Only call precompile during package precompilation

src/Persefone.jl

@@ -149,8 +149,12 @@ include("nature/species/wyvern.jl")
 
 include("core/simulation.jl") #this must be last
 
-# precompile important functions - TODO use PrecompileTools.jl
-precompile(initialise, (String,Int))
-precompile(stepsimulation!, (SimulationModel,))
-
+function _precompile()
+    precompile(initialise, (String,Int))
+    precompile(stepsimulation!, (SimulationModel,))
+end
+if ccall(:jl_generating_output, Cint, ()) == 1
+    # only run this during precompilation
+    _precompile()
+end
 end