julia> versioninfo()
Julia Version 1.0.1
Commit 0d713926f8 (2018-09-29 19:05 UTC)
Platform Info:
  OS: macOS (x86_64-apple-darwin14.5.0)
  CPU: Intel(R) Core(TM) i5-5287U CPU @ 2.90GHz
  WORD_SIZE: 64
  LIBM: libopenlibm
  LLVM: libLLVM-6.0.0 (ORCJIT, broadwell)
Environment:
  JULIA_NUM_THREADS = 2

julia> @vars a
(a,)

julia> a + true
ERROR: MethodError: promote_rule(::Type{Bool}, ::Type{Basic}) is ambiguous. Candidates:
  promote_rule(::Type{S}, ::Type{Basic}) where S<:Number in SymEngine at /Users/felipeavba/.julia/packages/SymEngine/sh7Yz/src/types.jl:97
  promote_rule(::Type{Bool}, ::Type{T}) where T<:Number in Base at bool.jl:4
Possible fix, define
  promote_rule(::Type{Bool}, ::Type{Basic})
Stacktrace:
 [1] promote_type at ./promotion.jl:221 [inlined]
 [2] _promote at ./promotion.jl:260 [inlined]
 [3] promote at ./promotion.jl:284 [inlined]
 [4] +(::Basic, ::Bool) at ./promotion.jl:313
 [5] top-level scope at none:0