add SLPolyRing(r, :x => 1:3, :y => 2:4) etc.

src/slpolys.jl

@@ -13,6 +13,11 @@ SLPolyRing(r::Ring, s::Union{AbstractVector{<:AbstractString},
 
 SLPolyRing(r::Ring, n::Integer) = SLPolyRing(r, [Symbol("x$i") for i=1:n])
 
+# cf. mpoly.jl in Oscar
+SLPolyRing(r::Ring, v::Pair{<:Union{String,Symbol},
+                            <:AbstractVector{<:Integer}}...) =
+    SLPolyRing(r, [Symbol(s, n) for (s, ns) in v for n in ns])
+
 base_ring(S::SLPolyRing) = S.base_ring
 
 symbols(S::SLPolyRing) = S.S
@@ -38,6 +43,26 @@ function PolynomialRing(R::Ring, s)
     S, gens(S)
 end
 
+function PolynomialRing(R::Ring, v::Pair{<:Union{String,Symbol},
+                                         <:AbstractVector{<:Integer}}...)
+    S = SLPolyRing(R, v...)
+
+    # TODO: enable on Julia 1.5 (required for init keyword)
+    # rs = Iterators.accumulate(v; init=0:0) do x, a
+    #     last(x)+1:last(x)+length(a[2])
+    # end
+    rs = []
+    prev = 0
+    for a in v
+        newprev = prev+length(a[2])
+        push!(rs, prev+1:newprev)
+        prev = newprev
+    end
+
+    gs = gens(S)
+    S, (gs[r] for r in rs)...
+end
+
 Base.one(S::SLPolyRing) = S(one(base_ring(S)))
 Base.zero(S::SLPolyRing) = S()
 

test/straightline.jl

@@ -265,6 +265,18 @@ end
     @test length(X) == 2
     @test string.(X) == ["x1", "x2"]
 
+    S5 = SLPolyRing(zz, :x => 1:3, :y => [2, 4])
+    @test S5 isa SLPolyRing{Int}
+    XS = gens(S5)
+    @test string.(XS) == ["x1", "x2", "x3", "y2", "y4"]
+
+    S5, X, Y = SL.PolynomialRing(zz, :x => 1:3, "y" => [2, 4])
+    @test S5 isa SLPolyRing{Int}
+    XS = gens(S5)
+    @test string.(XS) == ["x1", "x2", "x3", "y2", "y4"]
+    @test X == XS[1:3]
+    @test Y == XS[4:5]
+
     s1 = one(S)
     @test s1 == 1
     @test s1 isa SLPoly{Int}