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62 lines
2.7 KiB
ReStructuredText
62 lines
2.7 KiB
ReStructuredText
**************************
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Frequently Asked Questions
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**************************
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Can Idris 2 compile itself?
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===========================
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Yes, Idris 2 is implemented in Idris 2. By default, it targets
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`Chez Scheme <https://cisco.github.io/ChezScheme/>`_, so you can bootstrap
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from the generated Scheme code, as described in Section :ref:`sect-starting`.
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Why does Idris 2 target Scheme? Surely a dynamically typed target language is going to be slow?
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===============================================================================================
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You may be surprised at how fast Chez Scheme is :). `Racket <https://download.racket-lang.org/>`_,
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as an alternative target, also performs well. Both perform better than the
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Idris 1 back end, which is written in C but has not had the decades of
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engineering effort by run time system specialists that Chez and Racket have.
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Chez Scheme also allows us to turn off run time checks, which we do.
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As anecdotal evidence of the performance improvement, as of 23rd May 2020, on a
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Dell XPS 13 running Ubuntu, the performance is:
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* Idris 2 (with the Chez Scheme runtime) checks its own source in 93 seconds.
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* The bootstrapping Idris 2 (compiled with Idris 1) checks the same source in 125s.
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* Idris 1 checks the bootstrapping Idris 2's source (the same as the above,
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but with minor variations due to the syntax changes) in 768 seconds.
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This is, nevertheless, not intended to be a long term solution, even if it
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is a very convenient way to bootstrap.
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Can Idris 2 generate Javascript? What about plug-in code generators?
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====================================================================
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Not yet, but there is a Javascript code generator in development.
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Like Idris 1, Idris 2 will support plug-in code generation to allow you to
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write a back end for the platform of your choice, but this is not yet
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implemented.
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What are the main differences between Idris 1 and Idris 2?
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==========================================================
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The most important difference is that Idris 2 explicitly represents *erasure*
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in types, so that you can see at compile time which function and data type
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arguments are erased, and which will be present at run time. You can see more
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details in :ref:`sect-multiplicities`.
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Idris 2 has significantly better type checking performance (perhaps even an
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order of magnitude!) and generates significantly better code.
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Also, being implemented in Idris, we've been able to take advantage of the
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type system to remove some significant sources of bugs!
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You can find more details in Section :ref:`updates-index`.
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Where can I find more answers?
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==============================
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The `Idris 1 FAQ <https://docs.idris-lang.org/en/latest/faq/faq.html>`_ is
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mostly still relevant.
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