newlines break `let`

[nsajko]

               _
   _       _ _(_)_     |  Documentation: https://docs.julialang.org
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  | | |_| | | | (_| |  |  Version 1.9.0-DEV.1171 (2022-08-23)
 _/ |\__'_|_|_|\__'_|  |  Commit df3da0582a7 (2 days old master)
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julia> let a = 1, b = 2  # works
         0
       end
0

julia> let  # works
         (a = 1,),
         (b = 2,)
         0
       end
0

julia> let  # works
         (a = 1),
         (b = 2)
         0
       end
0

julia> let  # fails
         a = 1,
         b = 2
         0
       end
ERROR: syntax: invalid assignment location "1" around REPL[4]:2
Stacktrace:
 [1] top-level scope
   @ REPL[4]:1

1.8.0 behaves the same.

[nsajko]

Perhaps related to #45719

[nsajko]

Also:

julia> let
         a = one(Int),
         b = zero(Int)
         5
       end
ERROR: BoundsError: attempt to access Int64 at index [2]
Stacktrace:
 [1] indexed_iterate(I::Int64, i::Int64, state::Nothing)
   @ Base ./tuple.jl:97
 [2] top-level scope
   @ REPL[7]:2

[nsajko]

The original post above was inaccurate with the "works" comment:

julia> let
         (a = 3),
         (b = 2)
         a * b
       end
ERROR: UndefVarError: a not defined
Stacktrace:
 [1] top-level scope
   @ REPL[1]:4

julia> let
         (a = 3,),
         (b = 2,)
         a * b
       end
ERROR: UndefVarError: a not defined
Stacktrace:
 [1] top-level scope
   @ REPL[2]:4

[nsajko]

Another, different, error message:

julia> let
         a = first((2,)),
         b = first((3,))
         a * b
       end
ERROR: syntax: malformed expression
Stacktrace:
 [1] top-level scope
   @ REPL[6]:1

[nsajko]

Can anyone think of a workaround?
The nicest thing I can think of is nesting lets, but that's not very nice at all.

[Keno]

julia> let # works
(a = 1,),
(b = 2,)
0
end
0

julia> let # works
(a = 1),
(b = 2)
0
end
0

These are let expressions without assignments and then a void construction of a tuple of named tuples, not let expressions.

[digital-carver]

julia> let  # fails
         a = 1,
         b = 2
         0
       end
ERROR: syntax: invalid assignment location "1" around REPL[4]:2

Similarly, this is a let expression without assignments, followed by a = 1, b = 2. Because this is not part of the let expression, it's seen as a = (1, b) = 2 i.e. an attempt to assign to (1, b), hence the error.

---

julia> let
         a = one(Int),
         b = zero(Int)
         5
       end
ERROR: BoundsError: attempt to access Int64 at index [2]

Same as above, except one(Int), b = zero(Int) has valid LHS locations, but zero(Int) on the RHS doesn't have two values to supply, so the the access fails there.

---

julia> let
         (a = 3),
         (b = 2)
         a * b
       end

Again, because the second and third lines are not part of the let expression, they're seen as the named tuple construction equivalent to

julia> (a = 3), (b = 2)
(a = 3, b = 2)

so a and b are keys in that named tuple and not being defined as variables.

---

julia> let
         a = first((2,)),
         b = first((3,))
         a * b
       end
ERROR: syntax: malformed expression

Equivalent to a = (first((2,)), b) = first((3,)), which also returns a malformed expression syntax error.

[nsajko]

Regarding workarounds, I guess that these two are equivalent:

julia> let a = 3,
           b = 4
         a + b
       end
7

julia> let a = 3, b = 4
         a + b
       end
7