Union problem in @capture

[aytekinar]

Hey! I was playing with the package and I spotted a problem while trying unions in @capture:

julia> using MacroTools

julia> versioninfo()
Julia Version 0.5.1
Commit 6445c82d00 (2017-03-05 13:25 UTC)
Platform Info:
  OS: Linux (x86_64-pc-linux-gnu)
  CPU: Intel(R) Core(TM) i7-3720QM CPU @ 2.60GHz
  WORD_SIZE: 64
  BLAS: libopenblas (NO_AFFINITY SANDYBRIDGE)
  LAPACK: liblapack
  LIBM: libm
  LLVM: libLLVM-3.7.1 (ORCJIT, ivybridge)

julia> macro m1(ex)
         @capture(ex, f_(args__) = body_ | function f_(args__) body_ end) || return ex
         @show f
         @show args
         @show body
         return ex
       end;

julia> macro m2(ex)
         @capture(ex, (f_{T_}|f_)(args__) = body_) || return ex
         @show f
         @show args
         @show body
         return ex
       end;

julia> macro m3(ex)
         @capture(ex, f_(args__) = body_) || @capture(ex, function f_(args__) body_ end) || return ex
         @show f
         @show args
         @show body
         return ex
       end;

julia> @m1 f(x) = 5x;
f = :f
args = Any[:x]
body = :(5x)

julia> @m1 function f(x) 5x end;
WARNING: Method definition f(Any) in module Main at REPL[6]:1 overwritten at REPL[7]:1.

julia> @m2 f(x) = 5x;
f = :f
args = Any[:x]
body = quote  # REPL[8], line 1:
    5x
end
WARNING: Method definition f(Any) in module Main at REPL[7]:1 overwritten at REPL[8]:1.

julia> @m3 f(x) = 5x;
f = :f
args = Any[:x]
body = quote  # REPL[9], line 1:
    5x
end
WARNING: Method definition f(Any) in module Main at REPL[8]:1 overwritten at REPL[9]:1.

julia> @m3 function f(x) 5x end;
f = :f
args = Any[:x]
body = quote  # REPL[10], line 1:
    5x
end
WARNING: Method definition f(Any) in module Main at REPL[9]:1 overwritten at REPL[10]:1.

Even though m1 and m2 are copies from README, they don't work properly. I hope I am not missing some stupid mistake while trying.

I'd appreciate if you could help. Thanks!

[aytekinar]

Same goes for the other example... When I change the order in (f_{T_}|f_)(args__) = body_, I have problems:

macro m2(ex)
  if @capture(ex, (f_{T_}|f_)(args__) = body_)
    @show f
    @show T
    @show args
    @show body
  end
  return ex
end

@m2 f(x) = 5x
@m2 f{T}(x::T) = 3x

macro m3(ex)
  if @capture(ex, (f_|f_{T_})(args__) = body_)
    @show f
    @show T
    @show args
    @show body
  end
  return ex
end

@m3 f(x) = 5x
@m3 f{T}(x::T) = 3x

macro m4(ex)
  if @capture(ex, ((f_)(args__) = body_) | ((f_{T_})(args__) = body))
    @show f
    @show T
    @show args
    @show body
  end
  return ex
end

@m4 f(x) = 5x
@m4 f{T}(x::T) = 3x

I cannot understand where I am doing a mistake. @m3 and @m4 do not work as intended.

[MikeInnes]

f_(args__) = body_ | function f_(args__) body_ end gets parsed as f_(args__) = (body_ | function f_(args__) body_ end) so that's causing one issue. The other stuff seems to be working for me:

julia> @capture(:(f(x) = 5x), (f_{T_}|f_)(args__) = body_)
true

julia> @capture(:(f{T}(x) = 5x), (f_{T_}|f_)(args__) = body_)
true

Are these definitely not working for you?

[aytekinar]

Your examples do work. Now I get the point --- sorry! In the very first version, as you have pointed out, lack of parenthesis was causing the headache. Then, when I change the order of (f_{T_}|f_) in your example to (f_|f_{T_}), the second one never gets triggered. Apparently, | in the macro is short circuit --- I had expected it to evaluate the right-hand side and give me the more specialized solution when one defines f{T}(x::T) = 3x in the expression. However, f_ catches them all.

Thanks for the answer!

[rjplevin]

I'm having a similar problem, but it shows up only if I restrict the type to match and use "|":

Main> ex = @MacroTools.q ext_var1[2010:2049, (US, CHI)] = name1
:(ext_var1[2010:2049, (US, CHI)] = name1)

# Works without specifying Symbol type
Main> @capture(ex, extvar_  = rvname_)
true

# Captures a symbol
Main> rvname
:name1

# Works with Symbol type without "|"
Main> @capture(ex, extvar_  = rvname_Symbol)
true

# Works with "|" without Symbol type
Main> @capture(ex, (extvar_ = rvname_) | (extvar_ += rvname_))
true

# Fails with "|" and Symbol type
Main> @capture(ex, (extvar_ = rvname_Symbol) | (extvar_ += rvname_))
false

# Just for completeness:
Main> @capture(ex, (extvar_ = rvname_) | (extvar_ += rvname_Symbol))
true

[cstjean]

Closing, as the original question was answered. Filed new issue in #180