feat: IS_PRIMOP

nix-js/build.rs

@@ -1,6 +1,6 @@
-use std::process::Command;
-use std::path::Path;
 use std::env;
+use std::path::Path;
+use std::process::Command;
 
 fn main() {
     let runtime_ts_dir = Path::new("runtime-ts");
@@ -17,7 +17,11 @@ fn main() {
 
     if !runtime_ts_dir.join("node_modules").exists() {
         println!("Installing npm dependencies...");
-        let npm_cmd = if cfg!(target_os = "windows") { "npm.cmd" } else { "npm" };
+        let npm_cmd = if cfg!(target_os = "windows") {
+            "npm.cmd"
+        } else {
+            "npm"
+        };
         let status = Command::new(npm_cmd)
             .arg("install")
             .current_dir(runtime_ts_dir)
@@ -30,7 +34,11 @@ fn main() {
     }
 
     println!("Running TypeScript type checking...");
-    let npm_cmd = if cfg!(target_os = "windows") { "npm.cmd" } else { "npm" };
+    let npm_cmd = if cfg!(target_os = "windows") {
+        "npm.cmd"
+    } else {
+        "npm"
+    };
     let status = Command::new(npm_cmd)
         .arg("run")
         .arg("typecheck")

nix-js/runtime-ts/src/builtins/index.ts

@@ -5,6 +5,98 @@
 
 import { create_thunk } from '../thunk';
 
+/**
+ * Symbol used to mark functions as primops (primitive operations)
+ * This is similar to IS_THUNK but for builtin functions
+ */
+export const IS_PRIMOP = Symbol('is_primop');
+
+/**
+ * Metadata interface for primop functions
+ */
+export interface PrimopMetadata {
+  /** The name of the primop (e.g., "add", "map") */
+  name: string;
+  /** Total arity of the function (number of arguments it expects) */
+  arity: number;
+  /** Number of arguments already applied (for partial applications) */
+  applied: number;
+}
+
+/**
+ * Mark a function as a primop with metadata
+ * For curried functions, this recursively marks each layer
+ *
+ * @param func - The function to mark
+ * @param name - Name of the primop
+ * @param arity - Total number of arguments expected
+ * @param applied - Number of arguments already applied (default: 0)
+ * @returns The marked function
+ */
+export const markPrimop = <T extends Function>(
+  func: T,
+  name: string,
+  arity: number,
+  applied: number = 0
+): T => {
+  // Mark this function as a primop
+  (func as any)[IS_PRIMOP] = {
+    name,
+    arity,
+    applied,
+  } as PrimopMetadata;
+
+  // If this is a curried function and not fully applied,
+  // wrap it to mark the next layer too
+  if (applied < arity - 1) {
+    const wrappedFunc = ((...args: any[]) => {
+      const result = func(...args);
+      // If result is a function, mark it as the next layer
+      if (typeof result === 'function') {
+        return markPrimop(result, name, arity, applied + args.length);
+      }
+      return result;
+    }) as any;
+
+    // Copy the primop metadata to the wrapper
+    wrappedFunc[IS_PRIMOP] = {
+      name,
+      arity,
+      applied,
+    } as PrimopMetadata;
+
+    return wrappedFunc as T;
+  }
+
+  return func;
+};
+
+/**
+ * Type guard to check if a value is a primop
+ * @param value - Value to check
+ * @returns true if value is marked as a primop
+ */
+export const is_primop = (value: unknown): value is Function & { [IS_PRIMOP]: PrimopMetadata } => {
+  return (
+    typeof value === 'function' &&
+    IS_PRIMOP in value &&
+    typeof value[IS_PRIMOP] === 'object' &&
+    value[IS_PRIMOP] !== null
+  );
+};
+
+/**
+ * Get primop metadata from a function
+ * @param func - Function to get metadata from
+ * @returns Metadata if function is a primop, undefined otherwise
+ */
+export const get_primop_metadata = (func: unknown): PrimopMetadata | undefined => {
+  if (is_primop(func)) {
+    return func[IS_PRIMOP];
+  }
+  return undefined;
+};
+
 // Import all builtin categories
 import * as arithmetic from './arithmetic';
 import * as math from './math';
@@ -24,144 +116,133 @@ import * as misc from './misc';
  * All functions are curried for Nix semantics:
  * - Single argument functions: (a) => result
  * - Multi-argument functions: (a) => (b) => result
+ *
+ * All primop functions are marked with IS_PRIMOP symbol for runtime introspection
  */
 export const builtins: any = {
-  // Arithmetic (curried binary functions)
-  add: arithmetic.add,
-  sub: arithmetic.sub,
-  mul: arithmetic.mul,
-  div: arithmetic.div,
-  bitAnd: arithmetic.bitAnd,
-  bitOr: arithmetic.bitOr,
-  bitXor: arithmetic.bitXor,
-  lessThan: arithmetic.lessThan,
+  add: markPrimop(arithmetic.add, 'add', 2),
+  sub: markPrimop(arithmetic.sub, 'sub', 2),
+  mul: markPrimop(arithmetic.mul, 'mul', 2),
+  div: markPrimop(arithmetic.div, 'div', 2),
+  bitAnd: markPrimop(arithmetic.bitAnd, 'bitAnd', 2),
+  bitOr: markPrimop(arithmetic.bitOr, 'bitOr', 2),
+  bitXor: markPrimop(arithmetic.bitXor, 'bitXor', 2),
+  lessThan: markPrimop(arithmetic.lessThan, 'lessThan', 2),
 
