CODEWITHSUNDEEP
syntaxidesyntax-errorvalidation
lcssanches
lcssanches

Reputation: 1014

Building a syntax checker

I am building a app like a compiler with my own script language. The user will enter the code and the output will be another app. So I need tell to user if some line is wrong and why it is.

But I don't know how to start.

I thought this: All lines will start with a keyword, except for those who start with an variable. So different that are wrong. So, I can calculate the next valid entries and check them.

Also, I thought that I can check each line, but it's complex because I can have this

var varName { /* ... */ };

Or

var varName {
/* ... */
};

Or Even

var varName
{
/* ... */
};

So why not remove the break-lines and check? Because I will lose the line number, which in this case is the most important. Maybe I'm going to create a map between the code with and without break-line.

But first I want to hear you, if you already has this experience or you have any idea.

Thanks

Upvotes: 3

Views: 1614

Answers (3)

SKi
SKi

Reputation: 8476

You should check tools like: lex, bison and yacc.

lex is lexical analyser generator. It generates a code, which could be used for breaking the script to tokens (like numbers, keywords and so on...).

bison and yacc are both parser generators. Both can be used for generating code for parsing your language (combining tokens to statements).

Just google tutorials for those tools.

Upvotes: 2

sunapi386
sunapi386

Reputation: 1357

It'll be fairly complicated to write your own language. But totally doable.

To able to recognize if a line is wrong, in the syntactical sense, you'd need to build a parser. The parser checks the context-free grammar for a correct derivation of a structure from its tokens.

First you need to tokenize the file, then reconstruct it into a parse tree (to check syntax).

I took a class in this, CS 241. There's a very nice set of course notes which this is all explained in detail. https://github.com/christhomson/lecture-notes/blob/master/cs241.pdf

Upvotes: 1

Grzegorz Krugły
Grzegorz Krugły

Reputation: 11

There are formal languages to describe syntax and semantics of the language and there are tools that will generate parsers out of these descriptions. I suggest reading on flex and bison for starters.

Upvotes: 1

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