Adds a check if the prior is set when using marg. likel.

If the prior is not given to the likelihood when using the marginalized
likelihood, marginalization cannot be safely performed. This adds a
check and raises a ValueError if it is not set.

Closes #88

tupak/gw/likelihood.py

@@ -64,6 +64,7 @@ class GravitationalWaveTransient(likelihood.Likelihood):
         self.prior = prior
 
         if self.distance_marginalization:
+            self.check_prior_is_set()
             self.distance_array = np.array([])
             self.delta_distance = 0
             self.distance_prior_array = np.array([])
@@ -71,10 +72,18 @@ class GravitationalWaveTransient(likelihood.Likelihood):
             prior['luminosity_distance'] = 1  # this means the prior is a delta function fixed at the RHS value
 
         if self.phase_marginalization:
+            self.check_prior_is_set()
             self.bessel_function_interped = None
             self.setup_phase_marginalization()
             prior['phase'] = 0
 
+        if self.time_marginalization:
+            self.check_prior_is_set()
+
+    def check_prior_is_set(self):
+        if self.prior is None:
+            raise ValueError("You can't use a marginalized likelihood without specifying a prior")
+
     @property
     def prior(self):
         return self.__prior