diff --git a/examples/strings.bl b/examples/strings.bl
index 0397bda..56e9f8f 100644
--- a/examples/strings.bl
+++ b/examples/strings.bl
@@ -1,6 +1,6 @@
-fn main(): String {
-  let a = "asdf";
-  return a ;
+fn main(): i64 {
+  let user = User{id: 4};
+  return user.instance_method();
 }
 
 type User struct {
diff --git a/packages/boringlang/src/commands/run.ts b/packages/boringlang/src/commands/run.ts
index c0fce2e..cd3b4fc 100644
--- a/packages/boringlang/src/commands/run.ts
+++ b/packages/boringlang/src/commands/run.ts
@@ -6,6 +6,7 @@ import { TypeAliasResolver } from "../types/type_alias_resolution";
 import { TypeSystem } from "../types/type_system";
 import { TypeChecker } from "../types/type_checker";
 import { TypeResolver } from "../types/type_resolver";
+import { TreeWalkInterpreter } from "../interpreter";
 
 export const run = defineCommand({
   name: "run",
@@ -33,7 +34,9 @@ export const run = defineCommand({
       typeChecker.withModule(aliasResolvedAst, typeSystem);
       typeSystem.solve();
       const typeResolvedAst = typeResolver.withModule(aliasResolvedAst, typeSystem);
-      console.log(JSON.stringify(typeResolvedAst, null, 2));
+      const interpreter = new TreeWalkInterpreter();
+      const result = interpreter.withModule(typeResolvedAst);
+      console.log(JSON.stringify(result, null, 2));
 
       // console.log(JSON.stringify(aliasResolvedAst, null, 2));
     } else {
diff --git a/packages/boringlang/src/interpreter/builtins.ts b/packages/boringlang/src/interpreter/builtins.ts
new file mode 100644
index 0000000..75091fe
--- /dev/null
+++ b/packages/boringlang/src/interpreter/builtins.ts
@@ -0,0 +1,92 @@
+import { Module } from "../parse/ast";
+import { Context, FunctionRef } from "./context";
+
+export function contextFromModule(module: Module): Context {
+  const ctx: Context = {
+    environment: {},
+    currentModule: module,
+  };
+  ctx.environment["i8"] = { namedEntity: "NamedType", isA: "Scalar", fields: {}, impls: [] };
+  ctx.environment["i16"] = { namedEntity: "NamedType", isA: "Scalar", fields: {}, impls: [] };
+  ctx.environment["i32"] = { namedEntity: "NamedType", isA: "Scalar", fields: {}, impls: [] };
+  ctx.environment["i64"] = { namedEntity: "NamedType", isA: "Scalar", fields: {}, impls: [] };
+  ctx.environment["f8"] = { namedEntity: "NamedType", isA: "Scalar", fields: {}, impls: [] };
+  ctx.environment["f16"] = { namedEntity: "NamedType", isA: "Scalar", fields: {}, impls: [] };
+  ctx.environment["f32"] = { namedEntity: "NamedType", isA: "Scalar", fields: {}, impls: [] };
+  ctx.environment["f64"] = { namedEntity: "NamedType", isA: "Scalar", fields: {}, impls: [] };
+  ctx.environment["String"] = { namedEntity: "NamedType", isA: "Scalar", fields: {}, impls: [] };
+  ctx.environment["Void"] = { namedEntity: "NamedType", isA: "Scalar", fields: {}, impls: [] };
+  ctx.environment["Never"] = { namedEntity: "NamedType", isA: "Scalar", fields: {}, impls: [] };
+
+  // add functions, structs, and traits to the context
+  for (const item of module.items) {
+    if (item.moduleItem === "StructTypeDeclaration") {
+      ctx.environment[item.name.text] = {
+        namedEntity: "NamedType",
+        isA: "Struct",
+        fields: Object.fromEntries(item.fields.map((field) => [field.name.text, field.type])),
+        impls: [],
+      };
+    }
+    if (item.moduleItem === "TraitTypeDeclaration") {
+      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,
+                  {
+                    functionType: "UserFunction",
+                    function: fn,
+                  },
+                ];
+              }),
+            ),
+          },
+        ],
+      };
+    }
+    if (item.moduleItem === "Function") {
+      ctx.environment[item.declaration.name.text] = {
+        namedEntity: "Variable",
+        value: {
+          value: "FunctionValue",
+          partial: [],
+          ref: {
+            functionType: "UserFunction",
+            function: item,
+          },
+        },
+      };
+    }
+  }
+  // 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");
+      }
+      const functions: Record<string, FunctionRef> = {};
+      for (const fn of item.functions) {
+        if (
+          fn.declaration.arguments.length &&
+          fn.declaration.arguments[0].type.typeUsage == "NamedTypeUsage" &&
