72 lines
2.8 KiB
Markdown
72 lines
2.8 KiB
Markdown
# HACKING
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## Design decisions
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### Using [Excepts](https://hackage.haskell.org/package/haskus-utils-variant-3.0/docs/Haskus-Utils-Variant-Excepts.html) as a beefed up ExceptT
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This is an open variant, similar to [plucky](https://hackage.haskell.org/package/plucky) or [oops](https://github.com/i-am-tom/oops) and allows us to combine different error types. Maybe it is too much and it's a little bit [unergonomic](https://github.com/haskus/packages/issues/32) at times. If it really hurts maintenance, it will be removed. It was more of an experiment.
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### No use of haskell-TLS
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I consider haskell-TLS an interesting experiment, but not a battle-tested and peer-reviewed crypto implementation. There is little to no research about what the intricacies of using haskell for low-level crypto are and how vulnerable such binaries are. Instead, we use either curl the binary (for FreeBSD and mac) or http-io-streams, which works with OpenSSL bindings.
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### Optics instead of lens
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They're a little safer (less Monoid weirdness with view) and have better error messages. Consider the following wit lens
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```
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> view (_Just . to (++ "abc")) Nothing
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""
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```
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vs optics
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```
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> view (_Just % to (++ "abc")) Nothing
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<interactive>:2:1: error:
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• An_AffineFold cannot be used as A_Getter
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• In the expression: view (_Just % to (++ "abc")) Nothing
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In an equation for ‘it’: it = view (_Just % to (++ "abc")) Nothing
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```
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### Strict and StrictData on by default
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Kazu Yamamoto [explained it in his PR](https://github.com/yesodweb/wai/pull/752#issuecomment-501531386) very well. I like to agree with him. The instances where we need non-strict behavior, we annotate it.
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## Code style and formatting
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1. Brittany
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2. mtl-style preferred
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3. no overly pointfree style
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## Code structure
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Main functionality is in `GHCup` module. Utility functions are
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organised tree-ish in `GHCup.Utils` and `GHCup.Utils.*`.
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Anything dealing with ghcup specific directories is in
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`GHCup.Utils.Dirs`.
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Download information on where to fetch bindists from is in the appropriate
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yaml files: `ghcup-<yaml-ver>.yaml`.
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## Common Tasks
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### Adding a new GHC version
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1. open the latest `ghcup-<yaml-ver>.yaml`
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2. find the latest ghc version (in yaml tree e.g. `ghcupDownloads -> GHC -> 8.10.3`)
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3. copy-paste it
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4. adjust the version, tags, changelog, source url
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5. adjust the various bindist urls (make sure to also change the yaml anchors)
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6. run `cabal run exe:ghcup-gen -- check-tarballs -f ghcup-<yaml-ver>.yaml -u 'ghc-8\.10\.4'`
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## Major refactors
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1. First major refactor included adding cross support. This added
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`GHCTargetVersion`, which includes the target in addition to the version.
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Most of the `Version` parameters to functions had to be replaced with
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that and ensured the logic is consistent for cross and non-cross
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installs.
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