-  // Math
-  ceil: math.ceil,
-  floor: math.floor,
+  ceil: markPrimop(math.ceil, 'ceil', 1),
+  floor: markPrimop(math.floor, 'floor', 1),
 
-  // Type checking
-  isAttrs: typeCheck.isAttrs,
-  isBool: typeCheck.isBool,
-  isFloat: typeCheck.isFloat,
-  isFunction: typeCheck.isFunction,
-  isInt: typeCheck.isInt,
-  isList: typeCheck.isList,
-  isNull: typeCheck.isNull,
-  isPath: typeCheck.isPath,
-  isString: typeCheck.isString,
-  typeOf: typeCheck.typeOf,
+  isAttrs: markPrimop(typeCheck.isAttrs, 'isAttrs', 1),
+  isBool: markPrimop(typeCheck.isBool, 'isBool', 1),
+  isFloat: markPrimop(typeCheck.isFloat, 'isFloat', 1),
+  isFunction: markPrimop(typeCheck.isFunction, 'isFunction', 1),
+  isInt: markPrimop(typeCheck.isInt, 'isInt', 1),
+  isList: markPrimop(typeCheck.isList, 'isList', 1),
+  isNull: markPrimop(typeCheck.isNull, 'isNull', 1),
+  isPath: markPrimop(typeCheck.isPath, 'isPath', 1),
+  isString: markPrimop(typeCheck.isString, 'isString', 1),
+  typeOf: markPrimop(typeCheck.typeOf, 'typeOf', 1),
 
-  // List operations
-  map: list.map,
-  filter: list.filter,
-  length: list.length,
-  head: list.head,
-  tail: list.tail,
-  elem: list.elem,
-  elemAt: list.elemAt,
-  concatLists: list.concatLists,
-  concatMap: list.concatMap,
-  'foldl\'': list.foldlPrime,
-  sort: list.sort,
-  partition: list.partition,
-  genList: list.genList,
-  all: list.all,
-  any: list.any,
+  map: markPrimop(list.map, 'map', 2),
+  filter: markPrimop(list.filter, 'filter', 2),
+  length: markPrimop(list.length, 'length', 1),
+  head: markPrimop(list.head, 'head', 1),
+  tail: markPrimop(list.tail, 'tail', 1),
+  elem: markPrimop(list.elem, 'elem', 2),
+  elemAt: markPrimop(list.elemAt, 'elemAt', 2),
+  concatLists: markPrimop(list.concatLists, 'concatLists', 1),
+  concatMap: markPrimop(list.concatMap, 'concatMap', 2),
+  'foldl\'': markPrimop(list.foldlPrime, 'foldl\'', 3),
+  sort: markPrimop(list.sort, 'sort', 2),
+  partition: markPrimop(list.partition, 'partition', 2),
+  genList: markPrimop(list.genList, 'genList', 2),
+  all: markPrimop(list.all, 'all', 2),
+  any: markPrimop(list.any, 'any', 2),
 
