add chain

Author: ChrisRackauckas

src/utils.jl

@@ -111,3 +111,64 @@ function recursive_mean{T<:AbstractArray}(matarr::Matrix{T},region=0)
     return recursive_mean(matarr',1)
   end
 end
+
+
+# From Iterators.jl. Moved here since Iterators.jl is not precompile safe anymore.
+
+# Concatenate the output of n iterators
+immutable Chain{T<:Tuple}
+    xss::T
+end
+
+# iteratorsize method defined at bottom because of how @generated functions work in 0.6 now
+
+"""
+    chain(xs...)
+
+Iterate through any number of iterators in sequence.
+```jldoctest
+julia> for i in chain(1:3, ['a', 'b', 'c'])
+           @show i
+       end
+i = 1
+i = 2
+i = 3
+i = 'a'
+i = 'b'
+i = 'c'
+```
+"""
+chain(xss...) = Chain(xss)
+
+Base.length(it::Chain{Tuple{}}) = 0
+Base.length(it::Chain) = sum(length, it.xss)
+
+Base.eltype{T}(::Type{Chain{T}}) = typejoin([eltype(t) for t in T.parameters]...)
+
+function Base.start(it::Chain)
+    i = 1
+    xs_state = nothing
+    while i <= length(it.xss)
+        xs_state = start(it.xss[i])
+        if !done(it.xss[i], xs_state)
+            break
+        end
+        i += 1
+    end
+    return i, xs_state
+end
+
+function Base.next(it::Chain, state)
+    i, xs_state = state
+    v, xs_state = next(it.xss[i], xs_state)
+    while done(it.xss[i], xs_state)
+        i += 1
+        if i > length(it.xss)
+            break
+        end
+        xs_state = start(it.xss[i])
+    end
+    return v, (i, xs_state)
+end
+
+Base.done(it::Chain, state) = state[1] > length(it.xss)