I encountered something similar, Apple had been majorly slacking. 

Cabal can't find C++ headers for digest/text on Mac (Sequoia) discourse.haskell.org

On Oct 16, 2024, at 3:53 PM, George Colpitts <george.colpitts@gmail.com> wrote:



It worked for me on my M2 mac but only after uninstalling and reinstalling Command Line Tools. 

Hopefully the problem I had was unique to me. I got an error when I ran  ./configure on my M2 mac:

checking C++ standard library flavour... actest.cpp:1:10: fatal error: 'iostream' file not found
    1 | #include <iostream>
      |          ^~~~~~~~~~
1 error generated.
configure: error: Failed to compile test program

Following is the complete output I got 

checking for opt-17... no
checking for opt-17.0... no
checking for opt17... no
checking for opt-16... no
checking for opt-16.0... no
checking for opt16... no
checking for opt-15... no
checking for opt-15.0... no
checking for opt15... no
checking for opt-14... no
checking for opt-14.0... no
checking for opt14... no
checking for opt-13... no
checking for opt-13.0... no
checking for opt13... no
checking for opt... opt
checking opt version (18.1.8) is between 13 and 20... yes
checking for clang-19... no
checking for clang-19.0... no
checking for clang19... no
checking for clang-18... clang-18
checking clang-18 version (18.1.8) is between 13 and 20... yes
configure: $CC is not gcc; assuming it's a reasonably new C compiler
checking whether CC supports -no-pie... no
checking whether CC supports flags passed by GHC when compiling via C... yes
checking Setting up CFLAGS, LDFLAGS, IGNORE_LINKER_LD_FLAGS and CPPFLAGS... done
checking Setting up CONF_CC_OPTS_STAGE0, CONF_GCC_LINKER_OPTS_STAGE0, CONF_LD_LINKER_OPTS_STAGE0 and CONF_CPP_OPTS_STAGE0... done
checking Setting up CONF_CC_OPTS_STAGE1, CONF_GCC_LINKER_OPTS_STAGE1, CONF_LD_LINKER_OPTS_STAGE1 and CONF_CPP_OPTS_STAGE1... done
checking Setting up CONF_CC_OPTS_STAGE2, CONF_GCC_LINKER_OPTS_STAGE2, CONF_LD_LINKER_OPTS_STAGE2 and CONF_CPP_OPTS_STAGE2... done
checking whether ld64 requires -no_fixup_chains... yes
checking whether ld64 requires -no_fixup_chains... yes
checking whether ld64 requires -no_fixup_chains... yes
checking whether ld64 requires -no_fixup_chains... yes
checking whether the linker requires -no_warn_duplicate_libraries... yes
checking whether the linker requires -no_warn_duplicate_libraries... yes
checking whether the linker requires -no_warn_duplicate_libraries... yes
checking whether ld supports response files... yes
checking C++ standard library flavour... actest.cpp:1:10: fatal error: 'iostream' file not found
    1 | #include <iostream>
      |          ^~~~~~~~~~
1 error generated.
configure: error: Failed to compile test program

On Wed, Oct 16, 2024 at 8:51 AM Zubin Duggal <zubin@well-typed.com> wrote:

The GHC developers are very pleased to announce the availability
of the first alpha release of GHC 9.12.1. Binary distributions, source
distributions, and documentation are available at [downloads.haskell.org][].


We hope to have this release available via ghcup shortly.

GHC 9.12 will bring a number of new features and improvements, including:

  * The new language extension [OrPatterns] allowing you to combine multiple
    pattern clauses into one.

  * The [MultilineStrings] language extension to allow you to more easily write
    strings spanning multiple lines in your source code.

  * Improvements to the OverloadedRecordDot extension, allowing the built-in
    `HasField` class to be used for records with fields of non lifted representations.

  * The [NamedDefaults] language extension has been introduced allowing you to
    define defaults for typeclasses other than `Num`.

  * More deterministic object code output, controlled by the `-fobject-determinism`
    flag, which improves determinism of builds a lot (though does not fully do so)
    at the cost of some compiler performance (1-2%). See #12935 for the details

  * GHC now accepts type syntax in expressions as part of [GHC Proposal #281].

  * ... and many more

A full accounting of changes can be found in the [release notes][].
As always, GHC's release status, including planned future releases, can
be found on the GHC Wiki [status][].

We would like to thank GitHub, IOG, the Zw3rk stake pool,
Well-Typed, Tweag I/O, Serokell, Equinix, SimSpace, the Haskell
Foundation, and other anonymous contributors whose on-going financial
and in-kind support has facilitated GHC maintenance and release
management over the years. Finally, this release would not have been
possible without the hundreds of open-source contributors whose work
comprise this release.

As always, do give this release a try and open a [ticket][] if you see
anything amiss.


[release notes]: https://downloads.haskell.org/ghc/9.12.1-alpha1/docs/users_guide/9.12.1-notes.html
[status]: https://gitlab.haskell.org/ghc/ghc/-/wikis/GHC-status
[downloads.haskell.org]: https://downloads.haskell.org/ghc/9.12.1-alpha1
[ticket]: https://gitlab.haskell.org/ghc/ghc/-/issues/new
[OrPatterns]: https://github.com/ghc-proposals/ghc-proposals/blob/master/proposals/0522-or-patterns.rst
[MultilineStrings]: https://github.com/ghc-proposals/ghc-proposals/blob/master/proposals/0569-multiline-strings.rst
[GHC Proposal #281]: https://github.com/ghc-proposals/ghc-proposals/blob/master/proposals/0281-visible-forall.rst
[NamedDefaults]: https://github.com/ghc-proposals/ghc-proposals/blob/master/proposals/0409-exportable-named-default.rst


Cheers,
Zubin
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