89 lines
2.2 KiB
Markdown
89 lines
2.2 KiB
Markdown
# Nasal Interpreter
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[](http://wiki.flightgear.org/File:Nasallogo3.png)
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# Nasal script language
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[Nasal](http://wiki.flightgear.org/Nasal_scripting_language) is a script language that used in [FlightGear](https://www.flightgear.org/).
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There is a Nasal console in FlightGear but sometimes it is not so easy for every developer to use.
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So this is an interpreter for Nasal written by C++.
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The interpreter is still in development.Anyone who interested in this could also join us!
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# Lexical Analysis
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What do it's outputs look like?
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> ( identifier | start )
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> ( operator | ; )
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> ( reserve word | print )
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> ( operator | ( )
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> ( string | Engine started )
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> ( operator | ) )
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This is what it outputs.
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And the flow chart of lexer is here:
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[](https://github.com/ValKmjolnir/Nasal-Interpreter/blob/master/pic/nasal_lexer.png)
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# Push down automata
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After many times of failure,i finally try to use PDA to do the parse work.
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But something occurred,so i finally didn't make it.However you can still see this LL(1) and LR(0) parser in __version 0.7 & 0.9__ .
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# Parser
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The parser can recognize some basic elements in resource program.
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In __version 1.1__ you can use the fully-functional parser.
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But there are still some differences such as:
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```javascript
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(var a,b,c)=(1,2,3);
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var (r,g,b)=color;
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(a,b)=(b,a);
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```
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etc. cannot be recognized.
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And each statement must have a ';' after it or you will be informed with __'error: expect a ';''__ .
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In __version 2.0__ these problems have been solved.
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In __version 2.0__
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```javascript
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(var a,b,c)=(1,2,3);
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var (r,g,b)=color;
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```
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These two types of statements are both definition_expr.
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```javascript
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(a,b,c)=(1,2,3);
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(a,b)=(b,a);
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```
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This type of statement is multi_assignment.
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__And to check if an expr in '(' ')' is multi_scalar or multi_id__
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__i used bool nasal_parse::check_multi_scalar() and bool nasal_parse::check_multi_assignment()__
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# Abstract Syntax Tree
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In __version 1.2__ the ast has been completed.
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# Version 2.0
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a completed ast-interpreter with unfinished lib functions.
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a new byte code interpreter is in progress(version 3.0).
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