diff --git a/packages/boringlang/src/parse/ast.ts b/packages/boringlang/src/parse/ast.ts
index 6fb721b..a8724ed 100644
--- a/packages/boringlang/src/parse/ast.ts
+++ b/packages/boringlang/src/parse/ast.ts
@@ -4,7 +4,7 @@ export interface Spanned {
 }
 
 export interface Identifier extends Spanned {
-  name: string;
+  text: string;
 }
 
 export interface LiteralInt {
@@ -113,11 +113,7 @@ export interface AssignmentStatement {
   expression: Expression;
 }
 
-export type Statement =
-  | ReturnStatement
-  | LetStatement
-  | AssignmentStatement
-  | Expression;
+export type Statement = ReturnStatement | LetStatement | AssignmentStatement | Expression;
 
 export interface Block {
   statements: Statement[];
@@ -141,6 +137,14 @@ export interface Function {
   block: Block;
 }
 
+export const functionToType = (fn: FunctionDeclaration): TypeUsage => {
+  return {
+    typeUsage: "FunctionTypeUsage",
+    arguments: fn.arguments.map((arg) => arg.type),
+    returnType: fn.returnType,
+  };
+};
+
 export interface StructTypeField {
   name: Identifier;
   type: TypeUsage;
diff --git a/packages/boringlang/src/parse/semantics.ts b/packages/boringlang/src/parse/semantics.ts
index e8e8598..79d4a13 100644
--- a/packages/boringlang/src/parse/semantics.ts
+++ b/packages/boringlang/src/parse/semantics.ts
@@ -50,7 +50,7 @@ semantics.addOperation<any>("toAST", {
       value: this.sourceString,
       type: {
         typeUsage: "NamedTypeUsage",
-        name: { name: "i64", spanStart: 0, spanEnd: 0 },
+        name: { text: "i64", spanStart: 0, spanEnd: 0 },
       },
     };
   },
@@ -60,7 +60,7 @@ semantics.addOperation<any>("toAST", {
       value: this.sourceString,
       type: {
         typeUsage: "NamedTypeUsage",
-        name: { name: "f64", spanStart: 0, spanEnd: 0 },
+        name: { text: "f64", spanStart: 0, spanEnd: 0 },
       },
     };
   },
@@ -70,7 +70,7 @@ semantics.addOperation<any>("toAST", {
       value: this.sourceString,
       type: {
         typeUsage: "NamedTypeUsage",
-        name: { name: "bool", spanStart: 0, spanEnd: 0 },
+        name: { text: "bool", spanStart: 0, spanEnd: 0 },
       },
     };
   },
@@ -80,7 +80,7 @@ semantics.addOperation<any>("toAST", {
       value: text.sourceString,
       type: {
         typeUsage: "NamedTypeUsage",
-        name: { name: "String", spanStart: 0, spanEnd: 0 },
+        name: { text: "String", spanStart: 0, spanEnd: 0 },
       },
     };
   },
@@ -100,7 +100,7 @@ semantics.addOperation<any>("toAST", {
   },
   identifier(_1, _2): Identifier {
     return {
-      name: this.sourceString,
+      text: this.sourceString,
       spanStart: this.source.startIdx,
       spanEnd: this.source.endIdx,
     };
@@ -197,10 +197,7 @@ semantics.addOperation<any>("toAST", {
       statementType: "LetStatement",
       variableName: ident.toAST(),
       expression: expression.toAST(),
-      type:
-        tu.length > 0
-          ? tu[0]
-          : { typeUsage: "UnknownTypeUsage", name: nextUnknown() },
+      type: tu.length > 0 ? tu[0] : { typeUsage: "UnknownTypeUsage", name: nextUnknown() },
     };
   },
   AssignmentStatement(variable, _2, expression, _4): AssignmentStatement {
@@ -248,15 +245,7 @@ semantics.addOperation<any>("toAST", {
       type: typeUsage.toAST(),
     };
   },
-  FunctionDeclaration(
-    _1,
-    identifier,
-    _3,
-    args,
-    _4,
-    _5,
-    returnType,
-  ): FunctionDeclaration {
+  FunctionDeclaration(_1, identifier, _3, args, _4, _5, returnType): FunctionDeclaration {
     return {
       name: identifier.toAST(),
       arguments: args.asIteration().children.map((c) => c.toAST()),
@@ -276,14 +265,7 @@ semantics.addOperation<any>("toAST", {
       type: typeUsage.toAST(),
     };
   },
-  StructTypeDeclaration(
-    _1,
-    identifier,
-    _3,
-    _4,
-    fields,
-    _6,
-  ): StructTypeDeclaration {
+  StructTypeDeclaration(_1, identifier, _3, _4, fields, _6): StructTypeDeclaration {
     return {
       moduleItem: "StructTypeDeclaration",
       typeDeclaration: "StructTypeDeclaration",
@@ -294,14 +276,7 @@ semantics.addOperation<any>("toAST", {
   TraitMethod(declaration, _2): FunctionDeclaration {
     return declaration.toAST();
   },
-  TraitTypeDeclaration(
-    _1,
-    identifier,
-    _3,
-    _4,
-    methods,
-    _5,
-  ): TraitTypeDeclaration {
+  TraitTypeDeclaration(_1, identifier, _3, _4, methods, _5): TraitTypeDeclaration {
     return {
       moduleItem: "TraitTypeDeclaration",
       typeDeclaration: "TraitTypeDeclaration",
diff --git a/packages/boringlang/src/types/type_checker.ts b/packages/boringlang/src/types/type_checker.ts
