Overloading ≫ yields ERROR: TypeError: non-boolean used in boolean context

General Usage
1

Can anyone help why this weird error happens? (working on julia 1.6.1)

julia> a ≫  b = a + b
≫ (generic function with 1 method)

julia> (1 ≫  2) ≫  3
6

julia> 1 ≫  (2 ≫  3)
6

julia> 1 ≫  2 ≫  3
ERROR: TypeError: non-boolean (Int64) used in boolean context
Stacktrace:
 [1] top-level scope
   @ REPL[2]:1

Of course for me it would be awesome to just not having the error, but I guess that is not possible. Hence does someone know a similar unicode operator which does not yield this error?

2

Try

julia> Meta.@lower 1 ≫ 2 ≫ 3
:($(Expr(:thunk, CodeInfo(
    @ none within `top-level scope'
1 ─ %1 = 1 ≫ 2
└──      goto #3 if not %1
2 ─ %3 = 2 ≫ 3
└──      return %3
3 ─      return false
))))

I have no idea why it lowers to a conditional go to based on the result of 1 ≫ 2. With brackets it works though.

julia> (1 ≫ 2) ≫ 3
6

julia> 1 ≫ (2 ≫ 3)
6
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3

thank you for the lowering hint, I goes it is because this operator has the name “greater greater” and someone put “greater” comparison semantics onto it

a bit unfortunate as I wanted to use it for monad composition, where this unicode is quite commonly used as an operator

4

This is to support chaining of comparisons. See also this issue. As noted there you’d probably have to use a macro to work around the lowering.

2 Likes