diff --git a/src/larktools/ebnf_grammar.py b/src/larktools/ebnf_grammar.py
index ac90bbc..a46a0ef 100644
--- a/src/larktools/ebnf_grammar.py
+++ b/src/larktools/ebnf_grammar.py
@@ -13,9 +13,8 @@
   //
   // The top level rule at which the matching/expansion process starts is named "start".
 
-  start: assign_var
+  start: multi_line_block
 
-  assign_var: VARNAME "=" multi_line_block
 
   VARNAME: LETTER (LETTER | DIGIT)*
 
@@ -25,9 +24,11 @@
   // https://lark-parser.readthedocs.io/en/stable/tree_construction.html
 
   
-  line: arith_expr
-
   multi_line_block: (line _NL? | _NL )* 
+  line: arith_expr | assignment
+
+  assignment: VARNAME "=" arith_expr
+
 
   arith_expr: sum
   sum: product | addition | subtraction 
diff --git a/src/larktools/evaluation.py b/src/larktools/evaluation.py
index c22c0d8..22b0c41 100644
--- a/src/larktools/evaluation.py
+++ b/src/larktools/evaluation.py
@@ -116,6 +116,8 @@ def eval_line(node, env):
     child_name = get_name(child)
     if child_name == "arith_expr":
         return eval_arith_expr(child, env)
+    elif child_name == "assignment":
+        return eval_assignment(child, env)
 
 def eval_multi_line_block(node, env):
     # this can be either an arithmetic expression or 
@@ -127,3 +129,15 @@ def eval_multi_line_block(node, env):
         res = eval_line(child, env)
     return res
 
+def eval_assignment(node, env):
+    # assign result of an expression to a variable
+    child1, child2 = get_children(node)[0:2]
+    assert get_name(child1) == "VARNAME"
+    assert get_name(child2) == "arith_expr"
+
+    varname = get_value(child1)
+    env[varname] = eval_arith_expr(child2, env)
+    return env[varname]
+
+
+
diff --git a/tests/test_syntax.py b/tests/test_syntax.py
index b158516..d43753d 100644
--- a/tests/test_syntax.py
+++ b/tests/test_syntax.py
@@ -18,9 +18,9 @@ def parse_and_eval(self, expression: str, env: Optional[Union[None, dict]] = Non
         return res
 
 
-def _parse_and_assert(expression: str, expected: Union[int, float]) -> None:
+def _parse_and_assert(expression: str, expected: Union[int, float], env: Optional[Union[None, dict]] = None) -> None:
     parser = SyntaxParser()
-    res = parser.parse_and_eval(expression)
+    res = parser.parse_and_eval(expression, env)
     assert expected == res
 
 def test_multi_line():
@@ -30,3 +30,24 @@ def test_multi_line():
     _parse_and_assert("5+5\n3+4\n1+2", 3)
     _parse_and_assert("\n\n5\n\n3\n8", 8)
 
+
+def test_assignment():
+    _parse_and_assert("a=5", 5)
+    _parse_and_assert("z=1+2+3", 6)
+    _parse_and_assert("y=(1+2+3)", 6)
+
+def test_assignment_env_variable():
+    # check env variables is set
+    env = {"a":1}
+    _parse_and_assert("a=3", 3, env=env)
+    assert env["a"] == 3
+
+    _parse_and_assert("y = x + 3", 20, env={"x":17, "i":123})
+    _parse_and_assert("y = x + i", 20, env={"x":17, "i":3})
+
+def test_assign_multiline():
+    _parse_and_assert("x=3 \n y=4 \n z=x+y",7)
+    _parse_and_assert("x=1 \n z = x + y", 3, env={"y":2})
+
+
+