73 lines
2.1 KiB
Markdown
73 lines
2.1 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.We really need your support!
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# Why Writing Nasal Interpreter
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Nasal is a script language first used in Flightgear.
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But in last summer holiday, members in FGPRC told me that it is hard to debug with nasal-console in Flightgear, especially when checking syntax error.
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So i tried to write a new interpreter to help them checking syntax error and even, runtime error.
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I wrote the lexer, parser and runtime(nasal virtual machine/ast-runtime virtual machine) to help checking errors.
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They found it easier for them to check errors before copying nasal-codes in nasal-console in Flightgear to test.
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# Lexical Analysis
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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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# Parser
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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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## In __version 3.0__
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I refactored parser and make it easier to maintain.
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the EBNF is also refactored.
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# Abstract Syntax Tree
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In __version 1.2__ the ast has been completed.
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In __version 3.0__ the ast is refactored and is now easier to read and maintain.
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# Version 2.0
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a completed ast-interpreter with unfinished lib functions.
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# Version 3.0
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ast-interpreter uses new techniques so it can run codes more efficiently.
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byte-code-interpreter is in progress(i need a lot of time to learn that :( ).
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