This seems to work if the category is defined in the same source file (i.e. same section in MathAction). The code is based on the Spad version SandBox Category of Graphs in Spad

#pile
#include "axiom.as"
--
-- First we define the general category of graphs.
--
GraphCategory(nodes:Type, edges:Type): Category == with
  source:edges->nodes
  target:edges->nodes
--
-- Now we define finite graphs as follows:
--
edges ==> Record(source:nodes,target:nodes)
FiniteGraph(nodes: BasicType):GraphCategory(nodes,edges)
  with
    new: %
    addNode: (%,List nodes) -> List nodes
    addNode: (%,nodes) -> List nodes
    addEdge: (%,nodes,nodes) -> edges
    edgeList: (%) -> List edges
    nodeList: (%) -> List nodes

  == add
    import from NonNegativeInteger

    Rep == Record(node: List nodes, edge: List edges)

    new:% == 
      n:List(nodes):=[]
      e:List(edges):=[]
      per([n,e]$Rep)

    addNode(g:%,n:nodes):List nodes == addNode(g,[n])

    addNode(g:%,n:List nodes):List nodes ==
      G:Rep:=g pretend Rep;
      if #G.node=0 then
        G.node:=n
      else
        concat!(G.node,n)
      n

    addEdge(g:%,source:nodes,target:nodes):edges ==
      G:Rep:=g pretend Rep;
      if #G.edge=0 then
        G.edge:=[[source,target]$edges]
      else
        concat!(G.edge,[[source,target]$edges])
      [source,target]$edges

    edgeList(g:%):List edges ==
      G:Rep:=g pretend Rep;
      G.edge

    nodeList(g:%):List nodes ==
      G:Rep:=g pretend Rep;
      G.node

    source(ed:edges):nodes == ed.source
    target(ed:edges):nodes == ed.target

   Compiling FriCAS source code from file 
      /var/zope2/var/LatexWiki/1676669208528368195-25px001.as using 
      AXIOM-XL compiler and options 
-O -Fasy -Fao -Flsp -laxiom -Mno-AXL_W_WillObsolete -DAxiom -Y $AXIOM/algebra
      Use the system command )set compiler args to change these 
      options.
#1 (Warning) Deprecated message prefix: use `ALDOR_' instead of `_AXL'
   Compiling Lisp source code from file 
      ./1676669208528368195-25px001.lsp
   Issuing )library command for 1676669208528368195-25px001
   Reading /var/zope2/var/LatexWiki/1676669208528368195-25px001.asy
   FiniteGraph is now explicitly exposed in frame initial 
   FiniteGraph will be automatically loaded when needed from 
      /var/zope2/var/LatexWiki/1676669208528368195-25px001
   GraphCategory is now explicitly exposed in frame initial 
   GraphCategory will be automatically loaded when needed from 
      /var/zope2/var/LatexWiki/1676669208528368195-25px001

)sh FiniteGraph

 FiniteGraph nodes: BasicType  is a domain constructor
 Abbreviation for FiniteGraph is FINITEG
 This constructor is exposed in this frame.
 Issue )edit 1676669208528368195-25px001.as to see algebra source code for FINITEG 

------------------------------- Operations --------------------------------
 addNode : (%,nodes) -> List nodes     new : () -> %
 nodeList : % -> List nodes
 addEdge : (%,nodes,nodes) -> Record(source: nodes,target: nodes)
 addNode : (%,List nodes) -> List nodes
 edgeList : % -> List Record(source: nodes,target: nodes)
 source : Record(source: nodes,target: nodes) -> nodes
 target : Record(source: nodes,target: nodes) -> nodes

Example 1: create a simple finite graph:

g:FiniteGraph(INT)

g:=new()

 LISP output:
()

addNode(g,1)

(1)

addNode(g,2)

(2)

e:=addEdge(g,1,2)

(3)

source(e)$FiniteGraph(INT)

(4)

edgeList(g)

(5)

nodeList(g)

(6)