I think my initial question didn't capture the intent.... and my attempt to simplify the function did exactly the opposite... so i will try again, this time not being lazy, and defining more :)
; Time is initialized at 30 min (x).
; Check each element in a string containing either "A"s or "B"s;
; if "A" add "v" minute(s) to x, if "B" subtract "v" minute(s) from x (let's call this value "xi");
; Upon each check for A or B re-initialize x to be the current xi value multiplied by 2 (This way the next check ; can use the new x for it's increase/decrease)
; Use these 4 calls to validate function works correctly:
; (ugh "AAAA" 1) = 255
; (ugh "BBBB" 1) = 225
; (ugh "ABAB" 2) = 250
My original-like solution using "Sets" which work:
* I changed to get rid of trunc, and make easier to read and align to the specs above.
(def ugh (str v)
(set x 15)
(for i 0 (- (len str) 1) (set xi (* x 2))
(if (is "A" (cut str i (+ i 1)))
(set x (+ xi v))
(set x (- xi v))i))x)
Note: Although I set x to 15, notice the "set xi" was placed to bump that to 30 on the first pass.
As pointed out I tried unsuccessfully to remove the "sets". drcode and skenney26 both suggested ideas which do not work (not to their fault rather it was my laziness in asking the question properly). I re-worked the suggested solution to present the spirit of the intended function using the new specs above.
(def ugh (str v)
(let x 15
(on c str
(let xi (* x 2)
(if (is c #\A)
(++ x (+ xi v))
(-- x (- xi v)))))
x))
As stated this does not work. Sorry drcode... I didn't try the pure functional version - it looked more complicated than I wanted to go.
My solution after looking hacking with suggestions for ideas:
(def ugh (str v)
(let x 15
(on c str
(++ x (sub-ugh x v str index)))x))
(def sub-ugh (x v str i)
(if (is "A" (cut str i (+ i 1)))
(++ x v)
(-- x v)))
Now, call me silly but does't this seem like overly complicated code compared to a relatively simple problem ?
not just complicted from an amount of work perspective, but from a code readability perspective too ?
Why wouldn't the ARChitects of LISP or ARC make a set like function that is global within a function ?
Doesn't this seem like a smart thing to do ? Is this against the spirit of lisp/arc/scheme ?
Thanks for stickin with me on this overly verbose newbie problem.
T.
By the sound of things, the problem is that the variables created by one function are being modified by other functions. In that case, the solution is to use local variables instead of global variables. To do that, you just need to wrap the function body in a single let form:
(def ugh (str v)
(let x 15
(for i 0 (- (len str) 1) (set xi (* x 2))
(if (is "A" (cut str i (+ i 1)))
(set x (+ xi v))
(set x (- xi v)) i)) x))
The sets will refer to the locally created variable, not a global variable.
(= x 100000)
=> 100000
(ugh "AAAA" 1)
=> 255
x
=> 100000
The global x has not been modified, because the function created a local x variable and used that instead.
Here's a more concise version of that function:
(def ugh (str v)
(let x 15
(on c str
(= x (* x 2))
(if (is #\A c) (++ x v)
(-- x v)))
x))
and here's a version that uses no sets at all:
(def ugh (str v (o x 15))
(let x2 (* 2 x)
(if (is "" str) x
(is #\A str.0) (ugh (cut str 1) v (+ x2 v))
(ugh (cut str 1) v (- x2 v)))))
ah! I see. my rudimentary tests for (= x(...)) and probably having x set from previous iterations of code led me to believe (= x(...)) always changed the global x.
