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Fix grammar, punctuation, and formatting in README.md (#313)
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Patrick Scheibe
GitHub
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README.md
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README.md
@ -5,7 +5,8 @@ cpp-peglib
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C++17 header-only [PEG](http://en.wikipedia.org/wiki/Parsing_expression_grammar) (Parsing Expression Grammars) library. You can start using it right away just by including `peglib.h` in your project.
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Since this library only supports C++17 compilers, please make sure that compiler the option `-std=c++17` is enabled. (`/std:c++17 /Zc:__cplusplus` for MSVC)
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Since this library only supports C++17 compilers, please make sure that the compiler option `-std=c++17` is enabled.
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(`/std:c++17 /Zc:__cplusplus` for MSVC)
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You can also try the online version, PEG Playground at https://yhirose.github.io/cpp-peglib.
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@ -34,11 +35,11 @@ The PEG syntax is well described on page 2 in the [document](http://www.brynosau
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* `label { error_message "..." }` (Error message instruction)
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* `{ no_ast_opt }` (No AST node optimization instruction)
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'End of Input' check will be done as default. In order to disable the check, please call `disable_eoi_check`.
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'End of Input' check will be done as default. To disable the check, please call `disable_eoi_check`.
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This library supports the linear-time parsing known as the [*Packrat*](http://pdos.csail.mit.edu/~baford/packrat/thesis/thesis.pdf) parsing.
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IMPORTANT NOTE for some Linux distributions such as Ubuntu and CentOS: Need `-pthread` option when linking. See [#23](https://github.com/yhirose/cpp-peglib/issues/23#issuecomment-261126127), [#46](https://github.com/yhirose/cpp-peglib/issues/46#issuecomment-417870473) and [#62](https://github.com/yhirose/cpp-peglib/issues/62#issuecomment-492032680).
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IMPORTANT NOTE for some Linux distributions such as Ubuntu and CentOS: Need `-pthread` option when linking. See [#23](https://github.com/yhirose/cpp-peglib/issues/23#issuecomment-261126127), [#46](https://github.com/yhirose/cpp-peglib/issues/46#issuecomment-417870473) and [#62](https://github.com/yhirose/cpp-peglib/issues/62#issuecomment-492032680).
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I am sure that you will enjoy this excellent ["Practical parsing with PEG and cpp-peglib"](https://berthub.eu/articles/posts/practical-peg-parsing/) article by [bert hubert](https://berthub.eu/)!
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@ -208,7 +209,7 @@ parser["ROOT"] = [&](const SemanticValues& vs) {
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auto ret = parser.parse(" item1, item2 ");
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```
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The following grammar is same as the above.
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The following grammar is the same as the above.
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```cpp
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peg::parser parser(R"(
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@ -356,7 +357,7 @@ parser["MONTH"] = [](const SemanticValues &vs) {
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};
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```
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It supports the case insensitive mode.
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It supports the case-insensitive mode.
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```peg
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START <- 'This month is ' MONTH '.'
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@ -366,7 +367,7 @@ MONTH <- 'Jan'i | 'January'i | 'Feb'i | 'February'i | '...'i
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Cut operator
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------------
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`↑` operator could mitigate backtrack performance problem, but has a risk to change the meaning of grammar.
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`↑` operator could mitigate the backtrack performance problem, but has a risk to change the meaning of grammar.
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```peg
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S <- '(' ↑ P ')' / '"' ↑ P '"' / P
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@ -479,7 +480,7 @@ if (parser.parse("...", ast)) {
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}
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```
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`optimize_ast` removes redundant nodes to make a AST simpler. If you want to disable this behavior from particular rules, `no_ast_opt` instruction can be used.
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`optimize_ast` removes redundant nodes to make an AST simpler. If you want to disable this behavior from particular rules, `no_ast_opt` instruction can be used.
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It internally calls `peg::AstOptimizer` to do the job. You can make your own AST optimizers to fit your needs.
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@ -508,20 +509,20 @@ auto ret = ROOT.parse(" [tag1] [tag:2] [tag-3] ");
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The following are available operators:
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| Operator | Description | Operator | Description |
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| :------- | :------------------------------ | :------- | :------------------- |
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| seq | Sequence | cho | Prioritized Choice |
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| zom | Zero or More | oom | One or More |
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| opt | Optional | apd | And predicate |
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| npd | Not predicate | lit | Literal string |
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| liti | Case-insensitive Literal string | cls | Character class |
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| ncls | Negated Character class | chr | Character |
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| dot | Any character | tok | Token boundary |
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| ign | Ignore semantic value | csc | Capture scope |
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| cap | Capture | bkr | Back reference |
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| dic | Dictionary | pre | Infix expression |
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| rec | Infix expression | usr | User defined parser |
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| rep | Repetition | | |
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| Operator | Description | Operator | Description |
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|:---------|:--------------------------------|:---------|:--------------------|
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| seq | Sequence | cho | Prioritized Choice |
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| zom | Zero or More | oom | One or More |
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| opt | Optional | apd | And predicate |
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| npd | Not predicate | lit | Literal string |
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| liti | Case-insensitive Literal string | cls | Character class |
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| ncls | Negated Character class | chr | Character |
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| dot | Any character | tok | Token boundary |
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| ign | Ignore semantic value | csc | Capture scope |
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| cap | Capture | bkr | Back reference |
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| dic | Dictionary | pre | Infix expression |
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| rec | Infix expression | usr | User defined parser |
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| rep | Repetition | | |
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Adjust definitions
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------------------
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@ -567,7 +568,7 @@ cpp-peglib supports the furthest failure error position report as described in t
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For better error report and recovery, cpp-peglib supports 'recovery' operator with label which can be associated with a recovery expression and a custom error message. This idea comes from the fantastic ["Syntax Error Recovery in Parsing Expression Grammars"](https://arxiv.org/pdf/1806.11150.pdf) paper by Sergio Medeiros and Fabio Mascarenhas.
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The custom message supports `%t` which is a place holder for the unexpected token, and `%c` for the unexpected Unicode char.
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The custom message supports `%t` which is a placeholder for the unexpected token, and `%c` for the unexpected Unicode char.
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Here is an example of Java-like grammar:
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@ -599,7 +600,7 @@ stmtb ← (!(Stmt / 'else' / '}') .)* { error_message "invalid statement"
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condw ← &'==' ('==' RelExp)* / &'<' ('<' AddExp)* / (!')' .)*
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```
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For instance, `';'^semi` is a syntactic sugar for `(';' / %recovery(semi))`. `%recover` operator tries to recover the error at ';' by skipping input text with the recovery expression `semi`. Also `semi` is associated with a custom message "missing semicolon in assignment.".
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For instance, `';'^semi` is a syntactic sugar for `(';' / %recovery(semi))`. `%recover` operator tries to recover the error at ';' by skipping input text with the recovery expression `semi`. Also `semi` is associated with a custom message "missing semicolon in assignment."
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Here is the result:
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@ -644,7 +645,7 @@ CODE <- < '0x' [a-fA-F0-9]+ > { error_message 'code format error...' }
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custom_message.txt:1:8: code format error...
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```
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NOTE: If there are more than one elements with error message instruction in a prioritized choice, this feature may not work as you expect.
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NOTE: If there is more than one element with an error message instruction in a prioritized choice, this feature may not work as you expect.
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Change the Start Definition Rule
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--------------------------------
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