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79 lines
3.1 KiB
Plaintext
79 lines
3.1 KiB
Plaintext
{0 Catala surface representation }
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This representation is the first in the compilation chain
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(see {{: index.html#architecture} Architecture}). Its purpose is to
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host the output of the Catala parser, before any transformations have been made.
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The module describing the abstract syntax tree is:
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{!modules: Surface.Ast}
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This representation can also be weaved into literate programming outputs
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using the {{:literate.html} literate programming modules}.
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{1 Lexing }
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The lexing in the Catala compiler is done using
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{{: https://github.com/ocaml-community/sedlex} sedlex}, the modern OCaml lexer
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that offers full support for UTF-8. This support enables users of non-English
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languages to use their favorite diacritics and symbols in their code.
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While the parser of Catala is unique, three different lexers can be used to
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produce the parser tokens.
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{ul
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{li {!module: Surface.Lexer_common} corresponds to a concise and programming-language-like
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syntax for Catala. Examples of this syntax can be found in the test suite
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of the compiler.}
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{li {!module: Surface.Lexer_en} is the adaptation of {!module: Surface.Lexer_common}
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with verbose English keywords matching legal concepts.}
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{li {!module: Surface.Lexer_fr} is the adaptation of {!module: Surface.Lexer_common}
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with verbose French keywords matching legal concepts.}
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}
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Relevant modules:
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{!modules: Surface.Lexer_common Surface.Lexer_fr Surface.Lexer_en}
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{1 Parsing }
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The Catala compiler uses {{: http://cambium.inria.fr/~fpottier/menhir/} Menhir}
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to perform its parsing.
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{!module: Surface.Parser} is the main file where the parser tokens and the
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grammar is declared. It is automatically translated into its parsing automata
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equivalent by Menhir.
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In order to provide decent syntax error messages, the Catala compiler uses the
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novel error handling provided by Menhir and detailed in Section 11 of the
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{{: http://cambium.inria.fr/~fpottier/menhir/manual.pdf} Menhir manual}.
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A [parser.messages] source file has been manually annotated with custom
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error message for every potential erroneous state of the parser, and Menhir
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automatically generated the {!module: Surface.Parser_errors} module containing
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the function linking the erroneous parser states to the custom error message.
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To wrap it up, {!module: Surface.Parser_driver} glues all the parsing and
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lexing together to perform the translation from source code to abstract syntax
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tree, with meaningful error messages.
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Relevant modules:
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{!modules: Surface.Parser Surface.Parser_driver Surface.Parser_errors}
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{1 Name resolution and translation }
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The desugaring consists of translating {!module: Surface.Ast} to
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{!module: Desugared.Ast} of the {{: desugared.html} desugared representation}.
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The translation is implemented in
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{!module:Desugared.From_surface}, but it relies on a helper module to perform the
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name resolution: {!module:Desugared.Name_resolution}. Indeed, in
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{!module: Surface.Ast}, the variables identifiers are just [string], whereas in
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{!module: Desugared.Ast} they have been turned into well-categorized types
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with an unique identifier like {!type:Shared_ast.ScopeName.t}.
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Relevant modules:
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{!modules: Desugared.Name_resolution Desugared.From_surface}
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