[plt-scheme] why local? (just curious)

Hi Sigrid --

Sequential assignment corresponds to a more traditional programming
style (let x = , let y = , ...) and sometimes it really is useful to
have the later assignment refer to the previous one.  For instance,

(let ([b^2 (square b)]
      [4ac (* 4 a c)]
      [b^2-4ac (- b^2 4ac)])
  ...)

Note how the third refers to the previous two.  These are NOT
*mutually* recursive: there is a strict ordering.

Shriram