copilot-prettyprinter: Pretty-print struct update expressions. Refs #526.

[RyanGlScott]

This adds support for pretty-printing expressions that update fields of a struct.

Fixes #526.

[ivanperez-keera]

Change Manager:

• Do we want to use the operators ## and =: instead of printing UpdateField ... at ... to? The answer may be "No", I'm just asking if one is preferable to the other and, if so, why.
• Can you please rebase on top of the current master HEAD?

[RyanGlScott]

• Do we want to use the operators ## and =: instead of printing UpdateField ... at ... to? The answer may be "No", I'm just asking if one is preferable to the other and, if so, why.

Actually, I think I would prefer the use of ## and =: when pretty-printing. The only reason I went with UpdateField was because the in-progress array update patch (see #36) used a similar approach when pretty-printing array updates, and I was just copying prior art.

I'll update the patch to use the infix notation.

Can you please rebase on top of the current master HEAD?

Sure.

[RyanGlScott]

I've pushed a new implementation. Let me know if you'd prefer changing anything about the layout or naming conventions in use.

[ivanperez-keera]

Change Manager: Verified that:

• Solution is implemented:

  • The code proposed compiles and passes all tests. Details:
    Build log: https://app.travis-ci.com/github/Copilot-Language/copilot/builds/272116442

  • The solution proposed produces the expected result. Details:
    The following Dockerfile installs copilot and runs a spec that uses copilot-prettyprinter to pretty print an expression with stream with a struct update in it, followed by "Success":

    --- Dockerfile
    FROM ubuntu:focal
    
    ENV DEBIAN_FRONTEND=noninteractive
    RUN apt-get update
    
    RUN apt-get install --yes libz-dev
    RUN apt-get install --yes git
    
    RUN apt-get install --yes wget
    RUN mkdir -p $HOME/.ghcup/bin
    RUN wget https://downloads.haskell.org/~ghcup/0.1.19.2/x86_64-linux-ghcup-0.1.19.2 -O $HOME/.ghcup/bin/ghcup
    
    RUN chmod a+x $HOME/.ghcup/bin/ghcup
    ENV PATH=$PATH:/root/.ghcup/bin/
    ENV PATH=$PATH:/root/.cabal/bin/
    RUN apt-get install --yes curl
    RUN apt-get install --yes gcc g++ make libgmp3-dev
    RUN apt-get install --yes pkg-config
    
    SHELL ["/bin/bash", "-c"]
    
    RUN ghcup install ghc 9.4
    RUN ghcup install cabal 3.2
    RUN ghcup set ghc 9.4.8
    RUN cabal update
    
    ADD UpdateFieldPP.hs /tmp/UpdateFieldPP.hs
    
    CMD git clone $REPO \
        && cd $NAME \
        && git checkout $COMMIT \
        && cabal v1-sandbox init \
        && cabal v1-install alex happy \
        && cabal v1-install copilot**/ \
        && cabal v1-exec -- runhaskell /tmp/UpdateFieldPP.hs \
        && echo Success
        
    --- UpdateFieldPP.hs
    {-# LANGUAGE DataKinds #-}
    {-# LANGUAGE NoImplicitPrelude #-}
    module Main (main) where
    
    import Data.Foldable (for_)
    import Data.Functor (void)
    import Data.Word (Word32)
    
    import qualified Copilot.PrettyPrint as PP
    import Language.Copilot
    
    data S = S
      { unS :: Field "unS" Word32
      }
    
    instance Struct S where
      typeName _ = "s"
      toValues s = [Value typeOf (unS s)]
    
    instance Typed S where
      typeOf = Struct (S (Field 0))
    
    spec :: Spec
    spec = do
      let externS :: Stream S
          externS = extern "extern_s" Nothing
    
          example :: Stream Word32
          example = (externS ## unS =: 42) # unS
    
      trigger "example" (example == example) [arg externS, arg example]
    
    main :: IO ()
    main = do
      spec' <- reify spec
      putStrLn $ PP.prettyPrint spec'

    Command (substitute variables based on new path after merge):

    $ docker run -e "REPO=https://github.com/GaloisInc/copilot-1" -e "NAME=copilot-1" -e "COMMIT=cc9ca2276e86676ef41393412224cff96c952a61" -it copilot-verify-526
    

• Implementation is documented. Details:
  No new functions are provided; just an update to an existing function.
• Change history is clear.
• Commit messages are clear.
• Changelogs are updated.
• Examples are updated. Details:
  No updates needed.
• Required version bumps are evaluated. Details:
  Bump not needed (bug fix).