Merge pull request #815 from null-a/fwd-sample-helpers

Add forward and forwardGuide helpers.

docs/functions/other.rst

@@ -41,6 +41,21 @@ Other
 
      marginalize(dist, 'a') // => Marginal with p(true) = 0.9, p(false) = 0.1
 
+.. js:function:: forward(model)
+
+   Evaluates function of zero arguments ``model``, ignoring any
+   :ref:`factor <factor>` statements.
+
+   Also see: :ref:`Forward Sampling <forward_sampling>`
+
+.. js:function:: forwardGuide(model)
+
+   Evaluates function of zero arguments ``model``, ignoring any
+   ``factor`` statements, and sampling from the :ref:`guide <guides>`
+   at each random choice.
+
+   Also see: :ref:`Forward Sampling <forward_sampling>`
+
 .. js:function:: mapObject(fn, obj)
 
    Returns the object obtained by mapping the function ``fn`` over the

docs/inference/methods.rst

@@ -343,6 +343,8 @@ Optimization
 
      Infer({method: 'optimize', samples: 100, steps: 100, model: model});
 
+.. _forward_sampling:
+
 Forward Sampling
 ----------------
 

src/inference/forwardSample.js

@@ -111,9 +111,20 @@ module.exports = function(env) {
     );
   }
 
+  function extractVal(k) {
+    return function(s, obj) {
+      return k(s, obj.val);
+    };
+  }
+
   return {
     ForwardSample: ForwardSample,
-    runForward: runForward
+    forward: function(s, k, a, model) {
+      return runForward(s, extractVal(k), a, model, false);
+    },
+    forwardGuide: function(s, k, a, model) {
+      return runForward(s, extractVal(k), a, model, true);
+    }
   };
 
 };

src/params/header.js

@@ -52,7 +52,7 @@ function defaultInit(mu, sigma) {
 
 module.exports = function(env) {
 
-  var runForward = require('../inference/forwardSample')(env).runForward;
+  var forward = require('../inference/forwardSample')(env).forward;
 
   var dimsForScalarParam = [1];
 
@@ -86,8 +86,7 @@ module.exports = function(env) {
         return init(s, k, a, dims);
       };
 
-      var next = function(k, ret) {
-        var initialVal = ret.val;
+      var next = function(k, initialVal) {
         params.create(name, initialVal);
         if (!_.isEqual(dims, initialVal.dims)) {
           var msg = 'The init function did not return a tensor with the expected shape.';
@@ -96,7 +95,7 @@ module.exports = function(env) {
         return finish(s);
       };
 
-      return runForward(s, next, a, initThunk);
+      return forward(s, next, a, initThunk);
     }
 
     function finish(s) {

tests/test-data/deterministic/expected/forward.json

@@ -0,0 +1,3 @@
+{
+  "result": [0, 1]
+}

tests/test-data/deterministic/models/forward.wppl

@@ -0,0 +1,11 @@
+var model = function() {
+  factor(0);
+  return sample(Delta({v: 0}), {guide() {
+    return Delta({v: 1});
+  }});
+};
+
+[
+  forward(model),
+  forwardGuide(model)
+];

tests/test-data/deterministic/models/observeParams.wppl

@@ -1,6 +1,6 @@
-sample(Infer({ method: 'forward', samples: 1, guide: true, model: function() {
+forwardGuide(function() {
   return observe(
       Discrete({ ps: [1] }),
       undefined,
       { guide: function() { return Delta({ v: 'ok' }); }});
-}}));
+});