Yep. Robby
On Tue, Dec 21, 2010 at 11:11 PM, Sayth Renshaw <[email protected]> wrote: > > > On Wed, Dec 22, 2010 at 2:04 PM, Robby Findler <[email protected]> > wrote: >> >> FWIW, if you were in my class, that solution would get few points. You >> may have noticed people asking you about the design recipe in this >> thread. That is a reference to this book that you might find useful: >> >> http://www.htdp.org/ >> >> Robby >> >> On Tue, Dec 21, 2010 at 8:49 PM, Sayth Renshaw <[email protected]> >> wrote: >> > >> > >> > On Wed, Dec 22, 2010 at 1:19 PM, Sayth Renshaw <[email protected]> >> > wrote: >> >> >> >> >> >> On Wed, Dec 22, 2010 at 1:02 PM, Danny Yoo <[email protected]> wrote: >> >>> >> >>> >> (define (netpay gross tax-rate) >> >>> >> (-(gross)(* gross tax-rate))) >> >>> >> >> >>> >> So I expect the function to calculate as >> >>> >> >> >>> >> = (-(240)(* 240 0.15) >> >>> >> = ( - 240 36) >> >>> >> = 204 >> >>> >> >>> >> >>> Just to be more careful: when you're showing the calculation, make >> >>> sure to include the use of the function: >> >>> >> >>> (netpay 240 0.15) >> >>> = (-(240)(* 240 0.15) >> >>> = ( - 240 36) >> >>> = 204 >> >>> >> >>> >> >>> There's a hitch on the first step in the calculation, and it has to do >> >>> with the parens. Unlike its use in traditional math notation, parens >> >>> are significant in this language: that is, every use of paren has to >> >>> mean something: it's not superfluous: if you have too many or too few, >> >>> it changes the meaning of the program. >> >>> >> >>> >> >>> So, within the larger term here: >> >>> >> >>> (- (240) (* 240 0.15)) >> >>> >> >>> the subterm >> >>> >> >>> (240) >> >>> >> >>> means "call the function 240". That may not be what you intend, but >> >>> that what it means in this language. >> >>> >> >>> >> >>> You can see this if you go back to what the error message is saying: >> >>> >> >>> function call: expected a defined function name or a primitive >> >>> operation name after an open parenthesis, but found a function >> >>> argument name >> >>> >> >>> It's basically trying to point out this problem, that the use of >> >>> "(gross)" within the expression >> >>> >> >>> (-(gross)(* gross tax-rate)) >> >>> >> >>> is trying to use gross as if it were a function, rather than the >> >>> numeric argument to netpay. >> >> >> >> the subterm >> >> >> >> (240) >> >> >> >> means "call the function 240". That may not be what you intend, but >> >> that what it means in this language. >> >> >> >> Awesome pickup, thank you. Can I ask how I could then specify gross a >> >> single item in the formula and not as a function? >> > >> > Thank you everyone, I have solved it and thank you for picking me up on >> > the >> > small intricises. >> > >> > This is my solution though it works I do feel I "Cheated" somewhat but >> > this >> > is what I have done and tested working. >> > >> > (define tax-rate 0.15) >> > (define pay-rate 12) >> > (define (gross hours) >> > (* hours pay-rate)) >> > >> > (define (netpay gross tax-rate) >> > (- gross 0 (* gross tax-rate))) >> > >> > >> >> (netpay (gross 20)tax-rate) >> > 204 >> >> >> > >> > Sayth >> > >> > _________________________________________________ >> > For list-related administrative tasks: >> > http://lists.racket-lang.org/listinfo/users >> > > > Indeed I know what you are referencing. > > ;; Contract: area-of-ring : number number -> number > > > ;; Purpose: to compute the area of a ring whose radius is > ;; outer and whose hole has a radius of inner > > > ;; Example: (area-of-ring 5 3) should produce 50.24 > > ;; Definition: [refines the header] > > (define (area-of-ring outer inner) > (- (area-of-disk outer) > > (area-of-disk inner))) > > ;; Tests: > (area-of-ring 5 3) > > ;; expected value > 50.24 > > _________________________________________________ For list-related administrative tasks: http://lists.racket-lang.org/listinfo/users
