david-christiansen / final-pretty-printer Goto Github PK
View Code? Open in Web Editor NEWA monadic (and pretty) pretty printer for Haskell
License: MIT License
A monadic (and pretty) pretty printer for Haskell
License: MIT License
We were debugging an issue with the SML version of final-pretty-printer
and came across what may be a logic error in the chunk
algorithm.
In short, there is the following code which determines whether to raise a fault:
w <- measureCurLine
n <- askNesting
when (n + w > wmax) empty
when (w > rmax) empty
Observe that when nesting is enacted (through newline
), spaces of the appropriate width are added to the current line (using chunk
). So, in this part of chunk
, it looks like this whitespace is counted twice: first in the size of the current line w
, and second in the nesting n
. Concretely, this results in code being too aggressively broken, when there is sufficient width for it to remain flat.
We believe that this code can be changed to the following:
w <- measureCurLine
n <- askNesting
when (w > wmax) empty
when (w - n > rmax) empty
We have tried this change out in our SML port, and it appears to give the correct result. What do you think?
--- @jonsterling and @cangiuli
Using Stack with LTS-15.15 and GHC 8.8.3, I had to use allow-newer
to build final-pretty-printer
. Perhaps relax the upper bounds?
WARNING: Ignoring final-pretty-printer's bounds on ansi-terminal (==0.6.*); using ansi-terminal-0.10.3.
Reason: allow-newer enabled.
WARNING: Ignoring final-pretty-printer's bounds on base (>=4.3 && <4.10); using base-4.13.0.0.
Reason: allow-newer enabled.
WARNING: Ignoring final-pretty-printer's bounds on containers (==0.5.*); using containers-0.6.2.1.
Reason: allow-newer enabled.
WARNING: Ignoring final-pretty-printer's bounds on exceptions (==0.8.*); using exceptions-0.10.4.
Reason: allow-newer enabled.
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