A simple library to call Alloy given a specification.

Please see the README on GitHub at https://github.com/marcellussiegburg/call-alloy#readme

call-alloy

This is a simple library to call Alloy given a specification. This package installs a simple Java Library to make an API call to the Alloy Library. Alloy is installed (as JAR file) alongside this library as well.

Requirements

• Java Runtime Environment: There is currently no warning if you have not set up any Java Runtime Environment. However, you will get runtime errors if it is not available when a call to Alloy happens. If you want to force a check, perform the test cases.

Please note

The Java interface to get Alloy instances as well as the Alloy Jar file are installed together with this library using usual cabal means (data directory).

The library in action

This is a basic description on how to use the library.

A specification example

Consider this Alloy specification of a simple Graph:

abstract sig Node {
  flow : Node -> lone Int,
  stored : one Int
} {
  stored >= 0
  all n : Node | some flow[n] implies flow[n] >= 0
  no flow[this]
}

fun currentFlow(x, y : one Node) : Int {
  let s = x.stored, f = x.flow[y] | s < f implies s else f
}

pred withFlow[x, y : one Node] {
  currentFlow[x, y] > 0
}

pred show {}

run withFlow for 3 Int, 2 Node

The graph is consisting of Nodes, which might have some goods stored and may deliver them to other Nodes (via flow). Nodes do not have flow to themselves. The currentFlow is the minimum between the flow from the starting Node to the end Node and the currently stored goods at the starting Node (note: intermediate Nodes are not allowed). We call two Nodes x and y withFlow if currentFlow from x to y is greater than 0. We restrict our search to 3-Bit signed Int values and 2Nodes.

An instance example

Calling Alloy using getInstances and the above program could return the following (abbreviated) instance:

[(Signature {
    scope = Nothing,
    sigName = "$withFlow_x"
    },
  Entry {
    annotation = Just Skolem,
    relation = fromList [
      ("",Single (fromList [Object {objSig = "Node", identifier = 1}]))
      ]
    }),
 (Signature {
    scope = Nothing,
    sigName = "$withFlow_y"
    },
  Entry {
    annotation = Just Skolem,
    relation = fromList [
      ("",Single (fromList [Object {objSig = "Node", identifier = 0}]))
      ]
    }),
 ...
 (Signature {
    scope = Just "this",
    sigName = "Node"
    },
  Entry {
    annotation = Nothing,
    relation = fromList [
      ("",Single (fromList [
        Object {objSig = "Node", identifier = 0},
        Object {objSig = "Node", identifier = 1}
        ])),
      ("flow",Triple (fromList [
        (Object {objSig = "Node", identifier = 0},Object {objSig = "Node", identifier = 1},NumberObject {number = 0}),
        (Object {objSig = "Node", identifier = 1},Object {objSig = "Node", identifier = 0},NumberObject {number = 3})
        ])),
      ("stored",Double (fromList [
        (Object {objSig = "Node", identifier = 0},NumberObject {number = 0}),
        (Object {objSig = "Node", identifier = 1},NumberObject {number = 1})
        ]))
      ]
    })
 ]

A retrieval example

Using this library we may retrieve returned signature values using lookupSig, then query parameter variables of the queried predicate using unscoped, and query signature sets and relations using getSingleAs, getDoubleAs, and getTripleAs.

The following Code might for instance be used for the graph example:

newtype Node = Node Int deriving (Eq, Show, Ord)

instanceToNames
  :: AlloyInstance
  -> Either String (Set Node, Set (Node, Int), Set (Node, Node, Int), Set (Node), Set (Node))
instanceToNames insta = do
  let node :: String -> Int -> Either String Node
      node = object "Node" Node
  n     <- lookupSig (scoped "this" "Node") insta
  nodes <- getSingleAs "" node n
  store <- getDoubleAs "stored" node int n
  flow  <- getTripleAs "flow" node node int n
  x     <- lookupSig (unscoped "$withFlow_x") insta >>= getSingleAs "" node
  y     <- lookupSig (unscoped "$withFlow_y") insta >>= getSingleAs "" node
  return (nodes, store, flow, x, y)

Calling instanceToNames on the above instance would result in the following expression:

Right (
  fromList [Node 0,Node 1],
  fromList [(Node 0,0),(Node 1,1)],
  fromList [(Node 0,Node 1,0),(Node 1,Node 0,3)],
  fromList [Node 1],
  fromList [Node 0]
  )