Hodgepodge

There are many tools to help define and execute new programming languages. (None used here.) Hopefully the following gives you a feel for the programming language creation process.

Example of My Program Language

# my first program set, x, 12 set, a, 4 set, b, 5 set, c, a + b loop abc print, " c is ", c , " x is ", x if c > x: exit set, c, c + 1 goto, abc

Language Definition

Basic rules

each statement is on a single line
each statement starts with a reserved word
reserved words are case insensitive
statements are executed one at a time in order
comments start with a '#' character and are ignored
variable names are single letters (a-z)
variable names are case insensitive
variables must be set to a value before they can be used
all numeric values are integers
strings are surrounded by double quotes
the first error stops the interpreter
"loop" marks a unique execution location
"goto" jumps to a "loop" execution location
spaces and/or a comma separates elements in a statement
an "if" statement consists of an "if" expression and an action
a colons ":" separates an "if" expression from an action
end-of-line (EOL) or end-of-file (EOF) terminates a statement

Reserved Words

exit
goto
if
loop
print
set

Math Operators

Comparisons Operators (True or False)

Click HERE for a formal (Backus Naur Form) description of my language.

Create a Lexical Analyzer?

process the complete program before executing the program
separate statements into tokens
create a list of statements
for each statement, create a list of tokens

The results of the example shown above might be:

program = [ ["set", "x", 12], ["set", "a", 10], ["set", "b", 5], ["set", "c", "a","+","b"], ["loop", "abc"], ["print", '" c is ", c," x is ",x'] ["if", "c", "<", "x", ":", "exit"] ["set", "c", "c", "+", "1"] ["goto", abc] ]

To eliminates testing for both upper and lower case convert each statement to uppercase for processing?

Replace commas with spaces and split a statement (on spaces) before processing it into tokens?

For if statements, split on colon (":") then process each part separately?

Create an Execution "Engine"?

Process each statement one at a time and perform the action.

Create a dictionary to hold variable names and their values?

Create a dictionary to hold goto locations in the program's list of statement?

FYI

The string startswith() method returns True if a string starts with a specific value, otherwise it returns False.

Common methods used to remove characters from a string.

the string replace() method
the string translate() method
string slices
regular expressions

Tools

Flex (Fast Lexical Analyzer Generator)

Flex (lexical analyser generator) (Wikipedia)

GNU Bison

GNU Bison (Wikipedia)

Compiler Construction using Flex and Bison

Win flex-bison