PLC: Workout 6 [80 points]
Due date: Friday, April 1, by midnight
About This Homework
This assignment is about writing parsers in Haskell using the alex and happy tools, which we saw in the recorded lecture for March 24th:
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Depending on how you installed Haskell, you may have alex and happy already on your computer, or else you may need to install them. To install, just run these commands in a terminal:
cabal v2-install alex
cabal v2-install happy
How to Turn In Your Solution
Follow this link to create your repo on Github Classrooms for workout4:
https://classroom.github.com/a/_2NvQ9k3
If you work with a partner, please add to your repo a file called partners.txt, and list your name and your partner’s name there. Both of you should submit your solution: each partner pushes it to their github repo.
How To Get Help
You can post questions in the Discussions section of ICON.
You are also welcome to come to our office hours. See the course’s Google Calendar, linked from the github page for the class, for times and Zoom links for office hours. You can also find these on the “Zoom links, office hours” page under “Pages” on ICON:
https://uiowa.instructure.com/courses/179776/pages/office-hours
No reading this week.
2 Regular expressions [50 points]
The subdirectory RegexProblems contains exercises for writing a lexical specification, to be pro- cessed by alex. Within that subdirectory, run
cabal v1-build
in a terminal or command shell to generate and compile the lexer. (Cabal takes care of invoking alex for you.) You can run the lexer on sample input like this:
cabal v1-run p0-yes.txt
Your job is to add regular expressions to the file Tokens.x. A solution is provided for you already as an example: p0 matches one ’a’ followed by zero or more ’b’s. You will just add your regular expressions in a similar way as the example one, to Tokens.x. (All your solutions can be added to just this one Tokens.x file and it should work correctly.) Positive testcases are provided in files with names like p0-yes.txt, and a couple of negative ones (that should cause your lexer to report an error) in files like p4-no.txt. Note that lexers are expected to return a sequence of tokens, and so input files that have matching strings one after the other will return lists of length greater than 1 of matches. You need to implement the following [8 points each]:
• p1: match zero or more ’c’s followed by one or more ’d’s.
• p2: match one or more ’e’ or ’f’ characters.
• p3: match a single lowercase character (’a’ through ’z’), then match zero or more characters that are either lowercase characters or numeric digits (’0’ through ’9’).
• p4: match strings quoted by either single or double quotes, containing zero or more characters that are either upper or lowercase letters or space (you have to write \ to indicate a space in alex’s format) .
• p5: match any nonempty sequence of X and Y characters where there is an even number (including 0) of X characters.
You will find the expected output for all the yes tests in expected-output.txt.
3 Grammars [40 points]
Each of the following problems has its own subdirectory. You will only need to modify the produc- tions part of the Grammar.y file in that directory (Main.hs, Tokens.x, and other files do not need to be modified). Again, compile using cabal v1-build, and test using cabal v1-run yes1.tp. Note that for both grammars, the lexer I am providing for you (in Tokens.x in each directory) already deals with whitespace. So your Grammar.y files only need to deal with the tokens listed at the top of the Grammar.y file. [20 points each]
• Grammar1: add productions to Grammar1/Grammar.y to recognize simple Haskell type ex- pressions built from the unit type (), parentheses, and right-associative arrow types. Positive testcases are given in yes1.tp, etc. Expected output is in expected-output.txt.
• Grammar2: add productions to Grammar2/Grammar.y to recognize a simple fragment of an imperative programming language, as follows:
– a Prog is a list of FunCalls, where each FunCall is followed by a semicolon
– a FunCall is either a simple identifier (i.e., variable name like “x”), or else a function call, which consists of an identifier, then a left parenthesis, then a comma-separated list of zero or more FunCalls, and then a right parenthesis.
For example, a simple Prog is: a;
f(b,g(c));
The FunCalls are a and f(b,g(c)). Notice that the second FunCall is nested. Positive
testcases are again yes1.prog, etc., and expected output is again in expected-output.txt.
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