Fix numeric parsing for GHCJS #1681
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The fix from #1647 broke GHCJS support for Dhall. Specifically, any Dhall code containing numeric literals would fail to parse when using GHCJS. The consequence of this is that the final example from the online demo currently does not work because it uses at least one number. The root cause was this issue: ghcjs/ghcjs-base#62 The change to use `Text.Megaparsec.Char.Lexer.float` triggered the above problem, because `float` depended transitively on `Data.Char.toTitle` which was not working for the version of GHCJS that we currently build against. The fix is to reimplement the logic for parsing double literals by following the standard grammar instead of reusing an existing utility. However, I cribbed quite a bit from the existing logic for `Text.Parser.Char.double` along the way.
sjakobi
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Feb 21, 2020
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Nice catch!
Maybe a comment referencing the GHCJS bug might be useful for a future reader who wonders why we don't use a standard float parser?!
Also: Should we try to run the testsuite with GHCJS in CI (and thereby catch such bugs earlier)? Not sure how tricky that would be though…
... as suggested by @sjakobi
For some reason `-- * ${URL}` is not allowed in a comment?
Gabriella439
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Feb 22, 2020
This fixes a GHCJS bug that causes code with numbers to fail to parse See: dhall-lang/dhall-haskell#1681
Gabriella439
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Feb 23, 2020
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The fix from #1647 broke GHCJS support for Dhall. Specifically, any Dhall
code containing numeric literals would fail to parse when using GHCJS.
The consequence of this is that the final example from the online demo
currently does not work because it uses at least one number.
The root cause was this issue:
ghcjs/ghcjs-base#62
The change to use
Text.Megaparsec.Char.Lexer.floattriggered the aboveproblem, because
floatdepended transitively onData.Char.toTitlewhichwas not working for the version of GHCJS that we currently build against.
The fix is to reimplement the logic for parsing double literals by
following the standard grammar instead of reusing an existing utility.
However, I cribbed quite a bit from the existing logic for
Text.Parser.Char.doublealong the way.