index e69de29..de786ee 100644
--- a/packages/boringlang/src/types/type_checker.ts
+++ b/packages/boringlang/src/types/type_checker.ts
@@ -0,0 +1,110 @@
+import { functionToType, Module, TypeUsage } from "../parse/ast";
+import { TypeSystem } from "./type_system";
+
+interface EnvImpl {
+  trait: string | null;
+  functions: Record<string, TypeUsage>;
+}
+
+interface NamedType {
+  namedEntity: "NamedType";
+  isA: "Scalar" | "Trait" | "Struct";
+  fields: Record<string, TypeUsage>;
+  impls: EnvImpl[];
+}
+
+interface Variable {
+  namedEntity: "Variable";
+  type: TypeUsage;
+}
+
+type NamedEntity = NamedType | Variable;
+
+interface Context {
+  currentFunctionReturn: TypeUsage | null;
+  environment: Record<string, NamedEntity>;
+}
+
+class TypeChecker {
+  withModule = (module: Module, typeSystem: TypeSystem) => {
+    const ctx: Context = {
+      currentFunctionReturn: null,
+      environment: {},
+    };
+    // add functions, structs, and traits to the context
+    for (const item of module.items) {
+      if (item.moduleItem === "StructTypeDeclaration") {
+        if (ctx.environment[item.name.text]) {
+          throw Error("Duplicate name of struct");
+        }
+        ctx.environment[item.name.text] = {
+          namedEntity: "NamedType",
+          isA: "Struct",
+          fields: Object.fromEntries(item.fields.map((field) => [field.name, field.type])),
+          impls: [],
+        };
+      }
+      if (item.moduleItem === "TraitTypeDeclaration") {
+        if (ctx.environment[item.name.text]) {
+          throw Error("Duplicate name of trait");
+        }
+        ctx.environment[item.name.text] = {
+          namedEntity: "NamedType",
+          isA: "Trait",
+          fields: {},
+          impls: [
+            {
+              trait: item.name.text,
+              functions: Object.fromEntries(
+                item.functions.map((fn) => {
+                  return [fn.name, functionToType(fn)];
+                }),
+              ),
+            },
+          ],
+        };
+      }
+      if (item.moduleItem === "Function") {
+        if (ctx.environment[item.declaration.name.text]) {
+          throw Error("Duplicate name of function");
+        }
+        ctx.environment[item.declaration.name.text] = {
+          namedEntity: "Variable",
+          type: functionToType(item.declaration),
+        };
+      }
+    }
+    // now that structs and traits are added, add impls
+    for (const item of module.items) {
+      if (item.moduleItem === "Impl") {
+        const struct = ctx.environment[item.struct.name.text];
+        if (!struct || struct.namedEntity !== "NamedType" || struct.isA !== "Struct") {
+          throw Error("Impl for non-struct");
+        }
+        struct.impls.push({
+          trait: item.trait?.name.text ?? null,
+          functions: Object.fromEntries(
+            item.functions.map((fn) => {
+              return [fn.declaration.name, functionToType(fn.declaration)];
+            }),
+          ),
+        });
+      }
+    }
+    // environment set up, actually recurse.
+    for (const item of module.items) {
+      if (item.moduleItem === "Function") {
+        // this.withFunction(item, typeSystem);
+      }
+      if (item.moduleItem === "Impl") {
+        // this.withImpl(item, typeSystem);
+      }
+      if (item.moduleItem === "StructTypeDeclaration") {
+        // this.withImpl(item, typeSystem);
+      }
+      if (item.moduleItem === "TraitTypeDeclaration") {
+        // this.withTrait(item, typeSystem);
+      }
+    }
+  };
+}
diff --git a/packages/boringlang/src/types/type_system.ts b/packages/boringlang/src/types/type_system.ts
index 8c160c8..cdf01af 100644
--- a/packages/boringlang/src/types/type_system.ts
+++ b/packages/boringlang/src/types/type_system.ts
@@ -5,8 +5,8 @@ export const compareTypes = (typeA: TypeUsage, typeB: TypeUsage) => {
     throw Error(`Mismatched types: ${typeA.typeUsage} ${typeB.typeUsage}`);
   }
   if (typeA.typeUsage == "NamedTypeUsage" && typeB.typeUsage == "NamedTypeUsage") {
-    if (typeA.name.name !== typeB.name.name) {
-      throw Error(`Mismatched types: ${typeA.name.name} ${typeB.name.name}`);
+    if (typeA.name.text !== typeB.name.text) {
+      throw Error(`Mismatched types: ${typeA.name.text} ${typeB.name.text}`);
     }
   }
   if (typeA.typeUsage == "FunctionTypeUsage" && typeB.typeUsage == "FunctionTypeUsage") {
@@ -39,7 +39,7 @@ interface Comparison {
   right: TypeUsage;
 }
 
-class TypeSystem {
+export class TypeSystem {
   comparisons: Comparison[];
   result: Record<string, TypeUsage>;