Not exactly. Line 30 has a VAL f$ which effectively evaluates the function. So VAL "3*x^2 + 5" will evaluate for every value of x variable.

Most BASIC implementations (e.g. C64) returned 0.

That's exactly the impression I got! Thank you for sharing! :-)

I went to the theater to see TRON when I was 10 (ZX Spectrum arrived 3 years later, for Christmas). I liked TRON Legacy, but the film had lot of unexplored possibilities the lazy scripters could worked out more. :-P Anyway, after seen it I asked myself whether I will see another TRON sequel in the future or not... and how could it be.

Hmmm. Lines 40/50 overlapped because of the "<" operator and sucking HTML. They must read:
40 IF y >= 0 and y < 175 THEN PLOT (x + 127), y
50 NEXT x

ZX Spectrum BASIC was much superior to C64 or MSX one (though slower). Try this in C4/MSX:

10 CLS: INPUT "Type in a function (e.g. x^3). f(x)="; f$
20 PRINT "Your function:"; f$
30 FOR x = -127 TO 127: LET y = 85 + VAL f$
40 IF y > 0 AND y 50 NEXT x

This is a simple general function plotter, which plots the function given by the user (allows SIN/COS/EXP etc. etc). Now try that in C64 BASIC. :P Challenge!
C64 was a nice machine, but I learned a lot of math and programming thanks to my Speccy :P

There are many free Web OS (as I understand them) out there. For example, EyeOS at http://eyeos.org/en or this other: http://www.oos.cc/login.html YouOS https://www.youos.com/ (now closed :( ) and one from the MIT whose URL I can't recall now... These project are 2 or more years old. If the new Web OS is just this old concept, I think like they're just shouting buzzword (again).