# Simple Lexer

Simple Lexer is a simple lexer that translate a lexer rule file into a target programming language source code.

Currently, this project aims on supporting following platform/languages:

|Language| Version| Platform|
|--------|--------|---------            |
|C       |  99    | Win32, POSIX, ESP32                          |
|C#      |  9.0   | .netstandard2.1(all possible target platform, including Unity)|

## Lexer Rule File Format

```
rule:

<Tag> <MatchingPattern>
<Tag> <MatchingPattern>
...

mapping:

<Id> <Tag>

code:

%<lang1>%

%post_processor
...
code for lang2
...
post_processor%

%variables
variables in post_processor accessible scope like state management.
variables%


%<lang2>%
%post_processor
...
code for lang2
...
post_processor%

%variables
variables in post_processor accessible scope like state management.
variables%

```

Code for each languages are for post-processing purpose only.
Code inside post_processor will directly replace staff inside `slex_post_process(...)` for each language.

## Usage

```
slex [options] <input_file> [options]

input file usually ends with `.slex`

Options:

-o <output> output file/output folder
-l <language> specify target language, e.g: c, c#, csharp
-h <header> output header file (will separate output implementation and definitions when language is c or c++. Note: c++ is currently not supported.)
-ns <namespace> specify namespace (supported languages only). Default is `slex_generated`, `SLexGenerated`, `io.creeperlv.slex.generated` for applicable language.
-class <class_name> specify class name (supported languages only). Default is `slexer`, `SLexer`.
-prefix <function_prefix> specify prefix for functions. Default is `slex_` for languages does not support namespace/class, `` (empty string) for languages support namespace/class.
-data_type <data_type_name> specify the name of the segment data type. Different language have different default value:

```
## Data Type Name Table

|Language| Type Name|
| - | - |
| C | slex_segment  |
| C# | Segment		|

### Generated Lexer

All usages here uses default settings

#### C99

Default options:

```
 -prefix slex_ -data_type slex_segment
```

Usage sample:
```
void slex_sample(FILE* f, char* file_name){
	
	struct slex_segment* head;
	const char* str="<some_inputs>";
	if(slex_file(f, file_name, &head)){
		//Success
	}
	slex_free(head);
	if(slex_cstr(str, &head)){
		//Success
	}
	slex_free(head);
}
```
API and defined data types:
```c
typedef struct slex_segment{
	char* head;
	int64_t length;
	char* file_name;
	int64_t line;
	int64_t col;
    enmu slex_segment_tag;
    enmu slex_segment_id;
	struct slex_segment prev;
	struct slex_segment next;
} slex_segment;

typedef enmu slex_segment_tag{
    <generated from rule file>
}slex_segment_tag;
typedef enmu slex_segment_id{
    default, <generated from rule file>
}slex_segment_id;
char slex_file(FILE* f, char* file_name, slex_segment** head);
char slex_cstr(char* input, char* file_name, slex_segment** head);
char slex_free(slex_segment* head);
```

`slex_post_process` definition:

```c

typedef enum slex_post_process_result{
    slex_continue,
    slex_skip,
    slex_continue_with_output,
}slex_post_process_result;
slex_post_process_result slex_post_process(slex_segment* input, slex_segment** output);
```


#### C#
Default options:

```
 -ns SLexGenerated -class SLexer -data_type Segment -prefix ""
 ```
 
##### APIs:
```
namesapce SLexGenerated{
	public class SLexer{
			public bool SLex(FileInfo inputFile, out Segment Head);
			public bool SLex(Stream inputStream, out Segment Head);
			public bool SLex(string inputContent, out Segment Head);
            private PostProcessResult slex_post_process(Segment Input,out Segment Output){
                //Default implementation:
                Output=Input;
                return PostProcessResult.Continue;
            }
	}
    public enum PostProcessResult{
        Continue,
        Skip,
        ContinueWithOutput
    }
	public class Segment{
		public string Content;
		public string FileName;
		public Segment? Prev;
		public Segment? Next;
		public long Line;
		public long Column;
	}
}
```