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#lang typed/racket/base
(provide (all-defined-out))
;; Returns the interpolated distance of z from za toward zb
;; Examples: if z = za, this returns 0.0
;; if z = zb, this returns 1.0
;; if z = (za + zb) / 2, this returns 0.5
;; Intuitively, regard a use (solve-t z za zb) as "the point between za and zb".
(define-syntax-rule (solve-t z za zb)
(/ (- z za) (- zb za)))
(define-syntax-rule (unsolve-t za zb t)
(cond [(eq? t 0) za]
[(eq? t 1) zb]
[else (+ (* t zb) (* (- 1 t) za))]))
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