Implement string-length function.
Implement string-ref function.
Add to chack the string length.
Implement make-string function.
Implement the case insensitive string functions.
Fix an error of the shadowing the existing binding.
Define the type signature of the trapError function.
Suppress the warning of the do-notation statement discard a result.
Fix the non-exhaustive pattern matches by adding the error handling code.
Fix the non-exhaustive pattern matches by adding the error handling code.
This is the part that is leaking the previous fix.
Fix the misuse of the otherwise keyword.
Fix an issue that the strBoolBinopCi always return True or False.
Remove the unused definitions.
Fix the issue of shadowing the existing binding by renaming.
Add the type signature to the binary operation functions.
The type variable 'a' in the extractValue is changed to 'String' because of adding the Left pattern.