diff --git a/README.md b/README.md index f1ee7fd..85a97cb 100644 --- a/README.md +++ b/README.md @@ -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. -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. @@ -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) * `{ 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. - 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/)! @@ -208,7 +209,7 @@ parser["ROOT"] = [&](const SemanticValues& vs) { auto ret = parser.parse(" item1, item2 "); ``` -The following grammar is same as the above. +The following grammar is the same as the above. ```cpp 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 START <- 'This month is ' MONTH '.' @@ -366,7 +367,7 @@ MONTH <- 'Jan'i | 'January'i | 'Feb'i | 'February'i | '...'i 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 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. @@ -508,20 +509,20 @@ auto ret = ROOT.parse(" [tag1] [tag:2] [tag-3] "); The following are available operators: -| Operator | Description | Operator | Description | -| :------- | :------------------------------ | :------- | :------------------- | -| seq | Sequence | cho | Prioritized Choice | -| zom | Zero or More | oom | One or More | -| opt | Optional | apd | And predicate | -| npd | Not predicate | lit | Literal string | -| liti | Case-insensitive Literal string | cls | Character class | -| ncls | Negated Character class | chr | Character | -| dot | Any character | tok | Token boundary | -| ign | Ignore semantic value | csc | Capture scope | -| cap | Capture | bkr | Back reference | -| dic | Dictionary | pre | Infix expression | -| rec | Infix expression | usr | User defined parser | -| rep | Repetition | | | +| Operator | Description | Operator | Description | +|:---------|:--------------------------------|:---------|:--------------------| +| seq | Sequence | cho | Prioritized Choice | +| zom | Zero or More | oom | One or More | +| opt | Optional | apd | And predicate | +| npd | Not predicate | lit | Literal string | +| liti | Case-insensitive Literal string | cls | Character class | +| ncls | Negated Character class | chr | Character | +| dot | Any character | tok | Token boundary | +| ign | Ignore semantic value | csc | Capture scope | +| cap | Capture | bkr | Back reference | +| dic | Dictionary | pre | Infix expression | +| rec | Infix expression | usr | User defined parser | +| rep | Repetition | | | 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. -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: @@ -599,7 +600,7 @@ stmtb ← (!(Stmt / 'else' / '}') .)* { error_message "invalid statement" 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: @@ -644,7 +645,7 @@ CODE <- < '0x' [a-fA-F0-9]+ > { error_message '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 --------------------------------