Bash script command result inside other variable to define prompt

Question

I would like to define a prompt which will indicate with colors whether the command executed properly and whether the command was found. As for now I have something like this but I does not work properly.

PS1="\`COMMAND_RESULT=\$\?;

if [ $COMMAND_RESULT -eq 127 ]; then echo \[\e[33m\] ---=== Command not found ===--- ;  

elif [ $COMMAND_RESULT -ne 0 ]; then echo \[\e[33m\]---=== \[\e[31m\]Oh noes, bad command \[\e[33m\]==---; 

fi\`

\n\[\e[0;37m\][\[\e[1;31m\]\@\[\e[0;37m\]] 

\[\e[0;32m\]\u\[\033[1;33m\]@\[\033[0;32m\]\h 

As for now I get this error on bash start :

-bash: [: -eq: unary operator expected
-bash: [: -ne: unary operator expected