update

Task/Safe-addition/Racket/safe-addition.rkt

@@ -0,0 +1,27 @@
+#lang racket
+
+;; 1. Racket has exact unlimited integers and fractions, which can be
+;;    used to perform exact operations.  For example, given an inexact
+;;    flonum, we can convert it to an exact fraction and work with that:
+(define (exact+ x y)
+  (+ (inexact->exact x) (inexact->exact y)))
+;; (A variant of this would be to keep all numbers exact, so the default
+;; operations never get to inexact numbers)
+
+;; 2. We can implement the required operation using a bunch of
+;;    functionality provided by the math library, for example, use
+;;    `flnext' and `flprev' to get the surrounding numbers for both
+;;    inputs and use them to produce the resulting interval:
+(require math)
+(define (interval+ x y)
+  (cons (+ (flprev x) (flprev y)) (+ (flnext x) (flnext y))))
+(interval+ 1.14 2000.0) ; -> '(2001.1399999999999 . 2001.1400000000003)
+;; (Note: I'm not a numeric expert in any way, so there must be room for
+;; improvement here...)
+
+;; 3. Yet another option is to use the math library's bigfloats, with an
+;;    arbitrary precision:
+(bf-precision 1024) ; 1024 bit floats
+;; add two numbers, specified as strings to avoid rounding of number
+;; literals
+(bf+ (bf "1.14") (bf "2000.0"))