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
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