Add syllable functions to pcgroup

Moved from the mjrodgers-OW_GModules branch.

src/Groups/pcgroup.jl

@@ -365,3 +365,28 @@ function pc_group(c::GAP_Collector)
  end
 end
 
+function Oscar.syllables(g::Union{PcGroupElem, SubPcGroupElem})
+ l = GAPWrap.ExtRepOfObj(GapObj(g))
+ @assert iseven(length(l))
+ return Pair{Int, ZZRingElem}[l[i-1] => l[i] for i = 2:2:length(l)]
+end
+
+# Convert syllables in canonical form into exponent vector
+#Thomas
+function exponent_vector(sylls::Vector{Pair{Int64, ZZRingElem}}, n)
+ res = zeros(ZZRingElem, n)
+ for pair in sylls
+ @assert res[pair.first] == 0 #just to make sure 
+ res[pair.first] = pair.second
+ end
+ return res
+end
+
+# Convert syllables in canonical form into group element
+#Thomas
+function (G::PcGroup)(sylls::Vector{Pair{Int64, ZZRingElem}})
+ e = exponent_vector(sylls, ngens(G))
+ pcgs = Oscar.GAPWrap.FamilyPcgs(GapObj(G))
+ x = Oscar.GAPWrap.PcElementByExponentsNC(pcgs, GapObj(e, true))
+ return Oscar.group_element(G, x)
+end