-  // Attribute set operations
-  attrNames: attrs.attrNames,
-  attrValues: attrs.attrValues,
-  getAttr: attrs.getAttr,
-  hasAttr: attrs.hasAttr,
-  mapAttrs: attrs.mapAttrs,
-  listToAttrs: attrs.listToAttrs,
-  intersectAttrs: attrs.intersectAttrs,
-  catAttrs: attrs.catAttrs,
-  groupBy: attrs.groupBy,
+  attrNames: markPrimop(attrs.attrNames, 'attrNames', 1),
+  attrValues: markPrimop(attrs.attrValues, 'attrValues', 1),
+  getAttr: markPrimop(attrs.getAttr, 'getAttr', 2),
+  hasAttr: markPrimop(attrs.hasAttr, 'hasAttr', 2),
+  mapAttrs: markPrimop(attrs.mapAttrs, 'mapAttrs', 2),
+  listToAttrs: markPrimop(attrs.listToAttrs, 'listToAttrs', 1),
+  intersectAttrs: markPrimop(attrs.intersectAttrs, 'intersectAttrs', 2),
+  catAttrs: markPrimop(attrs.catAttrs, 'catAttrs', 2),
+  groupBy: markPrimop(attrs.groupBy, 'groupBy', 2),
 
-  // String operations
-  stringLength: string.stringLength,
-  substring: string.substring,
-  concatStringsSep: string.concatStringsSep,
-  baseNameOf: string.baseNameOf,
+  stringLength: markPrimop(string.stringLength, 'stringLength', 1),
+  substring: markPrimop(string.substring, 'substring', 3),
+  concatStringsSep: markPrimop(string.concatStringsSep, 'concatStringsSep', 2),
+  baseNameOf: markPrimop(string.baseNameOf, 'baseNameOf', 1),
 
-  // Functional
-  seq: functional.seq,
-  deepSeq: functional.deepSeq,
-  abort: functional.abort,
-  throw: functional.throwFunc,
-  trace: functional.trace,
-  warn: functional.warn,
-  break: functional.breakFunc,
+  seq: markPrimop(functional.seq, 'seq', 2),
+  deepSeq: markPrimop(functional.deepSeq, 'deepSeq', 2),
+  abort: markPrimop(functional.abort, 'abort', 1),
+  throw: markPrimop(functional.throwFunc, 'throw', 1),
+  trace: markPrimop(functional.trace, 'trace', 2),
+  warn: markPrimop(functional.warn, 'warn', 2),
+  break: markPrimop(functional.breakFunc, 'break', 1),
 
-  // I/O (unimplemented)
-  import: io.importFunc,
-  scopedImport: io.scopedImport,
-  fetchClosure: io.fetchClosure,
-  fetchGit: io.fetchGit,
-  fetchTarball: io.fetchTarball,
-  fetchTree: io.fetchTree,
-  fetchurl: io.fetchurl,
-  readDir: io.readDir,
-  readFile: io.readFile,
-  readFileType: io.readFileType,
-  pathExists: io.pathExists,
-  path: io.path,
-  toFile: io.toFile,
-  toPath: io.toPath,
-  filterSource: io.filterSource,
-  findFile: io.findFile,
-  getEnv: io.getEnv,
+  import: markPrimop(io.importFunc, 'import', 1),
+  scopedImport: markPrimop(io.scopedImport, 'scopedImport', 2),
+  fetchClosure: markPrimop(io.fetchClosure, 'fetchClosure', 1),
+  fetchGit: markPrimop(io.fetchGit, 'fetchGit', 1),
+  fetchTarball: markPrimop(io.fetchTarball, 'fetchTarball', 1),
+  fetchTree: markPrimop(io.fetchTree, 'fetchTree', 1),
+  fetchurl: markPrimop(io.fetchurl, 'fetchurl', 1),
+  readDir: markPrimop(io.readDir, 'readDir', 1),
+  readFile: markPrimop(io.readFile, 'readFile', 1),
+  readFileType: markPrimop(io.readFileType, 'readFileType', 1),
+  pathExists: markPrimop(io.pathExists, 'pathExists', 1),
+  path: markPrimop(io.path, 'path', 1),
+  toFile: markPrimop(io.toFile, 'toFile', 2),
+  toPath: markPrimop(io.toPath, 'toPath', 1),
+  filterSource: markPrimop(io.filterSource, 'filterSource', 2),
+  findFile: markPrimop(io.findFile, 'findFile', 2),
+  getEnv: markPrimop(io.getEnv, 'getEnv', 1),
 
