CS152 Project Phase 1: Lexical Analyzer Generation Using flex

Overview

For this first part of the class project, you will use the flex tool to generate a lexical analyzer for a high-level source code language called "MINI-L". The lexical analyzer should take as input a MINI-L program, parse it, and output the sequence of lexical tokens associated with the program.

[The MINI-L language is described in detail here.]
[The required output format for your lexical analyzer is described here.]

Flex

Flex is a tool for generating lexical analyzers. Lexical analyzers scan text (a sequence of characters) and look for lexical patterns in the text. Flex requires an input file specifying a description for a lexical analyzer to generate. From this description, flex will automatically create a C program for you (called lex.yy.c) that will perform the lexical analysis.

In our department, flex is installed and can be used on "bolt".

[A brief introduction to flex can be found here.]
[For detailed information on flex here.]

For the complete flex documentation, run the command info flex from bolt.

Detailed Requirements

1. Write the specification for a flex lexical analyzer for the MINI-L language. For this phase of the project, your lexical analyzer need only output the list of tokens identified from an inputted MINI-L program.
   Example: write the flex specification in a file named mini_l.lex.
2. Run flex to generate the lexical analyzer for MINI-L using your specification.
   Example: execute the command flex mini_l.lex. This will create a file called lex.yy.c in the current directory.
3. Compile your MINI-L lexical analyzer. This will require the -lfl flag for gcc.
   Example: compile your lexical analyzer into the executable lexer with the following command: gcc -o lexer lex.yy.c -lfl. The program lexer should now be able to convert an inputted MINI-L program into the corresponding list of tokens.

Example Usage

Suppose your lexical analyzer is in the executable named lexer. Then for the MINI-L program fibonacci.min, your lexical analyzer should be invoked as follows:

cat fibonacci.min | lexer

The list of tokens outputted by your lexical analyzer should then appear as they do here. The tokens can be printed to the screen (standard out).

Another example: for program mytest.min, the outputted tokens should look like this.
For program primes.min, the outputted tokens should look like this.