This is IPP project 2 from 2023.
interpret.py is a script that has three arguments, help, source, and input, where the source accepts a file
with XML code. The script will perform the check and execute the individual instructions at the same time. In case of errors,
exit the program with the desired return number.
Arguments are processed first in the main function using getopt. Either help or is displayed
the program exits or switches to the interpreter. If the source or input is not specified, it will require the user to enter a path. Input will only be requested if the instruction is READ.
If you switch to the interpreter, the XML code is first processed using the ElementTree library. After that
check to see if it starts with a program tag. An instance of a class is created using a for-loop
Instruction and is stored in an array. At the same time, the XML semantics is checked when saving the instructions.
Using the for loop, all LABEL instructions are found, and an instance of the Label class is created for them
and stored in the labels field.
In the end, the instructions are just executed. The opcode is used to decide which it will be executed.
The script contains some helper functions.
file_existence - checks for existence function
select_frame – selects the desired frame according to the variable
replace – replacement of one character at a certain position of the string
arithmetic – performs the selected arithmetic operation
get_type – decides the type and returns it with a value in the correct format
modify_bool – converts bool to lowercase
modify_string – modifies the string and replaces the \xyz format with the corresponding character
do_instruction – the main function according to which it is decided what should be executed
The main part of the script is the do_instruction function, which uses a condition to decide what to do next script function.
The Instraction class defines the name, sequence number, and argument array of the instruction. Using the function
add_arg inserts a new Arg instance into args, defining the type and name. The Frame class defines
the frame_records array containing the instance of the FrameRecord class. Whenever it is performed
any instruction, the selec_frame function is used to decide which frame to work with.
This is decided using the variable name. Subsequently, using the function in Frame search_record
finds the given transformation and returns. Only if the instruction is DEFVAR is the parameter defvar
set to True.
The insert_record function inserts a new record into the frame and the modify_record function modifies an existing one
record.
Finding the value of GF@a in the global frame:
selected_frame = select_frame(args[1]) # args[1] is an instance of the class
Arg stored in the args array at the first position
record = selected_frame.search_record(args[1])
To modify the value of GF@a in the global framework:
selected_frame.modify_record(record, name, new_type, new_value)
If the argument type is var, you need to access a certain frame and only then execute a certain one
instruction (e.g. MOVE GF@a GF@b)
If args[2].arg_type == 'var':
selected_frame = selected_frame(args[2])
. . .
In the case of CREATEFRAME, a new Frame is initialized into the temp_frame variable. After execution
PUSHFRAME, the variables are renamed from TF to LF and the temp_frame variable is inserted into the array
local_frames and set to None. If it comes to POPFRAME, the same thing is done, only
the variables are renamed to TF and a pop to temp_frame is performed.
The Stack and StackData classes define how the data stack behaves. In StackData we store the type
and the name and in the Stack list stack with StackData instances. The stack contains stack_push functions
to insert new data and stack_pop to pop it out. These invoke the PUSHS and POPS instructions
In order to make jumps in the program, the sequence number of the instruction is kept in the index all the time. If there is a jump request. The labels field contains a specific Label initialization with the name on which is to be jumped, its number is taken and set as an index. The rest of the instructions work on approximately the same principle.
See LICENSE.