-  // Conversion (unimplemented)
-  fromJSON: conversion.fromJSON,
-  fromTOML: conversion.fromTOML,
-  toJSON: conversion.toJSON,
-  toXML: conversion.toXML,
-  toString: conversion.toString,
+  fromJSON: markPrimop(conversion.fromJSON, 'fromJSON', 1),
+  fromTOML: markPrimop(conversion.fromTOML, 'fromTOML', 1),
+  toJSON: markPrimop(conversion.toJSON, 'toJSON', 1),
+  toXML: markPrimop(conversion.toXML, 'toXML', 1),
+  toString: markPrimop(conversion.toString, 'toString', 1),
 
-  // Miscellaneous (unimplemented)
-  getContext: misc.getContext,
-  hasContext: misc.hasContext,
-  hashFile: misc.hashFile,
-  hashString: misc.hashString,
-  convertHash: misc.convertHash,
-  unsafeDiscardOutputDependency: misc.unsafeDiscardOutputDependency,
-  unsafeDiscardStringContext: misc.unsafeDiscardStringContext,
-  unsafeGetAttrPos: misc.unsafeGetAttrPos,
-  addDrvOutputDependencies: misc.addDrvOutputDependencies,
-  compareVersions: misc.compareVersions,
-  dirOf: misc.dirOf,
-  flakeRefToString: misc.flakeRefToString,
-  functionArgs: misc.functionArgs,
-  genericClosure: misc.genericClosure,
-  getFlake: misc.getFlake,
-  match: misc.match,
-  outputOf: misc.outputOf,
-  parseDrvName: misc.parseDrvName,
-  parseFlakeName: misc.parseFlakeName,
-  placeholder: misc.placeholder,
-  replaceStrings: misc.replaceStrings,
-  split: misc.split,
-  splitVersion: misc.splitVersion,
-  traceVerbose: misc.traceVerbose,
-  tryEval: misc.tryEval,
-  zipAttrsWith: misc.zipAttrsWith,
+  getContext: markPrimop(misc.getContext, 'getContext', 1),
+  hasContext: markPrimop(misc.hasContext, 'hasContext', 1),
+  hashFile: markPrimop(misc.hashFile, 'hashFile', 2),
+  hashString: markPrimop(misc.hashString, 'hashString', 2),
+  convertHash: markPrimop(misc.convertHash, 'convertHash', 2),
+  unsafeDiscardOutputDependency: markPrimop(misc.unsafeDiscardOutputDependency, 'unsafeDiscardOutputDependency', 1),
+  unsafeDiscardStringContext: markPrimop(misc.unsafeDiscardStringContext, 'unsafeDiscardStringContext', 1),
+  unsafeGetAttrPos: markPrimop(misc.unsafeGetAttrPos, 'unsafeGetAttrPos', 2),
+  addDrvOutputDependencies: markPrimop(misc.addDrvOutputDependencies, 'addDrvOutputDependencies', 2),
+  compareVersions: markPrimop(misc.compareVersions, 'compareVersions', 2),
+  dirOf: markPrimop(misc.dirOf, 'dirOf', 1),
+  flakeRefToString: markPrimop(misc.flakeRefToString, 'flakeRefToString', 1),
+  functionArgs: markPrimop(misc.functionArgs, 'functionArgs', 1),
+  genericClosure: markPrimop(misc.genericClosure, 'genericClosure', 1),
+  getFlake: markPrimop(misc.getFlake, 'getFlake', 1),
+  match: markPrimop(misc.match, 'match', 2),
+  outputOf: markPrimop(misc.outputOf, 'outputOf', 2),
+  parseDrvName: markPrimop(misc.parseDrvName, 'parseDrvName', 1),
+  parseFlakeName: markPrimop(misc.parseFlakeName, 'parseFlakeName', 1),
+  placeholder: markPrimop(misc.placeholder, 'placeholder', 1),
+  replaceStrings: markPrimop(misc.replaceStrings, 'replaceStrings', 3),
+  split: markPrimop(misc.split, 'split', 2),
+  splitVersion: markPrimop(misc.splitVersion, 'splitVersion', 1),
+  traceVerbose: markPrimop(misc.traceVerbose, 'traceVerbose', 2),
+  tryEval: markPrimop(misc.tryEval, 'tryEval', 1),
+  zipAttrsWith: markPrimop(misc.zipAttrsWith, 'zipAttrsWith', 2),
 
