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@ -10,7 +10,7 @@ Since this library only supports C++17 compilers, please make sure that compiler
You can also try the online version, PEG Playground at https://yhirose.github.io/cpp-peglib.
The PEG syntax is well described on page 2 in the [document](http://www.brynosaurus.com/pub/lang/peg.pdf). *cpp-peglib* also supports the following additional syntax for now:
The PEG syntax is well described on page 2 in the [document](http://www.brynosaurus.com/pub/lang/peg.pdf) by Bran Ford. *cpp-peglib* also supports the following additional syntax for now:
* `'...'i` (Case-insensitive literal operator)
* `[^...]` (Negated character class operator)
@ -49,13 +49,13 @@ using namespace std;
int main(void) {
// (2) Make a parser
parser parser(R"(
# Grammar for Calculator...
Additive <- Multitive '+' Additive / Multitive
Multitive <- Primary '*' Multitive / Primary
Primary <- '(' Additive ')' / Number
Number <- < [0-9]+ >
%whitespace <- [ \t]*
)");
# Grammar for Calculator...
Additive <- Multitive '+' Additive / Multitive
Multitive <- Primary '*' Multitive / Primary
Primary <- '(' Additive ')' / Number
Number <- < [0-9]+ >
%whitespace <- [ \t]*
)");
assert(static_cast<bool>(parser) == true);
@ -96,12 +96,12 @@ To show syntax errors in grammar text:
```cpp
auto grammar = R"(
# Grammar for Calculator...
Additive <- Multitive '+' Additive / Multitive
Multitive <- Primary '*' Multitive / Primary
Primary <- '(' Additive ')' / Number
Number <- < [0-9]+ >
%whitespace <- [ \t]*
# Grammar for Calculator...
Additive <- Multitive '+' Additive / Multitive
Multitive <- Primary '*' Multitive / Primary
Primary <- '(' Additive ')' / Number
Number <- < [0-9]+ >
%whitespace <- [ \t]*
)";
parser parser;
@ -508,6 +508,73 @@ Unicode support
cpp-peglib accepts UTF8 text. `.` matches a Unicode codepoint. Also, it supports `\u????`.
Error report and recovery
-------------------------
cpp-peglib supports the furthest failure error posision report as descrived in the Bryan Ford original document.
For better error report and recovery, cpp-peglib supports 'recovery' operator with label which can be assosiated 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.
Here is an example of Java-like grammar:
```peg
Prog ← 'public' 'class' NAME '{' 'public' 'static' 'void' 'main' '(' 'String' '[' ']' NAME ')' BlockStmt '}'
BlockStmt ← '{' (!'}' Stmt^stmtb)* '}'^rcblk # Annotated with `stmtb` and `rcblk`
Stmt ← IfStmt / WhileStmt / PrintStmt / DecStmt / AssignStmt / BlockStmt
IfStmt ← 'if' '(' Exp ')' Stmt ('else' Stmt)?
WhileStmt ← 'while' '(' Exp^condw ')' Stmt # Annotated with `condw`
DecStmt ← 'int' NAME ('=' Exp)? ';'
AssignStmt ← NAME '=' Exp ';'^semia # Annotated with `semi`
PrintStmt ← 'System.out.println' '(' Exp ')' ';'
Exp ← RelExp ('==' RelExp)*
RelExp ← AddExp ('<' AddExp)*
AddExp ← MulExp (('+' / '-') MulExp)*
MulExp ← AtomExp (('*' / '/') AtomExp)*
AtomExp ← '(' Exp ')' / NUMBER / NAME
NUMBER ← < [0-9]+ >
NAME ← < [a-zA-Z_][a-zA-Z_0-9]* >
%whitespace ← [ \t\n]*
%word ← NAME
# Recovery operator labels
rcblk ← SkipToRCUR { message "missing end of block." }
semia ← '' { message "missing simicolon in assignment." }
stmtb ← (!(Stmt / 'else' / '}') .)* { message "invalid statement" }
condw ← &'==' ('==' RelExp)* / &'<' ('<' AddExp)* / (!')' .)*
# Recovery expressions
SkipToRCUR ← (!'}' ('{' SkipToRCUR / .))* '}'
```
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 assosiated with a custom message "missing simicolon in assignment.".
