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Fix grammar, punctuation, and formatting in README.md (#313)

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@ -5,7 +5,8 @@ cpp-peglib
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. 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.
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) Since this library only supports C++17 compilers, please make sure that the compiler option `-std=c++17` is enabled.
(`/std:c++17 /Zc:__cplusplus` for MSVC)
You can also try the online version, PEG Playground at https://yhirose.github.io/cpp-peglib. You can also try the online version, PEG Playground at https://yhirose.github.io/cpp-peglib.
@ -34,11 +35,11 @@ The PEG syntax is well described on page 2 in the [document](http://www.brynosau
* `label { error_message "..." }` (Error message instruction) * `label { error_message "..." }` (Error message instruction)
* `{ no_ast_opt }` (No AST node optimization instruction) * `{ no_ast_opt }` (No AST node optimization instruction)
'End of Input' check will be done as default. In order to disable the check, please call `disable_eoi_check`. 'End of Input' check will be done as default. To disable the check, please call `disable_eoi_check`.
This library supports the linear-time parsing known as the [*Packrat*](http://pdos.csail.mit.edu/~baford/packrat/thesis/thesis.pdf) parsing. This library supports the linear-time parsing known as the [*Packrat*](http://pdos.csail.mit.edu/~baford/packrat/thesis/thesis.pdf) parsing.
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). 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).
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/)! 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/)!
@ -208,7 +209,7 @@ parser["ROOT"] = [&](const SemanticValues& vs) {
auto ret = parser.parse(" item1, item2 "); auto ret = parser.parse(" item1, item2 ");
``` ```
The following grammar is same as the above. The following grammar is the same as the above.
```cpp ```cpp
peg::parser parser(R"( peg::parser parser(R"(
@ -356,7 +357,7 @@ parser["MONTH"] = [](const SemanticValues &vs) {
}; };
``` ```
It supports the case insensitive mode. It supports the case-insensitive mode.
```peg ```peg
START <- 'This month is ' MONTH '.' START <- 'This month is ' MONTH '.'
@ -366,7 +367,7 @@ MONTH <- 'Jan'i | 'January'i | 'Feb'i | 'February'i | '...'i
Cut operator Cut operator
------------ ------------
`↑` operator could mitigate backtrack performance problem, but has a risk to change the meaning of grammar. `↑` operator could mitigate the backtrack performance problem, but has a risk to change the meaning of grammar.
```peg ```peg
S <- '(' ↑ P ')' / '"' ↑ P '"' / P S <- '(' ↑ P ')' / '"' ↑ P '"' / P
@ -479,7 +480,7 @@ if (parser.parse("...", ast)) {
} }
``` ```
`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. `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.
It internally calls `peg::AstOptimizer` to do the job. You can make your own AST optimizers to fit your needs. It internally calls `peg::AstOptimizer` to do the job. You can make your own AST optimizers to fit your needs.
@ -508,20 +509,20 @@ auto ret = ROOT.parse(" [tag1] [tag:2] [tag-3] ");
The following are available operators: The following are available operators:
| Operator | Description | Operator | Description | | Operator | Description | Operator | Description |
| :------- | :------------------------------ | :------- | :------------------- | |:---------|:--------------------------------|:---------|:--------------------|
| seq | Sequence | cho | Prioritized Choice | | seq | Sequence | cho | Prioritized Choice |
| zom | Zero or More | oom | One or More | | zom | Zero or More | oom | One or More |
| opt | Optional | apd | And predicate | | opt | Optional | apd | And predicate |
| npd | Not predicate | lit | Literal string | | npd | Not predicate | lit | Literal string |
| liti | Case-insensitive Literal string | cls | Character class | | liti | Case-insensitive Literal string | cls | Character class |
| ncls | Negated Character class | chr | Character | | ncls | Negated Character class | chr | Character |
| dot | Any character | tok | Token boundary | | dot | Any character | tok | Token boundary |
| ign | Ignore semantic value | csc | Capture scope | | ign | Ignore semantic value | csc | Capture scope |
| cap | Capture | bkr | Back reference | | cap | Capture | bkr | Back reference |
| dic | Dictionary | pre | Infix expression | | dic | Dictionary | pre | Infix expression |
| rec | Infix expression | usr | User defined parser | | rec | Infix expression | usr | User defined parser |
| rep | Repetition | | | | rep | Repetition | | |
Adjust definitions Adjust definitions
------------------ ------------------
@ -567,7 +568,7 @@ cpp-peglib supports the furthest failure error position report as described in t
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. 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.
The custom message supports `%t` which is a place holder for the unexpected token, and `%c` for the unexpected Unicode char. The custom message supports `%t` which is a placeholder for the unexpected token, and `%c` for the unexpected Unicode char.
Here is an example of Java-like grammar: Here is an example of Java-like grammar:
@ -599,7 +600,7 @@ stmtb ← (!(Stmt / 'else' / '}') .)* { error_message "invalid statement"
condw ← &'==' ('==' RelExp)* / &'<' ('<' AddExp)* / (!')' .)* condw ← &'==' ('==' RelExp)* / &'<' ('<' AddExp)* / (!')' .)*
``` ```
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.". 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."
Here is the result: Here is the result:
@ -644,7 +645,7 @@ CODE <- < '0x' [a-fA-F0-9]+ > { error_message 'code format error...' }
custom_message.txt:1:8: code format error... custom_message.txt:1:8: code format error...
``` ```
NOTE: If there are more than one elements with error message instruction in a prioritized choice, this feature may not work as you expect. 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.
Change the Start Definition Rule Change the Start Definition Rule
-------------------------------- --------------------------------