-  // Meta - self-reference and constants
-  builtins: create_thunk(() => builtins), // Recursive reference
+  builtins: create_thunk(() => builtins),
   currentSystem: create_thunk(() => {
     throw 'Not implemented: currentSystem';
   }),
   currentTime: create_thunk(() => Date.now()),
 
-  // Constants (special keys)
   false: false,
   true: true,
   null: null,
 
-  // Version information
   langVersion: 6,
   nixPath: [],
   nixVersion: 'NIX_JS_VERSION',

nix-js/runtime-ts/src/index.ts

@@ -7,7 +7,7 @@
 import { create_thunk, force, is_thunk, IS_THUNK } from './thunk';
 import { select, select_with_default, validate_params } from './helpers';
 import { op } from './operators';
-import { builtins } from './builtins';
+import { builtins, IS_PRIMOP } from './builtins';
 
 export type NixRuntime = typeof Nix;
 
@@ -26,6 +26,7 @@ export const Nix = {
 
   op,
   builtins,
+  IS_PRIMOP,
 };
 
 globalThis.Nix = Nix;

nix-js/src/context.rs

@@ -44,7 +44,6 @@ impl Default for Context {
             "true",
             "false",
             "null",
-
             "abort",
             "baseNameOf",
             "break",
@@ -681,10 +680,7 @@ mod test {
             Value::Const(Const::Float(3.5))
         );
 
-        assert_eq!(
-            ctx.eval("(-7) / 3").unwrap(),
-            Value::Const(Const::Int(-2))
-        );
+        assert_eq!(ctx.eval("(-7) / 3").unwrap(), Value::Const(Const::Int(-2)));
     }
 
     #[test]
@@ -700,8 +696,7 @@ mod test {
 
         // Test builtin mul with large numbers
         assert_eq!(
-            ctx.eval("builtins.mul 1000000000 1000000000")
-                .unwrap(),
+            ctx.eval("builtins.mul 1000000000 1000000000").unwrap(),
             Value::Const(Const::Int(1000000000000000000i64))
         );
     }

nix-js/src/runtime.rs

@@ -23,14 +23,17 @@ pub fn run(script: &str) -> Result<Value> {
 struct RuntimeContext<'a, 'b> {
     scope: &'a v8::PinnedRef<'a, v8::HandleScope<'b>>,
     is_thunk_symbol: Option<v8::Local<'a, v8::Symbol>>,
+    is_primop_symbol: Option<v8::Local<'a, v8::Symbol>>,
 }
 
 impl<'a, 'b> RuntimeContext<'a, 'b> {
     fn new(scope: &'a v8::PinnedRef<'a, v8::HandleScope<'b>>) -> Self {
         let is_thunk_symbol = Self::get_is_thunk_symbol(scope);
+        let is_primop_symbol = Self::get_is_primop_symbol(scope);
         Self {
             scope,
             is_thunk_symbol,
+            is_primop_symbol,
         }
     }
 
@@ -50,6 +53,23 @@ impl<'a, 'b> RuntimeContext<'a, 'b> {
             None
         }
     }
+
+    fn get_is_primop_symbol(
+        scope: &v8::PinnedRef<'a, v8::HandleScope<'b>>,
+    ) -> Option<v8::Local<'a, v8::Symbol>> {
+        let global = scope.get_current_context().global(scope);
+        let nix_key = v8::String::new(scope, "Nix")?;
+        let nix_obj = global.get(scope, nix_key.into())?.to_object(scope)?;
+
+        let is_primop_sym_key = v8::String::new(scope, "IS_PRIMOP")?;
+        let is_primop_sym = nix_obj.get(scope, is_primop_sym_key.into())?;
+
+        if is_primop_sym.is_symbol() {
+            is_primop_sym.try_cast().ok()
+        } else {
+            None
+        }
+    }
 }
 