+          fn.declaration.arguments[0].type.name.text === item.struct.name.text
+        ) {
+          functions[fn.declaration.name.text] = { functionType: "UserFunction", function: fn };
+        }
+      }
+      struct.impls.push({
+        trait: item.trait?.name.text ?? null,
+        functions: functions,
+      });
+    }
+  }
+  return ctx;
+}
diff --git a/packages/boringlang/src/interpreter/context.ts b/packages/boringlang/src/interpreter/context.ts
new file mode 100644
index 0000000..5a48292
--- /dev/null
+++ b/packages/boringlang/src/interpreter/context.ts
@@ -0,0 +1,74 @@
+import { TypeUsage, Function, Module } from "../parse/ast";
+
+export interface NumericValue {
+  value: "NumericValue";
+  number: number;
+}
+
+export interface BoolValue {
+  value: "BoolValue";
+  bool: boolean;
+}
+
+export interface StringValue {
+  value: "StringValue";
+  string: string;
+}
+
+export interface UserFunction {
+  functionType: "UserFunction";
+  function: Function;
+}
+
+export interface BuiltinFunction {
+  functionType: "BuiltinFunction";
+  function: (value: Value[]) => Value;
+}
+
+export type FunctionRef = UserFunction | BuiltinFunction;
+
+export interface FunctionValue {
+  value: "FunctionValue";
+  partial: Value[];
+  ref: FunctionRef;
+}
+
+export interface UnitValue {
+  value: "UnitValue";
+}
+
+export interface StructValue {
+  value: "StructValue";
+  source: NamedType;
+  fields: Record<string, Value>;
+}
+
+export type Value =
+  | NumericValue
+  | BoolValue
+  | StringValue
+  | FunctionValue
+  | StructValue
+  | UnitValue;
+
+export interface Variable {
+  namedEntity: "Variable";
+  value: Value;
+}
+
+export interface EnvImpl {
+  trait: string | null;
+  functions: Record<string, FunctionRef>;
+}
+
+export interface NamedType {
+  namedEntity: "NamedType";
+  isA: "Scalar" | "Trait" | "Struct";
+  fields: Record<string, TypeUsage>;
+  impls: EnvImpl[];
+}
+
+export interface Context {
+  environment: Record<string, NamedType | Variable>;
+  currentModule: Module;
+}
diff --git a/packages/boringlang/src/interpreter/index.ts b/packages/boringlang/src/interpreter/index.ts
new file mode 100644
index 0000000..4d06b57
--- /dev/null
+++ b/packages/boringlang/src/interpreter/index.ts
@@ -0,0 +1,305 @@
+import {
+  AssignmentStatement,
+  Block,
+  Expression,
+  Function,
+  FunctionCall,
+  LetStatement,
+  Module,
+  Operation,
+  ReturnStatement,
+  StructGetter,
+  StructTypeDeclaration,
+  TypeUsage,
+} from "../parse/ast";
+import { contextFromModule } from "./builtins";
+import { Context, Value } from "./context";
+
+interface ExpressionResultValue {
+  resultType: "Value";
+  value: Value;
+}
+
+interface ExpressionResultReturn {
+  resultType: "Return";
+  value: Value;
+}
+
+type ExpressionResult = ExpressionResultValue | ExpressionResultReturn;
+
+export class TreeWalkInterpreter {
+  withModule = (module: Module) => {
+    const ctx = contextFromModule(module);
+    const main = ctx.environment["main"];
+    if (
+      !main ||
+      !(main.namedEntity === "Variable") ||
+      !(main.value.value === "FunctionValue") ||
+      !(main.value.ref.functionType === "UserFunction")
+    ) {
+      throw Error("No main function");
+    }
+    return this.withFunction(ctx, main.value.ref.function);
+  };
+
+  withFunction = (ctx: Context, fn: Function): Value => {
+    let result = this.withBlock(ctx, fn.block);
+    return result.value;
+  };
+
+  withBlock = (ctx: Context, block: Block): ExpressionResult => {
+    let last: ExpressionResult = { resultType: "Value", value: { value: "UnitValue" } };
+    for (const statement of block.statements) {
+      if (statement.statementType === "AssignmentStatement") {
+        last = this.withAssignmentStatement(ctx, statement);
+      }
+      if (statement.statementType === "LetStatement") {
+        last = this.withLetStatement(ctx, statement);
+      }
+      if (statement.statementType === "Expression") {
+        last = this.withExpression(ctx, statement);
+      }
+      if (statement.statementType === "ReturnStatement") {
+        last = this.withReturnStatement(ctx, statement);
+      }
+      if (last.resultType === "Return") {
+        return last;
+      }
+    }
+    return last;
+  };
+
+  withAssignmentStatement = (ctx: Context, statement: AssignmentStatement): ExpressionResult => {
