CS 453 Homework Assignment #2 — Haskell warmup

The Tutorial

The Assignment

In this homework assignment you will be writing four Haskell "helper" functions and two separate main programs. The "helper" functions will be used to implement the two main programs.

The prototypes and descriptions for the "helper" functions are as follows:

    -- Returns true if the given String starts with the "while" string 
    -- and false otherwise.
    startsWithWhile :: String -> Bool

    -- Given a string, returns the number of instances of the "while" string.
    countWhile :: String -> Int

    -- Given a list of strings such as ["hello","5","goodbye","6","hello","1"]
    -- creates a list that pairs every other key string with the integer value
    -- for the following number string 
    -- (e.g., [("hello",5),("goodbye",6),("hello",1)].
    findKeyValPairs :: [String] -> [(String,Int)]

    -- Given an existing dictionary stored as a list of key,value pairs,
    -- and a new key,value pair, add the value to the existing value for
    -- the given key or put the given key,value pair into the dictionary.
    -- For example,
    --      updateDict [("hello",5)] ("goodbye",6)
    -- should evaluate to
    --      [("hello",5),("goodbye",6)]
    -- As another example
    --      updateDict [("hello",5),("goodbye",6)] ("goodbye",4)
    -- should evaluate to
    --      [("hello",5),("goodbye",10)]
    updateDict :: [(String,Int)] -> (String,Int) -> [(String,Int)]

The "startsWithWhile" and "countWhile" helper functions should be in the file hw2main1/src/Util.hs. The file should have the following structure:

    module Util where

    startsWithWhile :: String -> Bool
    -- TODO: write the implementation here

    countWhile :: String -> Int
    -- TODO: write the implementation here

    module Main where

    import Util
    
    main = do
        -- TODO: write implementation here

The main1 program will read from stdin and print to stdout a count of all instances of the string "while". Assuming you use stack and call the stack project "hw2main1", you should be able to run the program as follows:

    stack exec hw2main1 < infile.txt > outfile.txt

The main2 program will read an input filename from the command line and an output file from the command line. The input file will have keywords and integer counts of those keywords listed on separate lines. For example,

    hello
    5
    goodbye
    6
    hello
    12

    hello,17
    goodbye,6

    stack exec hw2main2 infile.txt outfile.txt

Getting Started

Read and work through the tutorial examples.

Optional Tool: SPOJ

Unlike programming assignments where you are almost entirely responsible for developing a test suite for your compilers, for this homework assignment we have provided a contest in SPOJ that tests all of the examples in the tutorial and all of the "helper" functions and main programs in HW2. Therefore, you can fully test all of your functions on SPOJ before submitting your HW2. See Using SPOJ to test HW2 problems for more details.

Groups for HW2

There should be NO groups for HW2. Everyone should do HW2 by themselves. MOSS is able to compare Haskell programs.

You can create a github repository for HW2 by going to the HW2 assignment in the github classroom for cs453.

Submitting the Assignment

• Make sure your code works on lectura.
• You should have two stack projects: one for hw2main1 and the other for hw2main2. Each of those projects will have a src/Main.hs file. In addition, each of them should have a src/Util.hs file where you will put the helper functions for that particular main program. From the directory where each of the stack projects lives, execute the following:

    cp hw2main1/src/Main.hs hw2main1.hs
    cp hw2main1/src/Util.hs hw2util1.hs
    cp hw2main2/src/Main.hs hw2main2.hs
    cp hw2main2/src/Util.hs hw2util2.hs
  
    tar cvf HW2.tar hw2main1.hs hw2util1.hs hw2main2.hs hw2util2.hs
    

• Submit your HW2.tar file using turnin on lectura.

    turnin cs453HW2 HW2.tar
    

Grading

Late Policy