 fn run_impl(script: &str, isolate: &mut v8::Isolate) -> Result<Value> {
@@ -127,8 +147,11 @@ fn to_value<'a, 'b>(val: v8::Local<'a, v8::Value>, ctx: &RuntimeContext<'a, 'b>)
         _ if val.is_number() => {
             let val = val.to_number(scope).unwrap().value();
             // Heuristic: convert whole numbers to Int (for backward compatibility and JS interop)
-            if val.is_finite() && val.fract() == 0.0
-               && val >= i64::MIN as f64 && val <= i64::MAX as f64 {
+            if val.is_finite()
+                && val.fract() == 0.0
+                && val >= i64::MIN as f64
+                && val <= i64::MAX as f64
+            {
                 Value::Const(Const::Int(val as i64))
             } else {
                 Value::Const(Const::Float(val))
@@ -152,7 +175,15 @@ fn to_value<'a, 'b>(val: v8::Local<'a, v8::Value>, ctx: &RuntimeContext<'a, 'b>)
                 .collect();
             Value::List(List::new(list))
         }
-        _ if val.is_function() => Value::Func,
+        _ if val.is_function() => {
+            if let Some(name) = primop_app_name(val, ctx) {
+                Value::PrimOpApp(name)
+            } else if let Some(name) = primop_name(val, ctx) {
+                Value::PrimOp(name)
+            } else {
+                Value::Func
+            }
+        }
         _ if val.is_object() => {
             if is_thunk(val, ctx) {
                 return Value::Thunk;
@@ -193,6 +224,58 @@ fn is_thunk<'a, 'b>(val: v8::Local<'a, v8::Value>, ctx: &RuntimeContext<'a, 'b>)
     matches!(obj.get(scope, is_thunk_sym.into()), Some(v) if v.is_true())
 }
 
+/// Check if a function is a primop
+fn primop_name<'a, 'b>(
+    val: v8::Local<'a, v8::Value>,
+    ctx: &RuntimeContext<'a, 'b>,
+) -> Option<String> {
+    if !val.is_function() {
+        return None;
+    }
+
+    // Use cached IS_PRIMOP symbol from context
+    let is_primop_sym = ctx.is_primop_symbol?;
+
+    let scope = ctx.scope;
+    let obj = val.to_object(scope).unwrap();
+
+    if let Some(metadata) = obj.get(scope, is_primop_sym.into())
+        && let Some(metadata_obj) = metadata.to_object(scope)
+        && let Some(name_key) = v8::String::new(scope, "name")
+        && let Some(name_val) = metadata_obj.get(scope, name_key.into())
+    {
+        Some(name_val.to_rust_string_lossy(scope))
+    } else {
+        None
+    }
+}
+
+/// Check if a primop is partially applied (has applied > 0)
+fn primop_app_name<'a, 'b>(
+    val: v8::Local<'a, v8::Value>,
+    ctx: &RuntimeContext<'a, 'b>,
+) -> Option<String> {
+    let name = primop_name(val, ctx)?;
+
+    // Get cached IS_PRIMOP symbol
+    let is_primop_sym = ctx.is_primop_symbol?;
+
+    let scope = ctx.scope;
+    let obj = val.to_object(scope).unwrap();
+
+    if let Some(metadata) = obj.get(scope, is_primop_sym.into())
+        && let Some(metadata_obj) = metadata.to_object(scope)
+        && let Some(applied_key) = v8::String::new(scope, "applied")
+        && let Some(applied_val) = metadata_obj.get(scope, applied_key.into())
+        && let Some(applied_num) = applied_val.to_number(scope)
+        && applied_num.value() > 0.0
+    {
+        Some(name)
+    } else {
+        None
+    }
+}
+
 #[test]
 fn to_value_working() {
     assert_eq!(

nix-js/src/value.rs

@@ -185,9 +185,9 @@ pub enum Value {
     /// A function (lambda).
     Func,
     /// A primitive (built-in) operation.
-    PrimOp,
+    PrimOp(String),
     /// A partially applied primitive operation.
-    PrimOpApp,
+    PrimOpApp(String),
     /// A marker for a value that has been seen before during serialization, to break cycles.
     /// This is used to prevent infinite recursion when printing or serializing cyclic data structures.
     Repeated,
@@ -201,10 +201,10 @@ impl Display for Value {
             String(x) => write!(f, r#""{x}""#),
             AttrSet(x) => write!(f, "{x}"),
             List(x) => write!(f, "{x}"),
-            Thunk => write!(f, "<CODE>"),
-            Func => write!(f, "<LAMBDA>"),
-            PrimOp => write!(f, "<PRIMOP>"),
-            PrimOpApp => write!(f, "<PRIMOP-APP>"),
+            Thunk => write!(f, "«code»"),
+            Func => write!(f, "«lambda»"),
+            PrimOp(name) => write!(f, "«primop {name}»"),
+            PrimOpApp(name) => write!(f, "«partially applied primop {name}»"),
             Repeated => write!(f, "<REPEATED>"),
         }
     }