On Mon, 21 Oct 2013 21:24:38 -0700, Mark Janssen wrote: >> A language specification in BNF is just syntax. It doesn't say anything >> about semantics. So how could this be used to produce executable C code >> for a program? BNF is used to produce parsers. But a parser isn't >> sufficient. > > A C program is just syntax also. How does the compiler generate > executable machine code? Extrapolate into a Python front-end to C.
Like every other language, C programs are certainly not *just* syntax. Here is some syntax: &foo bar^ := What machine code should be produced? Right now, you should be saying "How the hell do I know? What does that line of code *do*???" and you would be right to ask that question. Syntax on its own doesn't mean anything. You also need to know the *semantics* of the code, in other words, *what it means*. That knowledge is inherent to the compiler: a C compiler "understands" what C code means, a Pascal compiler "understands" Pascal code, a Forth compiler "understands" Forth. Merely parsing code doesn't capture that understanding. Parsing a line like "foo <= bar" will give you something like this: NAME "foo" OPERATOR "<=" NAME "bar" END_LINE What does the operator "<=" actually do? What does "foo" represent? Is it a variable, a constant, a global, a local, something else? What are the rules for deciding whether a variable is in the local scope, a global scope, or something else? Does the language even have scopes? -- Steven -- https://mail.python.org/mailman/listinfo/python-list
