Fix: Mismatched Types String and Byte in Golang

In Golang, the "invalid operation: new_str str[i 1] (mismatched types string and byte)" error occurs when attempting to concatenate a string and a byte. Explicit conversions are required to resolve this issue.

The problem arises in the code snippet provided:

for i < len(str) - 1 {
    new_str = new_str   str[i   1]
    i = i   1
}

To fix this, we need to convert str[i 1] to a string using the string() function:

for i < len(str) - 1 {
    new_str = new_str   string(str[i   1])
    i = i   1
}

A similar issue occurs in line 24. To resolve it, we apply the same conversion:

return f(g(str))   string(str[0])

After these fixes, the code will operate correctly and concatenate strings properly.