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added @macroexpand #18660

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merged 8 commits into from
Sep 30, 2016
Merged

added @macroexpand #18660

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988f7a1
added @macroexpand
jw3126 Sep 24, 2016
bff375b
Update expr.jl
jw3126 Sep 24, 2016
0b2c3ca
added @macroexpand to rst
jw3126 Sep 24, 2016
2dfe407
fix
jw3126 Sep 25, 2016
691052d
fixup: improving docu and removing test/expr.jl
jw3126 Sep 29, 2016
ebe9b53
fixup
jw3126 Sep 29, 2016
c66c096
Update expr.jl
jw3126 Sep 29, 2016
f8157dc
Update choosetests.jl
jw3126 Sep 29, 2016
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1 change: 1 addition & 0 deletions base/exports.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -1052,6 +1052,7 @@ export
expand,
gensym,
macroexpand,
@macroexpand,
parse,

# help and reflection
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10 changes: 10 additions & 0 deletions base/expr.jl
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Expand Up @@ -61,6 +61,16 @@ Takes the expression `x` and returns an equivalent expression with all macros re
"""
macroexpand(x::ANY) = ccall(:jl_macroexpand, Any, (Any,), x)

"""
@macroexpand
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missing indent, and would have to be added to rst if this gets merged before #18588

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where do I have to add it to rst?

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done


Return equivalent expression with all macros removed (expanded).
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It should be documented that the expansion happens in the module where the @macroexpand macro is expanded (i.e. the same module if the expression is used directly) and not the current module when the returned code runs (which is the module if you call macroexpand) The difference is demonstrated below

julia> module M
       macro macroexpand(code)
           QuoteNode(macroexpand(code))
       end
       macro m()
           1
       end
       function f()
           (@macroexpand(@m), macroexpand(:(@m)))
       end
       end
M

julia> macro m()
           2
       end
@m (macro with 1 method)

julia> M.f()
(1,2)

This makes no difference when used in the REPL and as I said the current @macroexpand might be slightly better but this should still be documented.

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@jw3126 jw3126 Sep 26, 2016 •
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Can you give a usecase this would actually make a difference? And why is @macroexpand potentially better for interactive use?

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Can you give a usecase this would actually make a difference?

That's exactly what the code above is showing.

And why is @macroexpand potentially better for interactive use?

I said

This makes no difference when used in the REPL

"""
macro macroexpand(code)
code_expanded = macroexpand(code)
Expr(:quote, code_expanded)
end

## misc syntax ##

"""
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2 changes: 1 addition & 1 deletion test/choosetests.jl
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Expand Up @@ -33,7 +33,7 @@ function choosetests(choices = [])
"markdown", "base64", "serialize", "misc", "threads",
"enums", "cmdlineargs", "i18n", "workspace", "libdl", "int",
"checked", "intset", "floatfuncs", "compile", "parallel", "inline",
"boundscheck", "error", "ambiguous", "cartesian", "asmvariant"
"boundscheck", "error", "ambiguous", "cartesian", "asmvariant", "expr"
]

if Base.USE_GPL_LIBS
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18 changes: 18 additions & 0 deletions test/expr.jl
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@@ -0,0 +1,18 @@

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Why is this in a new file? This can probably go to parse or replutil or reflection.

# @macroexpand tests
macro seven_dollar(ex)
# simonbyrne example 18240
isa(ex,Expr) && ex.head == :$ ? 7 : ex
end

let
@test (@macroexpand @macroexpand x) == macroexpand(:(@macroexpand x))
@test (@macroexpand :(1+$y) ) == macroexpand(:( :(1+ $y)))
@test (@macroexpand @fastmath 1+2 ) == :(Base.FastMath.add_fast(1,2))
@test (@macroexpand @fastmath + ) == :(Base.FastMath.add_fast)
@test (@macroexpand @fastmath min(1) ) == :(Base.FastMath.min_fast(1))
@test (@macroexpand @doc "" f() = @x) == Expr(:error, UndefVarError(Symbol("@x")))
@test (@macroexpand @seven_dollar $bar) == 7
x = 2
@test (@macroexpand @seven_dollar 1+$x) == :(1 + 2)
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Is this actually the correct behaviour? Shouldn't it throw an error?

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You are right!

macro macroexpand(code)
    code_expanded = macroexpand(code)
    Expr(:quote, code_expanded)
end

code_expanded looks good the problem is the eval call on Expr(:quote, code_expanded) which does $ interpolation.

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So would the solution be to search and quote the dollars expressions in code_expanded?

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I'm honestly not sure. This stuff always makes my head hurt.

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I think correct behaviour would be not to throw an error but return something like
1 + $(Expr(:$, :x))

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Yeah my head hurts, too.

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Maybe it would be better to print the result, rather than return it, i.e. do:

macro macroprint(code)
    print(macroexpand(code))
end

After all, that's probably what you want in 99% of cases.

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@yuyichao yuyichao Sep 24, 2016 •
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👎 to print it.

macro macroexpand(code)
    QuoteNode(macroexpand(code))
end

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Is eval(QuoteNode(ex)) == ex for all expressions ex?

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It should be.

end