Description
Objective
Learn the basics of programming an ad-hoc language scanner
Assignment
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
