Throw error when llvm is selected but not installed

Author: isuruf

.travis.yml

@@ -66,9 +66,23 @@ matrix:
           - g++-4.8
           - cmake
           - cmake-data
-    - env: BUILD_TYPE="Debug" WITH_BFD="yes" PYTHON_VERSION="3.5"
+    - env: BUILD_TYPE="Debug" WITH_BFD="yes" PYTHON_VERSION="3.5" WITH_LLVM="yes"
       compiler: clang
       os: linux
+      addons:
+        apt:
+          sources:
+          - ubuntu-toolchain-r-test
+          - llvm-toolchain-precise-3.8
+          - george-edison55-precise-backports
+          packages:
+          - clang
+          - libstdc++-4.8-dev
+          - libgmp-dev
+          - binutils-dev
+          - llvm-3.8-dev
+          - cmake
+          - cmake-data
     - env: BUILD_TYPE="Release" PYTHON_VERSION="2.7"
       compiler: clang
       os: linux

symengine/lib/symengine_wrapper.pyx

@@ -2831,10 +2831,13 @@ IF HAVE_SYMENGINE_LLVM:
             self.lambda_double[0].call(&out[0], &inp[0])
 
 
-def Lambdify(args, exprs, bool real=True, bool llvm=False):
-    IF HAVE_SYMENGINE_LLVM:
-        if llvm:
+def Lambdify(args, exprs, bool real=True, backend="lambda"):
+    if backend == "llvm":
+        IF HAVE_SYMENGINE_LLVM:
             return LLVMDouble(args, exprs, real)
+        ELSE:
+            raise ValueError("""llvm backend is chosen, but symengine is not compiled
+                                with llvm support.""")
 
     return LambdaDouble(args, exprs, real)
 

symengine/tests/test_lambdify.py

@@ -46,16 +46,18 @@ def allclose(vec1, vec2, rtol=1e-13, atol=1e-13):
 def test_Lambdify():
     n = 7
     args = x, y, z = se.symbols('x y z')
-    l = se.Lambdify(args, [x+y+z, x**2, (x-y)/z, x*y*z])
+    l = se.Lambdify(args, [x+y+z, x**2, (x-y)/z, x*y*z], backend='lambda')
     assert allclose(l(range(n, n+len(args))),
                     [3*n+3, n**2, -1/(n+2), n*(n+1)*(n+2)])
 
 def test_Lambdify_LLVM():
-    if not se.have_llvm:
-        return
     n = 7
     args = x, y, z = se.symbols('x y z')
-    l = se.Lambdify(args, [x+y+z, x**2, (x-y)/z, x*y*z], llvm=True)
+    if not se.have_llvm:
+        raises(ValueError, lambda: se.Lambdify(args, [x+y+z, x**2, (x-y)/z, x*y*z],
+                                                      backend='llvm'))
+        return
+    l = se.Lambdify(args, [x+y+z, x**2, (x-y)/z, x*y*z], backend='llvm')
     assert allclose(l(range(n, n+len(args))),
                     [3*n+3, n**2, -1/(n+2), n*(n+1)*(n+2)])