CS152 Project Phase 1: Lexical Analyzer Generation Using flex

Start Date: 06/21/21
Due Date: 06/28/21
Grade Weight: 10% of total course grade
This project can be completed either individually or in pairs (with at most 1 other person)


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 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

The following tasks will need to be performed to complete this phase of the project.
  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.