# Moc -r file.mo err, why?

**URL:** <https://forum.dfinity.org/t/moc-r-file-mo-err-why/7111>\
**Category:** Developers\
**Tags:** Functional-Programming\
**Created:** [September 10, 2021, 2:36am UTC](https://forum.dfinity.org/t/moc-r-file-mo-err-why/7111 "2021-09-10T02:36:40Z")\
**Posts on this page:** 2\
**Page:** 1

<div class="post-metadata">

**Author:** ![goose](https://sea1.discourse-cdn.com/flex023/user_avatar/forum.dfinity.org/goose/32/6164_2.png) [@goose](https://forum.dfinity.org/u/goose)\
**Post date:** [September 10, 2021, 2:36am UTC](https://forum.dfinity.org/t/moc-r-file-mo-err-why/7111/1 "2021-09-10T02:36:40Z")

</div>

```
       let a = Principal.fromActor(this);
        Debug.print(debug_show(id, Principal.toText(a)));

```

show\_val: {  
assetRequest = func;  
authorize = func;  
balanceOf = func;  
balanceOfInsecure = func;  
cycle = func;  
getAuthorized = func;  
getAuthorizedInsecure = func;  
getContractInfo = func;  
getContractInfoInsecure = func;  
getEventCallbackStatus = func;  
getMetadata = func;  
getTotalMinted = func;  
http\_request = func;  
http\_request\_streaming\_callback = func;  
init = func;  
isAuthorized = func;  
isAuthorizedInsecure = func;  
listAssets = func;  
mint = func;  
ownerOf = func;  
ownerOfInsecure = func;  
postupgrade = func;  
preupgrade = func;  
queryProperties = func;  
setEventCallback = func;  
tokenChunkByID = func;  
tokenChunkByIDInsecure = func;  
tokensByID = func;  
tokensByIDInsecure = func;  
transfer = func;  
updateContractOwners = func;  
updateProperties = func;  
wallet\_receive = func;  
writeStaged = func  
} : Principal

```
        /Users/ipfs/.cache/dfinity/versions/0.7.2/base/Principal.mo:15.57-15.58: internal error, "Assert_failure mo_values/show.ml:88:4"
```

---

<div class="post-metadata">

**Author:** ![claudio](https://sea1.discourse-cdn.com/flex023/user_avatar/forum.dfinity.org/claudio/32/322_2.png) [@claudio](https://forum.dfinity.org/u/claudio)\
**Post date:** [September 10, 2021, 5:14pm UTC](https://forum.dfinity.org/t/moc-r-file-mo-err-why/7111/2 "2021-09-10T17:14:25Z")

</div>

moc -r runs the interpreter which, unfortunately, does not implement all features of Motoko. I believe Principal.toText is probably one of them.