1. A method comprising: providing a unit of a hierarchical model for display, providing the unit for display being performed by a device; receiving a function signature associated with a function represented by the unit, the function signature being input by a user, the function signature including first information for modifying one or more syntax rules used to generate the function, and receiving the function signature being performed by the device; generating, based on the unit, a first representation of the function, the first representation of the function corresponding to the function being generated using the one or more syntax rules modified based on the function signature, the first representation of the function including a first regular expression associated with a first literal expression that is included in the function when the function is generated based on the hierarchical model using the one or more syntax rules modified based on the function signature, and generating the first representation of the function being performed by the device; providing the function signature and the first representation of the function for display to the user, providing the function signature and the first representation of the function for display being performed by the device; receiving a modified function signature, the modified function signature being input by the user, the modified function signature including second information for modifying the one or more syntax rules, and receiving the modified function signature being performed by the device; generating, based on the unit, a second representation of the function, the second representation of the function corresponding to the function being generated using the one or more syntax rules modified based on the modified function signature, the second representation of the function including a second regular expression associated with a second literal expression that is included in the function when the function is generated based on the hierarchical model using the one or more syntax rules modified based on the modified function signature, and generating the second representation of the function being performed by the device; providing the modified function signature and the second representation of the function for display to the user, providing the modified function signature and the second representation of the function for display being performed by the device; receiving an input for generating code based on the hierarchical model, receiving the input being performed by the device; and generating, based on the hierarchical model, the function using the one or more syntax rules modified based on the modified function signature, the function including the second literal expression, and generating the function being performed by the device.