Learn the basics of programming an ad-hoc language scanner
Build the start of an ad hoc scanner to handle a simple language. The output for the scanner will be a list, and in order, of the type of token, a comma, and the actual value of the token (the token and the lexeme).
This must be written in Java.
If you create more than one Java file, compress all of your files into a single file for uploading.
You must use file input. Pick up the source code file name from the command line. Exit gracefully with an error message if the input file does not exist.
Write the output to the screen.
There is no error checking required of file names OTHER than to ensure if they are present – your program will not be given an illegal file name when testing.
There is no guarantee of whitespace except where required to separate tokens. A line feed is a form of whitespace. There will not be any tab characters in the source code.
An <id token is a string of alphabetic characters starting with an upper or lower case ‘a’-‘z’, followed by either an upper or lower case ‘a’-‘z’ or ‘0’-‘9’ (standard identifier rules without the underscore character). An <id cannot be one of the reserve words in the grammar.
A <number can be either an integer or a floating point value. A floating point value WILL have at least one digit both in front and after a decimal point.
A <rel_op token is either a <, , <=, =, ==, or !=
The <assign token, the assignment operator, is the equal sign (“=”).
The “reserved” words in the grammar are all lowercase and casespecific. They include: input, print, begin, end, if, and Their respective tokens are <input, <print, <begin, <end, <if, and <else.
A # symbol indicates a comment. Ignore the remainder of the current physical line. This will not generate a token.
If your program encounters text that is not a valid token, write out an
<error token and the invalid text (not the remainder of the file). Stop processing the input file after dealing with an error.
For example, if the input file contains:
#sample “source code” for simple language min = 0 input a input b if a < b begin min = a end else min = b
print min
your output should contain:
<id, min
<assign, =
<number, 0
<input, input
<id, a
<input, input
<if, if
<id, a
<rel_op, <
<id, b
<begin, begin
<id, min
<assign, =
<id, a
<end, end
<else, else
<id, min
<assign, =
<id, b
<print, print
<id, min
