Ligo Lang "unbound variable fail"

Question

When I try to compile this contract https://github.com/stove-labs/nft.stove-labs.com/blob/master/src/contracts/nft.ligo using the command

ligo compile-contract nft.ligo main > nft.tz

per the steps in the docs here https://nft.stove-labs.com/ I get the following output:

ligo: generated. unbound variable fail:  {"variable":"fail","environment":"- E[s -> record[contractOwner -> address , nfts -> (TO_Map (nat,record[catColor -> string , catName -> string , owner -> address]))] , action -> record[nftToMint -> record[catColor -> string , catName -> string , owner -> address] , nftToMintId -> nat] , arguments -> ( record[nftToMint -> record[catColor -> string , catName -> string , owner -> address] , nftToMintId -> nat] * record[contractOwner -> address , nfts -> (TO_Map (nat,record[catColor -> string , catName -> string , owner -> address]))] )]\tT[action -> sum[Burn -> record[nftToBurnId -> nat] , Mint -> record[nftToMint -> record[catColor -> string , catName -> string , owner -> address] , nftToMintId -> nat] , Transfer -> record[destination -> address , nftToTransfer -> nat]] , actionBurn -> record[nftToBurnId -> nat] , actionTransfer -> record[destination -> address , nftToTransfer -> nat] , actionMint -> record[nftToMint -> record[catColor -> string , catName -> string , owner -> address] , nftToMintId -> nat] , storageType -> record[contractOwner -> address , nfts -> (TO_Map (nat,record[catColor -> string , catName -> string , owner -> address]))] , nfts -> (TO_Map (nat,record[catColor -> string , catName -> string , owner -> address])) , nft -> record[catColor -> string , catName -> string , owner -> address] , nftId -> nat]\n]","location":"generated"}

Answer 1

Use the function failwith with a string argument describing the error, and cast it to the desired type if necessary (for example, if you are in an expression), like so: failwith ("My error"); or (failwith ("My error") : my_expected_type)

Note the parentheses around the string, as failwith is a function, not a keyword.