100 lines
4.0 KiB
Markdown
100 lines
4.0 KiB
Markdown
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# Examples in C
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This directory contains simple examples of Bison grammar files in C.
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Some of them come from the documentation, which should be installed together
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with Bison. The URLs are provided for convenience.
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## rpcalc - Reverse Polish Notation Calculator
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The first example is that of a simple double-precision Reverse Polish
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Notation calculator (a calculator using postfix operators). This example
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provides a good starting point, since operator precedence is not an issue.
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Extracted from the documentation: [Reverse Polish Notation
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Calculator](https://www.gnu.org/software/bison/manual/html_node/RPN-Calc.html).
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## calc - Simple Calculator
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This example is slightly more complex than rpcalc: it features infix
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operators (`1 + 2`, instead of `1 2 +` in rpcalc), but it does so using a
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unambiguous grammar of the arithmetic instead of using precedence
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directives (%left, etc.).
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## mfcalc - Multi-Function Calculator
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A more complete C example: a multi-function calculator. More complex than
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the previous example. Using precedence directives to support infix
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operators.
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Extracted from the documentation: [Multi-Function Calculator:
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mfcalc](https://www.gnu.org/software/bison/manual/html_node/Multi_002dfunction-Calc.html).
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## lexcalc - calculator with Flex and Bison
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The calculator with precedence directives and location tracking. It uses
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Flex to generate the scanner.
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## reccalc - recursive calculator with Flex and Bison
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This example builds on top of the previous one to provide a reentrant
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parser. Such parsers can be called concurrently in different threads, or
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even recursively. To demonstrate this feature, expressions in parentheses
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are tokenized as strings, and then recursively parsed from the parser. So
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`(((1)+(2))*((3)+(4)))` uses eight parsers, with a depth of four.
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## pushcalc - calculator implemented with a push parser
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All the previous examples are so called "pull parsers": the user invokes the
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parser once, which repeatedly calls the scanner until the input is drained.
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This example demonstrates the "push parsers": the user calls the scanner to
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fetch the next token, passes it to the parser, and repeats the operation
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until the input is drained.
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This example is a straightforward conversion of the 'calc' example to the
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push-parser model.
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## bistromathic - all the bells and whistles
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This example demonstrates best practices when using Bison.
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- Its hand-written scanner tracks locations.
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- Its interface is pure.
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- It uses %params to pass user information to the parser and scanner.
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- Its scanner uses the `error` token to signal lexical errors and enter
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error recovery.
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- Its interface is "incremental", well suited for interaction: it uses the
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push-parser API to feed the parser with the incoming tokens.
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- It features an interactive command line with completion based on the
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parser state, based on `yyexpected_tokens`.
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- It uses Bison's standard catalog for internationalization of generated
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messages.
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- It uses a custom syntax error with location, lookahead correction and
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token internationalization.
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- Error messages quote the source with squiggles that underline the error:
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```
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> 123 456
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1.5-7: syntax error: expected end of file or + or - or * or / or ^ before number
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1 | 123 456
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| ^~~
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```
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- It supports debug traces with semantic values.
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- It uses named references instead of the traditional $1, $2, etc.
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<!---
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Local Variables:
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fill-column: 76
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ispell-dictionary: "american"
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End:
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Copyright (C) 2018-2021 Free Software Foundation, Inc.
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This file is part of GNU bison, the GNU Compiler Compiler.
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Permission is granted to copy, distribute and/or modify this document
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under the terms of the GNU Free Documentation License, Version 1.3 or
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any later version published by the Free Software Foundation; with no
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Invariant Sections, with no Front-Cover Texts, and with no Back-Cover
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Texts. A copy of the license is included in the "GNU Free
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Documentation License" file as part of this distribution.
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LocalWords: mfcalc calc parsers yy rpcalc lexcalc redux reccalc ispell
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LocalWords: reentrant tokenized american postfix pushcalc bistromathic
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LocalWords: lookahead
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-->
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