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proxy.golang.org : modernc.org/yy

Command yy processes yacc source code and produces three output files: - A Go file containing definitions of AST nodes. - A Go file containing documentation examples[0] of productions defined by the yacc grammar. - A new yacc file with automatic actions instantiating the AST nodes. To install yy http://godoc.org/modernc.org/yy Invocation: Flags handled by the yy command: 2019-02-27: Added -position flag. 2017-10-23: Added the case directive. A partial example: see the testdata directory and files The three output files were generated by A more complete, working project using yy can be found at http://godoc.org/modernc.org/pl0 Every rule is turned into a definition of a struct type in ast.go (adjust using the -ast flag). The fields of the type are a sum of all productions (cases) of the rule. The generated type will be something like In the above, Foo and Bar fields will be non nill when Case is 0 and Foo and Baz fields will be non nil when Case is 1. The above holds when both Foo and Bar are non terminal symbols. If the production(s) contain also terminal symbols, all those symbols are turned into fields named Token with an optional numeric suffix when more than one non terminal appears in any of the production(s). The generated type will be like In the above, Token will capture '+' when Case is 0. For Case 1, Token will capture '[', Token2 NUMBER and Token3 ']'. MyTokenType is the type defined in the yacc %union as in It is assumed that the lexer passed as an argument to yyParse instantiantes the lval.Token field with additional token information, like the lexeme value, starting position in the file etc. There's a direct mapping, though not in the same order, of yacc pseudo variables $1, $2, ... and fields of the generated node types. For every production not disabled by the yy:ignore direction, yy injects code for instantiating the AST node when the production is reduced. For example, this rule from input.y having no semantic action is turned into in output.y. The default yacc type of AST nodes is 'node' and can be changed using the -node flag. Option-like rules, for example as in in output.y, ie. the empty case does not produce a &RuleOpt{}, but nil instead to conserve space. Generated examples depend on an user supplied function, by default named exampleAST, with a signature This function is called with the production number, as assigned by goyacc and an example string generated by yy. exampleAST should parse the example string and return the AST created when production rule is reduced. When the project's parser is not yet working, a dummy exampleAST function returnin always nil is a workaround. yy inspects rule actions found in the input file. If the action code mentions identifier lx, yy asumes it refers to the yyLexer passed to yyParse. In that case code like is injected near the beginning of the semantic action. The specific type into which the yylex parameter is type asserted is adjustable using the -yylex flag. Similarly, when identifier lhs is mentioned, a short variable definiton of variable lhs, like is injected into the output.y action, replacing the default generated action (see "Concepts") For example, an action in input.y Produces in output.y. The AST examples generator depends on presence of the yy:token directive for all non constant terminal symbols or the presence of the constant token value as in this example The AST examples yy generates must be post processed by using the fe command (http://godoc.org/modernc.org/fe), for example One of the reasons why this is not done automatically by yy is that the above command will succeed only after your project has a _working_ scanner/parser combination. That's not the case in the early stages. yy recognizes specially formatted comments within the input as directives. All directive have the format Note that the directive must follow immediately the comment opening. There must be no empty line(s) between the directive and the production it aplies to. For example The argument of the example directive is a doubly quoted Go string. The string is used instead of an automatically generated example. For example The argument of the field directive is the text up to the end of the comment. The argument is added to the automatically generated fields of the node type of Rule. For example The ignore directive has no arguments. The directive disables generating of the node type of Rule as well as generating code instantiating such node. For example The list directive has no arguments. yy by default detects all left recursive rules. When such rule has name having suffix 'List', yy automatically generates proper reversing of the rule items. Using the list directive enables the same when such a left recursive rule does not have suffix 'List' in its name. For example The argument of the token directive is a doubly quoted Go string. The string is passed to a fmt.Sprinf call with an numeric argument chosen by yy that falls small ASCII letters. The resulting string is used to generate textual token values in examples. For example The argument of the case directive is an identifier, which is appended to the rule name to produce a symbolic and typed case number value. The type name is <RuleName>Case.

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purl: pkg:golang/modernc.org/yy
License: BSD-3-Clause
Latest release: about 1 year ago
First release: over 5 years ago
Namespace: modernc.org
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