diff --git a/src/Push.hs b/src/Push.hs
index d5554bb..495782a 100644
--- a/src/Push.hs
+++ b/src/Push.hs
@@ -41,20 +41,28 @@ emptyState =
 -- Everntually, this can be part of the apply func to state helpers,
 -- which should take the number and type of parameter they have.
 instructionIntAdd :: State -> State
-instructionIntAdd (State es [] fs bs ss ps) = State es [] fs bs ss ps
 instructionIntAdd (State es (i : is) fs bs ss ps) = State es ((head is + i) : drop 1 is) fs bs ss ps
+instructionIntAdd state = state
 
-instructionIntSubtract :: State -> State
-instructionIntSubtract (State es [] fs bs ss ps) = State es [] fs bs ss ps
-instructionIntSubtract (State es (i : is) fs bs ss ps) = State es ((head is - i) : drop 1 is) fs bs ss ps
+instructionIntSub :: State -> State
+instructionIntSub (State es (i : is) fs bs ss ps) = State es ((head is - i) : drop 1 is) fs bs ss ps
+instructionIntSub state = state
 
-instructionIntMultiply :: State -> State
-instructionIntMultiply (State es [] fs bs ss ps) = State es [] fs bs ss ps
-instructionIntMultiply (State es (i : is) fs bs ss ps) = State es ((head is * i) : drop 1 is) fs bs ss ps
+instructionIntMul :: State -> State
+instructionIntMul (State es (i : is) fs bs ss ps) = State es ((head is * i) : drop 1 is) fs bs ss ps
+instructionIntMul state = state
 
-instructionIntDivide :: State -> State
-instructionIntDivide (State es [] fs bs ss ps) = State es [] fs bs ss ps
-instructionIntDivide (State es (i : is) fs bs ss ps) = State es (div (head is) i : drop 1 is) fs bs ss ps
+instructionIntDiv :: State -> State
+instructionIntDiv (State es (i : is) fs bs ss ps) = State es (div (head is) i : drop 1 is) fs bs ss ps
+instructionIntDiv state = state
+
+instructionExecIf :: State -> State
+instructionExecIf (State es is fs [] ss ps) = (State es is fs [] ss ps)
+instructionExecIf (State (e : es) is fs bs ss ps) =
+  case head bs of
+    True -> State (e : drop 1 es) is fs bs ss ps
+    False -> State (es) is fs bs ss ps
+instructionExecIf state = state
 
 -- This is one of the push genome functions itself, not infrastructure.
 -- Optionally, split this off into independent functions
@@ -98,7 +106,7 @@ interpretExec (State (e : es) is fs bs ss ps) =
     (BoolGene val) -> interpretExec (State es is fs (val : bs) ss ps)
     (StringGene val) -> interpretExec (State es is fs bs (val : ss) ps)
     (StateFunc func) -> interpretExec (func (State es is fs bs ss ps))
-    (Block block) -> interpretExec (State (reverse block ++ es) is fs bs ss ps)
+    (Block block) -> interpretExec (State (block ++ es) is fs bs ss ps)
 
 -- The safety of interpretExec on empty stacks depends on the functions it calls.
 -- Need to make interpretExec strict, right?
diff --git a/src/Tests.hs b/src/Tests.hs
index 05fc6a3..2966ff9 100644
--- a/src/Tests.hs
+++ b/src/Tests.hs
@@ -14,16 +14,21 @@ exampleState =
 
 testResult1 = [8, 3] == int (instructionIntAdd exampleState)
 
-testResult2 = [4, 3] == int (instructionIntSubtract exampleState)
+testResult2 = [4, 3] == int (instructionIntSub exampleState)
 
-testResult3 = [12, 3] == int (instructionIntMultiply exampleState)
+testResult3 = [12, 3] == int (instructionIntMul exampleState)
 
-testResult4 = [3, 3] == int (instructionIntDivide exampleState)
+testResult4 = [3, 3] == int (instructionIntDiv exampleState)
 
 testResult5 = [6, 2, 6, 3] == int (interpretExec exampleState)
 
 loadedState = loadProgarm [IntGene 6, IntGene 6, StateFunc instructionIntAdd] emptyState
-
 testResult6 = [12] == int (interpretExec loadedState)
 
-allTests = and [testResult1, testResult2, testResult3, testResult4, testResult5, testResult6]
+loadedState2 = loadProgarm [BoolGene True, StateFunc instructionExecIf, Block [IntGene 5, IntGene 6], Block [IntGene 7, IntGene 8]] emptyState
+testResult7 = [6, 5] == int (interpretExec loadedState2)
+
+loadedState3 = loadProgarm [BoolGene False, StateFunc instructionExecIf, Block [IntGene 5, IntGene 6], Block [IntGene 7, IntGene 8]] emptyState
+testResult8 = [8, 7] == int (interpretExec loadedState3)
+
+allTests = and [testResult1, testResult2, testResult3, testResult4, testResult5, testResult6, testResult7, testResult8]
\ No newline at end of file