+    let result = this.withExpression(ctx, statement.expression);
+    if (result.resultType === "Return") {
+      return result;
+    }
+    if (statement.source.expressionType == "VariableUsage") {
+      ctx.environment[statement.source.name.text] = {
+        namedEntity: "Variable",
+        value: result.value,
+      };
+    }
+    if (statement.source.expressionType == "StructGetter") {
+      let source = this.withStructGetter(ctx, statement.source);
+      if (source.resultType === "Return") {
+        return source;
+      }
+      if (source.value.value !== "StructValue") {
+        throw Error("set attr on nonstruct, should never happen due to type system");
+      }
+      source.value.fields[statement.source.attribute.text] = result.value;
+    }
+    return { resultType: "Value", value: { value: "UnitValue" } };
+  };
+
+  withLetStatement = (ctx: Context, statement: LetStatement): ExpressionResult => {
+    let result = this.withExpression(ctx, statement.expression);
+    if (result.resultType === "Return") {
+      return result;
+    }
+    ctx.environment[statement.variableName.text] = {
+      namedEntity: "Variable",
+      value: result.value,
+    };
+    return { resultType: "Value", value: { value: "UnitValue" } };
+  };
+
+  withReturnStatement = (ctx: Context, statement: ReturnStatement): ExpressionResult => {
+    let result = this.withExpression(ctx, statement.source);
+    if (result.resultType === "Return") {
+      return result;
+    }
+    return { resultType: "Return", value: result.value };
+  };
+
+  withExpression = (ctx: Context, expression: Expression): ExpressionResult => {
+    if (expression.subExpression.expressionType === "LiteralInt") {
+      return {
+        resultType: "Value",
+        value: { value: "NumericValue", number: parseInt(expression.subExpression.value) },
+      };
+    }
+    if (expression.subExpression.expressionType === "LiteralFloat") {
+      return {
+        resultType: "Value",
+        value: { value: "NumericValue", number: parseFloat(expression.subExpression.value) },
+      };
+    }
+    if (expression.subExpression.expressionType === "LiteralString") {
+      return {
+        resultType: "Value",
+        value: { value: "StringValue", string: expression.subExpression.value },
+      };
+    }
+    if (expression.subExpression.expressionType === "LiteralBool") {
+      return {
+        resultType: "Value",
+        value: { value: "BoolValue", bool: expression.subExpression.value === "true" },
+      };
+    }
+    if (expression.subExpression.expressionType === "LiteralStruct") {
+      const def = ctx.environment[expression.subExpression.name.text];
+      if (def.namedEntity !== "NamedType") {
+        throw Error("Not a struct");
+      }
+      const fields: Record<string, Value> = {};
+      for (const field of expression.subExpression.fields) {
+        const fieldResult = this.withExpression(ctx, field.expression);
+        if (fieldResult.resultType === "Return") {
+          return fieldResult;
+        }
+        fields[field.name.text] = fieldResult.value;
+      }
+      return {
+        resultType: "Value",
+        value: {
+          value: "StructValue",
+          source: def,
+          fields: fields,
+        },
+      };
+    }
+    if (expression.subExpression.expressionType === "FunctionCall") {
+      return this.withFunctionCall(ctx, expression.subExpression);
+    }
+    if (expression.subExpression.expressionType === "VariableUsage") {
+      const variableValue = ctx.environment[expression.subExpression.name.text];
+      if (!variableValue || variableValue.namedEntity !== "Variable") {
+        throw Error(`not found: ${expression.subExpression.name.text}`);
+      }
+      return { resultType: "Value", value: variableValue.value };
+    }
+    if (expression.subExpression.expressionType === "IfExpression") {
+      const condition = this.withExpression(ctx, expression.subExpression.condition);
+      if (condition.resultType === "Return") {
+        return condition;
+      }
+      if (condition.value.value === "BoolValue" && condition.value.bool === true) {
+        return this.withBlock(ctx, expression.subExpression.block);
+      } else {
+        if (expression.subExpression.else) {
+          return this.withBlock(ctx, expression.subExpression.else);
+        } else {
