Re: Parsing if, while, for, etc

[Akim Demaille]

>>>>> "JB" == JB  <address@hidden> writes:

JB> Hey, thanks for the detail! Yeppers, I have Modern Compiler
JB> Implementation in C, but unfortunately I understand very little of
JB> it. It is written very poorly in my opinion. I still don't
JB> understand why textbook authors can't write in plain English so
JB> people can read and understand their books, instead of filling
JB> their books with unintelligible squiggles and marks that mean
JB> nothing. Why? Why not a book that people can actually read with
JB> clear, plain English text and clear diagrammes? Beats me.

I disagree with about all your points :)

JB> Why is GNU awk a good example? What is awk?

Use any search engine.

JB> Yes, intermediate representation is something I'm struggling with,
JB> but I am also struggling with how to build if, while, for
JB> etc. What are those bits beginning with '@'?

See the Bison documentation.

JB> WHILE_LOOP: WHILE expr DO stmt_list END WHILE ; { /* C code of
JB> some sort */ }

JB> In the part where the C code goes, if I was writing an interpreter
JB> and wanted to execute this straight away, could I just write:

JB> { while ($2) { $4; } }

JB> .... or am I missing something? What would $4 contain in this
JB> case? Would I need to pass it into a function I write myself to
JB> extract the individual statements, if any? Hmm...

I'm not sure you were writing `meta' stuff or real stuff.  Of course
you cannot mean to write

WHILE_LOOP: WHILE expr DO stmt_list END WHILE
    { while ($2) { $4; } }

since $2 and $4 are meaningful only when you run the parser generated
by Bison.  But as *pseudo* code, what your wrote is meaningful.


JB> Can you shed any light on this for me? I have tried reading the
JB> bison input file for gcc, but it is too advanced for me to break
JB> up into pieces and learn from. I looked for the functions the file
JB> referred to when it recognised something, but couldn't find them
JB> anywhere.

Sorry, but you'll have to give more details on your intentions.  And I
think you should look at awk.y in Gawk's package, you'll learn there.