Implement Epoch ranges

src/Epochs.jl

@@ -195,6 +195,8 @@ function Epoch{S2}(ep::Epoch{S1}) where {S1, S2}
     Epoch{S2}(ep.epoch, ep.offset, tai_offset(S2, ep))
 end
 
+Epoch{S, T}(ep::Epoch{S, T}) where {S, T} = ep
+
 function isapprox(a::Epoch, b::Epoch)
     a.epoch == b.epoch && a.offset ≈ b.offset
 end
@@ -221,6 +223,7 @@ for scale in TimeScales.ACRONYMS
 end
 
 include("leapseconds.jl")
+include("range.jl")
 
 const JULIAN_EPOCH = TTEpoch(AstroDates.JULIAN_EPOCH, AstroDates.H12)
 const J2000_EPOCH = TTEpoch(AstroDates.J2000_EPOCH, AstroDates.H12)

src/Periods.jl

@@ -1,10 +1,10 @@
 module Periods
 
-import Base: *, /, get, isapprox, show
+import Base: -, *, /, get, isapprox, show
 
 export TimeUnit, Second, Minute, Hour, Day, Year, Century,
     seconds, minutes, hours, days, years, centuries,
-    Period, *, /, get,
+    Period, -, *, /, get,
     SECONDS_PER_MINUTE,
     SECONDS_PER_HOUR,
     SECONDS_PER_DAY,
@@ -85,6 +85,7 @@ show(io::IO, p::Period{Century}) = print(io, "$(get(p)) centuries")
 
 (*)(Δt::T, ::U) where {T<:Number, U<:TimeUnit} = Period{U}(Δt)
 
+(-)(p::Period) = Period{p.unit}(-p.Δt)
 (*)(x::T, p::Period) where {T<:Number} = Period{p.unit}(p.Δt * x)
 (*)(p::Period, x::T) where {T<:Number} = Period{p.unit}(p.Δt * x)
 (/)(x::T, p::Period) where {T<:Number} = Period{p.unit}(x / p.Δ)

src/range.jl

@@ -0,0 +1,12 @@
+import Base: (:)
+
+(:)(start::Epoch{S}, stop::Epoch{S}) where {S} = (:)(start, 1.0days, stop)
+
+function (:)(start::Epoch{S}, step::Period, stop::Epoch{S}) where S
+    step = seconds(step)
+    step = start < stop ? step : -step
+    StepRangeLen(start, step, floor(Int, get(stop-start)/get(step))+1)
+end
+
+Base.step(r::StepRangeLen{T}) where {T<:Epoch} = r.step
+