Mike Gunter wrote: > However, forward branches make things harder. I'd like to be able to > write something along the lines of:
[snip] > but it's not clear to me how to implement it. I'd be willing to > accept a somewhat less clean version (for instance, with more > cumbersome forward references.) > > Any help would be greatly appreciated. What is the structure of the data which is produced by the assembler? If it roughly corresponds to conventional machine code (e.g. a list of opcodes with parameters), then you can use similar techniques to those used by a "real" assembler. If you are assembling into a list, the simplest approach is to perform the assembly phase twice. The first phase generates the list of label/address pairs. The second phase, which has the complete list of label addresses available, performs the complete assembly process. Both phases could use identical code; you just need to ensure that the first phase can assemble a branch instruction for which the label is unknown. Alternatively, you could perform one pass plus a post-processing phase which "fixes" any forward references. This would require either that you can store a label in an assembled branch instructions in place of an actual address, or that you generate a list incomplete branch instructions so that you can go back and fix them. OTOH, if you're actually interpreting the "assembly language" directly, then a forward branch would have to store the label in a "variable" to indicates that instructions are just to be skipped until that label is reached. -- Glynn Clements <[EMAIL PROTECTED]> _______________________________________________ Haskell mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell
