diff --git a/Justfile b/Justfile
index b676118..49f7016 100644
--- a/Justfile
+++ b/Justfile
@@ -1,2 +1,2 @@
 watch:
-	watchexec -ce py,lark,ag -i gen 'mypy *.py && python gen.py && mypy gen/*.py'
+	watchexec -ce py,lark,ag -i gen 'mypy *.py && python agmain.py && mypy gen/*.py'
diff --git a/agast.py b/agast.py
index 19a249f..cfe79ef 100644
--- a/agast.py
+++ b/agast.py
@@ -3,28 +3,50 @@ from lark import Transformer, Tree, Token
 
 T = TypeVar("T")
 
+class Ast:
+	# def __new__(cls: Type[Ast], name: str, bases: Tuple[type], namespace: Dict[str, Any]) -> Ast:
+	# 	x = super().__new__(cls, name, bases, namespace)
+	# 	x.id = cls.__gen()
+	# 	return x
+	id: str
+	n = 0
+	@classmethod
+	def __gen(cls, name: str = "") -> str:
+		newid = cls.n
+		cls.n += 1
+		return f"_a{newid}{name}"
+	def __init__(self) -> None:
+		self.id = self.__gen()
+
 class Decl:
 	name: str
-class Iface(Decl):
-	def __init__(self, name: str):
-		self.name = name
-class IfaceField: pass
 
-class IfaceRef: pass
-class Expr: pass
+class IfaceRef(str): pass
+class IfaceField:
+	def __init__(self, name: str, ty: str):
+		self.name = name
+		self.ty = ty
+class Iface(Decl):
+	def __init__(self, name: str, fields: List[IfaceField]):
+		self.name = name
+		self.fields = fields
+
+class Expr(Ast):
+	def __init__(self) -> None:
+		super().__init__()
 
 class NodeRef: pass
-class NodeRefByName(NodeRef):
+class NodeRefByName(NodeRef, str):
 	def __init__(self, name: str):
 		self.name = name
 	def __repr__(self) -> str: return f"NodeRefByName({self.name})"
 
 class Sym: pass
 class SymRename(Sym):
-	def __init__(self, name: str, node_ref: NodeRef):
+	def __init__(self, name: str, ty: NodeRef):
 		self.name = name
-		self.node_ref = node_ref
-	def __repr__(self) -> str: return f"SymRename({self.name} : {self.node_ref})"
+		self.ty = ty
+	def __repr__(self) -> str: return f"SymRename({self.name} : {self.ty})"
 class Equation:
 	def __init__(self, lhs: Expr, rhs: Expr):
 		self.lhs = lhs
@@ -45,26 +67,31 @@ class Node(Decl):
 
 class ExprDot(Expr):
 	def __init__(self, left: Expr, right: str):
+		super().__init__()
 		self.left = left
 		self.right = right
 	def __repr__(self) -> str: return f"{self.left}.{self.right}"
 class ExprAdd(Expr):
 	def __init__(self, left: Expr, right: Expr):
+		super().__init__()
 		self.left = left
 		self.right = right
 	def __repr__(self) -> str: return f"{self.left} + {self.right}"
 class ExprMul(Expr):
 	def __init__(self, left: Expr, right: Expr):
+		super().__init__()
 		self.left = left
 		self.right = right
 	def __repr__(self) -> str: return f"{self.left} * {self.right}"
 class ExprCall(Expr):
 	def __init__(self, func: Expr, args: List[Expr]):
+		super().__init__()
 		self.func = func
 		self.args = args
 	def __repr__(self) -> str: return f"{self.func}({self.args})"
 class ExprName(Expr):
 	def __init__(self, name: str):
+		super().__init__()
 		self.name = name
 	def __repr__(self) -> str: return f"{self.name}"
 
@@ -74,10 +101,10 @@ class Parser(Transformer[List[Decl]]):
 	# interfaces
 	def iface(self, items: List[Any]) -> Iface:
 		[name, fields] = items
-		return Iface(name)
+		return Iface(name, fields)
 	def iface_field(self, items: List[str]) -> IfaceField:
 		[name, ty] = items
-		return IfaceField()
+		return IfaceField(name, ty)
 	def iface_ref(self, items: List[str]) -> str: return items[0]
 	def iface_refs(self, items: List[IfaceRef]) -> List[IfaceRef]: return items
 
@@ -98,7 +125,7 @@ class Parser(Transformer[List[Decl]]):
 
 	# equations
 	def equations(self, items: List[Equation]) -> List[Equation]: return items
-	def equation_(self, items: List[Equation]) -> Equation: return items[0]
+	def equation_semi(self, items: List[Equation]) -> Equation: return items[0]
 	def equation(self, items: List[Expr]) -> Equation: return Equation(items[0], items[1])
 
 	# expr
diff --git a/aggen.py b/aggen.py
new file mode 100644
index 0000000..d6b0b22
--- /dev/null
+++ b/aggen.py
@@ -0,0 +1,140 @@
+from typing import *
+import textwrap
+import re
+import copy
+
+from agast import *
+
+global i
+i = 0
+
+class GenResult:
+	def __init__(self, pd: str = "", ex: str = ""):
+		self.parser_data = pd
+		self.extra = ex
+
+def gen(program: List[Decl]) -> GenResult:
+	res = GenResult()
+	def gen(prefix: str = "", suffix: str = "") -> str:
+		global i
+		presan = re.sub("[^0-9a-zA-Z]+", "_", prefix)
+		sufsan = re.sub("[^0-9a-zA-Z]+", "_", suffix)
+		i += 1
+		return f"{presan}{i}{sufsan}"
+	def v(name: str) -> str:
+		return f"__ag_{name}"
+
+	# builtins
+	builtins: Dict[str, str] = {
+		"parseInt": "",
+	}
+
+	# collect a list of name -> iface declarations
+	ifaces: Dict[str, Iface] = dict(
+		map(lambda c: (c.name, cast(Iface, c)),
+		filter(lambda c: isinstance(c, Iface),
+			program)))
+	
+	# list of node -> iface mappings
+	what_ifaces: Dict[str, Set[str]] = dict()
+	what_fields: Dict[str, Dict[str, str]] = dict()
+	for node in filter(lambda c: isinstance(c, Node), program):
+		node = cast(Node, node)
+		# all_fields = dict()
+		what_ifaces[node.name] = set(node.ifaces)
+		this_fields = dict()
+		for iface in node.ifaces:
+			fields = ifaces[iface].fields
+			for field in fields:
+				if field.name in this_fields:
+					raise Exception("duplicate field name")
+				this_fields[field.name] = field.ty
+		what_fields[node.name] = this_fields
+	print("what_ifaces:", what_ifaces)
+	print("what_fields:", what_fields)
+
+	# a high-level dictionary of productions; this has sub-productions
+	# that should be further expanded at a later step before converting
+	# into lark code
+	productions_hi: Dict[str, Union[str, List[str]]] = dict()
+
+	# TODO: this should probably not be inlined here, but i'll move it
+	# out once i get more info into the 'env'
+	def collect_required_thunks(env: List[Tuple[str, NodeRef]], expr: Expr) -> Dict[str, str]:
+		names = dict(env)
+		print(f"collect_required_thunks({expr})", expr.__class__)
+		if isinstance(expr, ExprDot):
+			return collect_required_thunks(env, expr.left)
+		elif isinstance(expr, ExprMul):
+			a = collect_required_thunks(env, expr.left)
+			b = collect_required_thunks(env, expr.right)
+			a.update(b)
+			return a
+		elif isinstance(expr, ExprAdd):
+			a = collect_required_thunks(env, expr.left)
+			b = collect_required_thunks(env, expr.right)
+			a.update(b)
+			return a
+		elif isinstance(expr, ExprCall):
+			return collect_required_thunks(env, expr.func)
+		elif isinstance(expr, ExprName):
+			if expr.name not in names and expr.name not in builtins:
+				raise Exception(f"unbound name '{expr.name}'")
+			return dict()
+		raise Exception(f"unhandled {expr.__class__}")
+
+	for node in filter(lambda c: isinstance(c, Node), program):
+		node = cast(Node, node)
+		n_class_name = gen(node.name)
+		class_decl = textwrap.dedent(f"""
+			class {v(n_class_name)}: pass
+		""")
+		res.extra += class_decl
+
+		print(node.name, node.ifaces)
+
+		for variant in node.variants:
+			v_class_name = gen(f"{n_class_name}_var")
+			class_decl = textwrap.dedent(f"""
+				class {v(v_class_name)}({v(n_class_name)}):
+					''' '''
+					pass
+			""")
+			res.extra += class_decl
+
+			prod_name = gen(node.name)
+			print(prod_name)
+
+			# create an environment for checking the equations based on
+			# the production
+			env: List[Tuple[str, NodeRef]] = list()
+			for sym in variant.prod:
+				if isinstance(sym, SymRename):
+					env.append((sym.name, sym.ty))
+			print(env)
+			
+			# for each of the equations, find out what the equation is
+			# trying to compute, and generate a thunk corresponding to
+			# that value.
+			for eq in variant.equations:
+				eq_name = gen(f"eq_{node.name}")
+				thunk_name = gen(f"thunk_{node.name}")
+
+				print("RHS", eq.rhs, eq.rhs.id)
+				collect_required_thunks(copy.deepcopy(env), eq.rhs)
+
+				func_impl = textwrap.dedent(f"""
+					def {eq_name}() -> None:
+						''' {repr(eq)} '''
+						pass
+					def {thunk_name}() -> Thunk[None]:
+						return Thunk({eq_name})
+				""")
+				print(f"```py\n{func_impl}\n```")
+				res.extra += func_impl
+
+		# this is a "type alias" that connects it to one of the generated
+		# names above
+		res.extra += f"{node.name} = {v(n_class_name)}"
+
+	return res
\ No newline at end of file
diff --git a/gen.py b/agmain.py
similarity index 86%
rename from gen.py
rename to agmain.py
index abb860a..4eb5614 100644
--- a/gen.py
+++ b/agmain.py
@@ -4,7 +4,7 @@ import importlib
 from lark import Lark
 
 from agast import *
-from agtypeck import *
+from aggen import *
 
 p = Lark(open("grammar.lark").read(), start="program", parser="lalr")
 
@@ -13,22 +13,24 @@ if __name__ == "__main__":
 		data = f.read()
 
 	cst = p.parse(data)
-	# print("cst", cst)
 
 	trans = Parser()
 	ast = trans.transform(cst)
 	print("ast", ast)
 
-	res = typecheck(ast)
+	res = gen(ast)
 
 	if not os.path.exists("gen"):
 		os.makedirs("gen")
 	with open("gen/arith.py", "w") as f:
 		fmt_str = textwrap.dedent("""
 			__all__ = ["parse"]
-			from typing import Generic, TypeVar, Optional, Callable
+			from typing import Generic, TypeVar, Optional, Callable, Dict, Any
 			from lark import Lark, Transformer
 			T = TypeVar('T')
+			builtins: Dict[str, Any] = {{
+				"parseInt": lambda s: int(s)
+			}}
 			class Thunk(Generic[T]):
 				''' A thunk represents a value that may be computed lazily. '''
 				value: Optional[T]
diff --git a/agtypeck.py b/agtypeck.py
deleted file mode 100644
index 70b9e2c..0000000
--- a/agtypeck.py
+++ /dev/null
@@ -1,85 +0,0 @@
-from typing import *
-import textwrap
-import re
-from agast import *
-
-global i
-i = 0
-
-class TypecheckResult:
-	def __init__(self, pd: str = "", ex: str = ""):
-		self.parser_data = pd
-		self.extra = ex
-
-def typecheck(program: List[Decl]) -> TypecheckResult:
-	res = TypecheckResult()
-	def gen(prefix: str = "", suffix: str = "") -> str:
-		global i
-		presan = re.sub("[^0-9a-zA-Z]+", "_", prefix)
-		sufsan = re.sub("[^0-9a-zA-Z]+", "_", suffix)
-		i += 1
-		return f"{presan}{i}{sufsan}"
-	def v(name: str) -> str:
-		return f"__ag_{name}"
-
-	# collect a list of name -> iface declarations
-	ifaces: Dict[str, Decl] = dict(
-		map(lambda c: (c.name, c),
-		filter(lambda c: isinstance(c, Iface),
-			program)))
-	print(ifaces)
-
-	# a high-level dictionary of productions; this has sub-productions
-	# that should be further expanded at a later step before converting
-	# into lark code
-	productions_hi: Dict[str, Union[str, List[str]]] = dict()
-
-	for node in filter(lambda c: isinstance(c, Node), program):
-		node = cast(Node, node)
-		n_class_name = gen(node.name)
-		class_decl = textwrap.dedent(f"""
-			class {v(n_class_name)}: pass
-		""")
-		res.extra += class_decl
-
-		print(node.name, node.ifaces)
-
-		for variant in node.variants:
-			v_class_name = gen(f"{n_class_name}_var")
-			class_decl = textwrap.dedent(f"""
-				class {v(v_class_name)}({v(n_class_name)}):
-					''' '''
-					pass
-			""")
-			res.extra += class_decl
-
-			prod_name = gen(node.name)
-			print(prod_name)
-
-			for sym in variant.prod:
-				print("sym", sym)
-			
-			# for each of the equations, find out what the equation is
-			# trying to compute, and generate a thunk corresponding to
-			# that value.
-			for eq in variant.equations:
-				print("--eq", eq)
-				print(eq.lhs)
-				eq_name = gen(f"eq_{node.name}")
-				thunk_name = gen(f"thunk_{node.name}")
-
-				func_impl = textwrap.dedent(f"""
-					def {eq_name}() -> None:
-						''' {repr(eq)} '''
-						pass
-					def {thunk_name}() -> Thunk[None]:
-						return Thunk({eq_name})
-				""")
-				print(f"```py\n{func_impl}\n```")
-				res.extra += func_impl
-
-		# this is a "type alias" that connects it to one of the generated
-		# names above
-		res.extra += f"{node.name} = {v(n_class_name)}"
-
-	return res
\ No newline at end of file
diff --git a/arith.ag b/arith.ag
index 90867bc..a1008ac 100644
--- a/arith.ag
+++ b/arith.ag
@@ -4,7 +4,7 @@ iface HasValue {
 
 node Expr : HasValue {
 	<l:Expr> "+" <r:Expr> => {
-		self.val = l.val + r.val;
+		self.val = l.val + r.val * l.val;
 	}
 	<l:Expr> "*" <r:Expr> => {
 		self.val = l.val * r.val;
diff --git a/grammar.lark b/grammar.lark
index 008d538..a876b6c 100644
--- a/grammar.lark
+++ b/grammar.lark
@@ -1,8 +1,8 @@
 program: decl*
 
 ?decl: iface
-	| node
-	| func
+  | node
+  | func
 
 sep_trail{item, punc}: item (punc item)? punc?
 
@@ -17,28 +17,35 @@ node: "node" ident ":" iface_refs "{" variants "}"
 variants: variant*
 variant: prod "=>" "{" equations "}"
 prod: sym*
-sym: sym_rename
-	| STRING
+?sym: sym_rename
+  | STRING
 sym_rename: "<" ident ":" node_ref ">"
-node_ref: node_ref_name
-	| STRING
+?node_ref: node_ref_name
+  | STRING
 node_ref_name: ident
-equations: equation_*
-equation_: equation ";"
+equations: equation_semi*
+equation_semi: equation ";"
 // TODO: the left side should really be a separate type
 // called lvalue, and should NOT include literals
 equation: expr "=" expr
 
-?expr: expr_dot
-	| expr_add
-	| expr_mul
-	| expr_call
-	| expr_name
-expr_dot: expr "." expr
-expr_add: expr "+" expr
-expr_mul: expr "*" expr
-expr_call: expr "(" args ")"
+// Expressions
+?expr: expr2
+  | expr_add
+expr_add: expr "+" expr2
+
+?expr2: expr3
+  | expr_mul
+  | expr_call
+expr_mul: expr2 "*" expr3
+expr_call: expr2 "(" args ")"
+
+?expr3: "(" expr ")"
+  | expr_dot
+  | expr_name
+expr_dot: expr3 "." ident
 expr_name: ident
+
 args: sep_trail{expr, ","}
 
 ty: ident
diff --git a/main.py b/old.py
similarity index 100%
rename from main.py
rename to old.py
diff --git a/run.ps1 b/run.ps1
index 896b876..4ceda14 100644
--- a/run.ps1
+++ b/run.ps1
@@ -12,5 +12,5 @@ function Invoke-Call {
 }
 
 Invoke-Call -ScriptBlock {mypy (get-item *.py) } -ErrorAction Stop
-Invoke-Call -ScriptBlock {python gen.py } -ErrorAction Stop
+Invoke-Call -ScriptBlock {python agmain.py } -ErrorAction Stop
 Invoke-Call -ScriptBlock {mypy (get-item gen/*.py) } -ErrorAction Stop
\ No newline at end of file