Here is the result:
```java
public class Example {
public static void main(String[] args) {
int n = 5;
int f = 1;
while( < n) {
f = f * n;
n = n - 1
};
System.out.println(f);
}
}
```
```
> peglint sample_java.peg sample.java
sample.java:5:12: syntax error, unexpected '<', expecting <NAME>, <NUMBER>, <WhileStmt>.
sample.java:8:5: missing simicolon in assignment.
sample.java:8:6: invalid statement
```
As you can see, it can now show more than one error, and provide more meaningfull error messages than the default messages.
peglint - PEG syntax lint utility
---------------------------------
@ -523,44 +590,28 @@ peglint - PEG syntax lint utility
usage: grammar_file_path [source_file_path]
options:
--source: source text
--ast: show AST tree
--opt, --opt-all: optimaze all AST nodes except nodes selected with --opt-rules
--opt-only: optimaze only AST nodes selected with --opt-rules
--opt-rules rules: comma delimitted definition rules for optimazation
--source: source text
--opt-rules rules: CSV definition rules to adjust AST optimazation
--trace: show trace messages
```
### Lint grammar
### Grammar check
```
> cat a.peg
A <- 'hello' ^ 'world'
Additive <- Multitive '+' Additive / Multitive
Multitive <- Primary '*' Multitive / Primary
Primary <- '(' Additive ')' / Number
%whitespace <- [ \t\r\n]*
> peglint a.peg
a.peg:1:14: syntax error
[commendline]:3:35: 'Number' is not defined.
```
```
> cat a.peg
A <- B
> peglint a.peg
a.peg:1:6: 'B' is not defined.
```
```
> cat a.peg
A <- B / C
B <- 'b'
C <- A
> peglint a.peg
a.peg:1:10: 'C' is left recursive.
a.peg:3:6: 'A' is left recursive.
```
### Lint source text
### Source check
```
> cat a.peg
@ -574,6 +625,8 @@ Number <- < [0-9]+ >
[commendline]:1:3: syntax error
```
### AST
```
> cat a.txt
1 + 2 * 3
@ -592,6 +645,8 @@ Number <- < [0-9]+ >
- Number (3)
```
### AST optimazation
```
> peglint --ast --opt --source "1 + 2 * 3" a.peg
+ Additive
@ -633,16 +688,10 @@ Sample codes
* [Calculator (AST version)](https://github.com/yhirose/cpp-peglib/blob/master/example/calc3.cc)
* [Calculator (parsing expressions by precedence climbing)](https://github.com/yhirose/cpp-peglib/blob/master/example/calc4.cc)
* [Calculator (AST version and parsing expressions by precedence climbing)](https://github.com/yhirose/cpp-peglib/blob/master/example/calc5.cc)
* [Monkey language](https://github.com/yhirose/monkey-cpp) described in [Writing An Interpreter In Go](https://interpreterbook.com/).
* [PL/0 language example](https://github.com/yhirose/cpp-peglib/blob/master/pl0/pl0.cc)
* [A tiny PL/0 JIT compiler in less than 700 LOC with LLVM and PEG parser](https://github.com/yhirose/pl0-jit-compiler)
* [A Programming Language just for writing Fizz Buzz program. :)](https://github.com/yhirose/fizzbuzzlang)
PEG debug
---------
A debug viewer for Parsing Expression Grammars using cpp-peglib by [mqnc](https://github.com/mqnc). Please see [his gihub project page](https://github.com/mqnc/pegdebug) for the detail. You can see a parse result of PL/0 code [here](https://mqnc.github.io/pegdebug/example/output.html).
License
-------

2
lint/README.md
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@ -32,7 +32,7 @@ usage: grammar_file_path [source_file_path]
A <- 'hello' ^ 'world'
> peglint a.peg
a.peg:1:14: syntax error
a.peg:1:16: syntax error
```
```