak Signed-off-by: Jim Pryor --- diff --git a/cps_and_continuation_operators.mdwn b/cps_and_continuation_operators.mdwn index 2063ef0e..0d4eb1df 100644 --- a/cps_and_continuation_operators.mdwn +++ b/cps_and_continuation_operators.mdwn @@ -330,13 +330,14 @@ Next, try to figure out what this function does: [(null? l) (k 'notfound)] [(eq? (car l) a) (cdr l)] [(atom? (car l)) (cons (car l) (aux (cdr l) k))] - ; what happens when (car l) exists but isn't an atom? - [else (let ([car2 (let/cc k2 ; now what will happen when k2 is called? - (aux (car l) k2))]) - (cond - ; when will the following condition be met? what happens then? - [(eq? car2 'notfound) (cons (car l) (aux (cdr l) k))] - [else (cons car2 (cdr l))]))]))] + [else + ; what happens when (car l) exists but isn't an atom? + (let ([car2 (let/cc k2 ; now what will happen when k2 is called? + (aux (car l) k2))]) + (cond + ; when will the following condition be met? what happens then? + [(eq? car2 'notfound) (cons (car l) (aux (cdr l) k))] + [else (cons car2 (cdr l))]))]))] [lst2 (let/cc k1 ; now what will happen when k1 is called? (aux lst k1))]) (cond @@ -344,7 +345,6 @@ Next, try to figure out what this function does: [(eq? lst2 'notfound) lst] [else lst2])))) - Here is [the answer](/hints/cps_hint_3), but try to figure it out for yourself. Here is the hardest example. Try to figure out what this function does: diff --git a/hints/cps_hint_3.mdwn b/hints/cps_hint_3.mdwn index 845f5567..afc5beea 100644 --- a/hints/cps_hint_3.mdwn +++ b/hints/cps_hint_3.mdwn @@ -12,16 +12,17 @@ This function is developed in *The Seasoned Schemer* pp. 84-89. It accepts an at [(null? l) (k 'notfound)] [(eq? (car l) a) (cdr l)] [(atom? (car l)) (cons (car l) (aux (cdr l) k))] - ; when (car l) exists but isn't an atom, we try to remove a from (car l) - ; if we succeed we prepend the result to (cdr l) and stop - [else (let ([car2 (let/cc k2 - ; calling k2 with val will bind car2 to val and continue with the (cond ...) block below - (aux (car l) k2))]) - (cond - ; if a wasn't found in (car l) then prepend (car l) to the result of removing a from (cdr l) - [(eq? car2 'notfound) (cons (car l) (aux (cdr l) k))] - ; else a was found in (car l) - [else (cons car2 (cdr l))]))]))] + [else + ; when (car l) exists but isn't an atom, we try to remove a from (car l) + ; if we succeed we prepend the result to (cdr l) and stop + (let ([car2 (let/cc k2 + ; calling k2 with val will bind car2 to val and continue with the (cond ...) block below + (aux (car l) k2))]) + (cond + ; if a wasn't found in (car l) then prepend (car l) to the result of removing a from (cdr l) + [(eq? car2 'notfound) (cons (car l) (aux (cdr l) k))] + ; else a was found in (car l) + [else (cons car2 (cdr l))]))]))] [lst2 (let/cc k1 ; calling k1 with val will bind lst2 to val and continue with the (cond ...) block below (aux lst k1))])