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alexeevg / ipprint

Tiny helper for pretty-printing values in ghci console
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Round trip through the parser/prettyprinter can lose precision #1

Open orlitzky opened 11 years ago

orlitzky commented 11 years ago

I'm using the numbers package in GHCI, and the output precision can be truncated when it passes through the parser. An example (without ipprint):

Prelude> import Data.Number.BigFloat
Prelude Data.Number.BigFloat> 0 :: BigFloat Prec50
0.00000000000000000000000000000000000000000000000000e0

I think the problem is that we can use this output to assign to a non-big float. That is,

Prelude> let x = 0.123456789012345678901234567890e0
Prelude> x
0.12345678901234568

Maybe there's something that can be done when precision of a number is greater than that of the default? For comparison, with ipprint,

λ. import Data.Number.BigFloat
λ. let x = 0.123456789012345678901234567890e0
λ. x
    0.12345678901234568
alexeevg commented 11 years ago

Thanks for your report. A little research has shown that parser preserves precision but pretty-printer converts fractional literals to double. I see no easy way to fix it at the moment.