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Andrew Wilcox wrote: > From the responses so far, > (exact? "a string") > appears to be immediately confusing to most people. Well, it is always #t. But: (exact? (expression yielding string result)) may not be, if the expression uses inexact operations. Sorry I haven't been following the (rather long, detailed) discussion here, but I would love to see this proposal in effect. It's important that people be able to express the inexactness of their calculations - regardless of the type of the result. Among other things it would be desirable from a program verification standpoint. If I have a test suite that claims that a test passes but in reality it is dependent on the actual values of operands of inexact operations, I would really want to know that. Which arises from a (possibly even stranger, but possibly more clear) expression: (exact? (expression yielding boolean)) possibly yielding (exactly!) #f There was a language called Numeric Turing in the 80's that had similar ideas, although not carried as far. It was oriented to proofs of correctness, including the degree of exactness of results. I also do similar things with probabilistic execution of programs - conditionals return 'maybe' values with probability distributions associated with them. ../Dave