Guidelines on syntax checking for macros

CameronBieganek · April 20, 2024, 12:40am

Currently I’m developing a few macros that behave a bit like language keywords (there is no public non-macro interface). I’ve been leaning towards aggressively checking the syntax/expressions that the user provides and throwing informative errors if they don’t use the right syntax.

Is this a reasonable approach? Are there any guidelines on whether one should or should not do verification of the input syntax in macros?

Perhaps if you’re writing a macro that does some fairly simple syntax transformations and then calls a function that is part of your public API, then maybe it’s reasonable to just assume correct syntax and let the public function throw errors on bad input? (Which is not my situation—as mentioned above my macros behave more like language keywords.)

odow · April 20, 2024, 4:51am

Aggressively validate input syntax. You may find reading the various JuMP macros helpful:

github.com

jump-dev/JuMP.jl/blob/master/src/macros/@variable.jl

#  Copyright 2017, Iain Dunning, Joey Huchette, Miles Lubin, and contributors
#  This Source Code Form is subject to the terms of the Mozilla Public
#  License, v. 2.0. If a copy of the MPL was not distributed with this
#  file, You can obtain one at https://mozilla.org/MPL/2.0/.

"""
    @variable(model, expr, args..., kw_args...)

Add a variable to the model `model` described by the expression `expr`, the
positional arguments `args` and the keyword arguments `kw_args`.

## Anonymous and named variables

`expr` must be one of the forms:

 * Omitted, like `@variable(model)`, which creates an anonymous variable
 * A single symbol like `@variable(model, x)`
 * A container expression like `@variable(model, x[i=1:3])`
 * An anonymous container expression like `@variable(model, [i=1:3])`

This file has been truncated. show original

github.com

jump-dev/JuMP.jl/blob/509ab616192bc90891c329010e2205f414c8cf94/src/Containers/macro.jl#L625


      
          julia> Containers.@container([i = 1:3, j = 1:3; i <= j], i + j)
          SparseAxisArray{Int64, 2, Tuple{Int64, Int64}} with 6 entries:
            [1, 1]  =  2
            [1, 2]  =  3
            [1, 3]  =  4
            [2, 2]  =  4
            [2, 3]  =  5
            [3, 3]  =  6
          ```
          """
          macro container(input_args...)
              args, kwargs = parse_macro_arguments(
                  error,
                  input_args;
                  num_positional_args = 2,
                  valid_kwargs = [:container],
              )
              name, index_vars, indices = parse_ref_sets(error, args[1])
              code = container_code(index_vars, indices, esc(args[2]), kwargs)
              if name === nothing
                  return code