+          return { resultType: "Value", value: { value: "UnitValue" } };
+        }
+      }
+    }
+    if (expression.subExpression.expressionType === "StructGetter") {
+      return this.withStructGetter(ctx, expression.subExpression);
+    }
+    if (expression.subExpression.expressionType === "Block") {
+      return this.withBlock(ctx, expression.subExpression);
+    }
+    if (expression.subExpression.expressionType === "Operation") {
+      return this.withOperation(ctx, expression.subExpression);
+    }
+    // not actually possible, but makes the type system happy
+    return { resultType: "Value", value: { value: "UnitValue" } };
+  };
+
+  withFunctionCall = (ctx: Context, fnCall: FunctionCall): ExpressionResult => {
+    const source = this.withExpression(ctx, fnCall.source);
+    if (source.resultType === "Return") {
+      return source;
+    }
+    const argValues: Value[] = [];
+    for (const arg of fnCall.arguments) {
+      const argValue = this.withExpression(ctx, arg);
+      if (argValue.resultType === "Return") {
+        return argValue;
+      }
+      argValues.push(argValue.value);
+    }
+    if (source.value.value !== "FunctionValue") {
+      throw Error("type error: function call source must be a function");
+    }
+    if (source.value.ref.functionType === "UserFunction") {
+      const fn = source.value.partial;
+      const fnCtx = contextFromModule(ctx.currentModule);
+      let i = 0;
+      for (const arg of source.value.partial) {
+        fnCtx.environment[source.value.ref.function.declaration.arguments[i].name.text] = {
+          namedEntity: "Variable",
+          value: arg,
+        };
+        i = i + 1;
+      }
+      for (const arg of argValues) {
+        fnCtx.environment[source.value.ref.function.declaration.arguments[i].name.text] = {
+          namedEntity: "Variable",
+          value: arg,
+        };
+        i = i + 1;
+      }
+      return { resultType: "Value", value: this.withFunction(fnCtx, source.value.ref.function) };
+    }
+    // builtin
+    let allValues = source.value.partial.concat(argValues);
+    return { resultType: "Value", value: source.value.ref.function(allValues) };
+  };
+
+  withStructGetter = (ctx: Context, structGetter: StructGetter): ExpressionResult => {
+    const source = this.withExpression(ctx, structGetter.source);
+    if (source.resultType === "Return") {
+      return source;
+    }
+    if (source.value.value !== "StructValue") {
+      throw Error("get attr of non-struct");
+    }
+    if (source.value.fields[structGetter.attribute.text]) {
+      return {
+        resultType: "Value",
+        value: source.value.fields[structGetter.attribute.text],
+      };
+    }
+    for (const impl of source.value.source.impls) {
+      for (const [name, method] of Object.entries(impl.functions)) {
+        if (name === structGetter.attribute.text) {
+          return {
+            resultType: "Value",
+            value: { value: "FunctionValue", partial: [source.value], ref: method },
+          };
+        }
+      }
+    }
+    // not actually possible, but makes the type system happy
+    return { resultType: "Value", value: { value: "UnitValue" } };
+  };
+
+  withOperation = (ctx: Context, op: Operation): ExpressionResult => {
+    const left = this.withExpression(ctx, op.left);
+    if (left.resultType === "Return") {
+      return left;
+    }
+    const right = this.withExpression(ctx, op.left);
+    if (right.resultType === "Return") {
+      return right;
+    }
+    if (left.value.value !== "NumericValue" || right.value.value !== "NumericValue") {
+      throw Error("Operation on a Nan");
+    }
+    if (op.op === "+") {
+      return {
+        resultType: "Value",
+        value: { value: "NumericValue", number: left.value.number + right.value.number },
+      };
+    }
+    if (op.op === "-") {
+      return {
+        resultType: "Value",
+        value: { value: "NumericValue", number: left.value.number - right.value.number },
+      };
+    }
+    if (op.op === "*") {
+      return {
+        resultType: "Value",
+        value: { value: "NumericValue", number: left.value.number * right.value.number },
+      };
+    }
+    return {
+      resultType: "Value",
+      value: { value: "NumericValue", number: left.value.number / right.value.number },
+    };
+  };
+}