Sorry, I'm not being as precise I should with language, but I did mean 'generate code to create a dictionary'. The macro exists already at the bottom of:
https://github.com/abeschneider/PEGParser.jl/blob/master/src/rules.jl On Sunday, March 22, 2015 at 11:27:54 PM UTC-4, Jameson wrote: > > My macro’s primary role is to create a dictionary mapping symbols to Nodes. > Each Node has an associated action (passed in with the curly braces). The > actions themselves are Exprs, which need to be encapsulated as functions. > > that’s not something a macro can do (directly). and it's also why a macro > is different from a function. > > specifically, a function’s purpose is to change one object into another > thing. on the other hand, a macro is for transforming code into more code. > so the return value from the macro isn’t a new object, but the code that > describes how to to make that new object. so for the example above, rather > than directly assigning expr.args[2] into rule.action, you would return > the equivalent expression (quote; rule.action = $(expr.args[2]); end) > that do that operation at runtime > > On Sun, Mar 22, 2015 at 11:01 PM Abe Schneider abe.schnei...@gmail.com > <http://mailto:abe.schnei...@gmail.com> wrote: > > Sorry, when I said AST, I meant the code that gets executed. A macro, at >> least the way I think about it, is inserting the resulting Expr into the >> main AST. >> >> My macro's primary role is to create a dictionary mapping symbols to >> `Node`s. Each Node has an associated action (passed in with the curly >> braces). The actions themselves are `Expr`s, which need to be encapsulated >> as functions. >> >> I was hoping initially that the `Expr` for the action could be converted >> inline with the creation of the `Node`, as it would save the need of a lot >> of book keeping. Thus, the: `rule.action = >> insert_action_expr(expr.args[2])`. >> >> Another solution might to do two passes, where in the second pass the >> rule's `Expr`s are converted. Unfortunately, that seems less elegant than >> being able to convert an `Expr` to a function. >> >> >> On Sunday, March 22, 2015 at 9:39:30 AM UTC-4, Toivo Henningsson wrote: >>> >>> Maybe there is a confusion of terms here? An Expr is the way to >>> represent an AST in Julia (some very simple ASTs are instead represented by >>> ints/floats/strings/symbols). So when you talk about inserting an Expr into >>> an AST it seems to me that all it means is to make an Expr where some >>> subtree is given by another Expr. >>> >>> Macros are really only a way to save typing. Consider a few cases: what >>> is the input AST, and what is the output AST that you want to generate in >>> each case. From there, you should be able to figure out how to write the >>> code that does the transformation. >> >> >
