2014-04-13

Bison

Today I decided to bite something of Bison. In my far past I had already experimented (though in a strong yacc fashion) with it, and by this I mean I have read few quick and simple tutorials — nothing more than the omnipresent infix calculator with frills, which by the way is also the main example in the manual, with enhancements found in mfcalc (hopefully updated for the future). To me the matter (using the tool as well as understanding bits of its inner working) is vast, deep and really interesting, but this is also the reason why I was always pushed towards stack-based languages in my experimenting with this world. Stack-based languages can polish complexity, largely undesidered in toy languages. But in the very same time it makes these toy languages almost alien. Stack-based or not, beyond a point a computer language can't miss a tool like Bison, unless you want to make a lot of craft work by yourself — there could be good reasons to do so, but I can't imagine one that fits the world of a toy language.

So, maybe only to make a noise and a vibration here and there, here's the result and, ladies and gentlemen, it is … hold on tight … the omnipresent basic infix calculator! More or less. In fact, you can assign the result of an expression to a symbol, and use it later. The lexical scanner reads only from standard input, and … again hold on tight … you can write 0.5a instead of 0.5*a! I admit it, MetaFONT book was very influential over me, and so it was the MetaFONT language, which is by heart the only language I know that accepts a more natural notation for the multiplication. Think about it: 2a is a syntactic error in the vast majority of computer programming languages, at least among the most known. Even languages thought to handle math stuffs, I am thinking about R and Octave mainly (and also Maxima!), disallow this syntactic sugar. Nothing bad, but my very simply infix calculator makes it possible! This is an incredible feature!! (Irony here, of course).

If you are interested in these basic things for beginners and in a complete, messed up, but working example to play on, you can take it from a gist of mine. I have avoided full C++ style (other examples show the “driver class” C++ approach), just used C++ where it turns to be ease (STL map class, since for the rest C would have sufficed). The next idea will be similar, maybe, and it will be about lambda. Indeed, since easter is near, I have started these tests in order to build a toy tool to play with the Church lambda calculus (shame on you, it already exists cool Xyz you can use very profitably! Ok, that's not my plan to be profitable or whatever, I am just playing to keep my last two survivor neurons almost alive), but I suppose I will be late, as usual.

Final note: on gist, if you assign the name for the file, you can't use the highlight you want. So, since .yy is an unknown extension, it made me impossible to select C++ highlight. We live in a world dominated by extensions rather than by users' will.

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