Programming Languages F28PL,Introductory Lecture 1 st Semester - PowerPoint PPT Presentation

Programming Languages F28PL,Introductory Lecture 1 st Semester 2019/20 1 / 38

Programming Languages F28PL ◮ Languages ◮ OCaml (functional), weeks 1-4 ◮ Python (scripting), weeks 6-9 ◮ Prolog (logic), weeks 10-11 ◮ Lectures ◮ Thursdays, 11:15, JW2 ◮ Thursday, 15:15, JW2 ◮ Fridays, 15:15, PG G.01 ◮ Labs ◮ Mondays, 11:15, EM 2.50 (not this week) 2 / 38

F28PL Programming Languages course starts next lecture (Thursday morning). This introductory lecture: ◮ Property based tests ◮ Running OCaml code ◮ GitLab setup for this course ◮ Using git at command line 3 / 38

Unit Testing ◮ In SD3 we used unit tests to check implementations assertEquals(12, add(10, 2), "10 + 2 is 12"); ◮ code under test: add method ◮ inputs: 10 and 2 ◮ expected result: 12 ◮ validates if code results in the expected output ◮ checks piece of code is correct More tests: assertEquals(0, add(0, 0), "0 + 0 is 0"); assertEquals(2, add(2, 0), "2 + 0 is 2"); ... ◮ Time consuming to write many tests ◮ How many unit tests until we have confidence in add(..) ? 4 / 38

Declaring Properties of Code ◮ “Any number N added to 0 is N” ◮ “Any number N multiplied by 0 is 0” ◮ “Reversing a list then reversing it again returns the original list” ◮ “Multiplying an even number by 2 returns an even number” ◮ “After sorting an integer list the smallest value is the 1st element of the returned list” ◮ “After performing upheap on a binary tree the smallest value is the root of the tree” (priority queues from SD3) ◮ “After adding N unique words to a trie there are N words in the trie” (from SD3) QuickCheck is a framework that generates tests for these properties. Then runs the tests to find counterexamples. 5 / 38

Property Testing with OCaml (* adding a list to an empty list returns empty list e.g. seqadd [1;2;3] [] = [] *) let seqadd_empty1 = QCheck . Test .make ~name:"seqadd_empty1" ~count:10000 QCheck .(make integer_sequence_gen) ( fun list1 -> seqadd list1 [] = []);; ◮ Generator: integer_sequence_gen generates integer lists ◮ Generator bound to the list1 variable ◮ Property: seqadd list1 [] = [] QuickCheck will generate lots of tests: seqadd [1;5;4;...] [] = [] seqadd [9;2;8;... [] = [] seqadd [8;8;3;... [] = [] 6 / 38

Generators for test inputs OCaml qcheck library has generators: val small_nat : int arbitrary val int_range : int -> int -> int arbitrary val pos_float : float arbitrary val bool : bool arbitrary val char : char arbitrary val string_gen_of_size : int Gen .t -> char Gen .t -> string arbitrary val list : ' a arbitrary -> ' a list arbitrary val pair : ' a arbitrary -> ' b arbitrary -> ( ' a * ' b) arbitrary val oneof : ' a arbitrary list -> ' a arbitrary ... OCaml’s QuickCheck API: https://c-cube.github.io/qcheck/0.9/qcheck-core/QCheck/ https://c-cube.github.io/qcheck/0.9/qcheck-core/QCheck/Gen/ 7 / 38

Generators for test inputs User defined OCaml generators: (* integer sequence generator of 100 elements *) let integer_sequence_gen = QCheck . Gen .(list_size (return 100) nat);; (* zeros sequence generator of 100 elements *) let zeros_gen = QCheck . Gen .(list_size (return 100) (return 0));; (* from the OCaml coursework *) type complex_number = CI of int * int ;; (* complex number generator *) let complex_number_gen = ( QCheck . Gen .map ( fun (x,y) -> CI (x,y)) QCheck . Gen .(pair small_nat small_nat));; 8 / 38

Property Testing with OCaml (* adding 0 to each element in a sequence result in the same sequence, and hence the input sequence should be the same as the output sequence e.g. seqadd [1;2;3] [0;0;0] => [1;2;3] *) let seqadd_zeros = QCheck . Test .make ~name:"seqadd_zeros" ~count:1000 QCheck .(make ~print:show_sequence ( Gen .pair integer_sequence_gen zeros_gen)) ( fun (seq,zeros) -> seqadd seq zeros = seq);; 9 / 38

Property Testing with OCaml ◮ seqmult multiplies every list element by a constant ◮ sum sums up all elements in a list Property: “for all integer lists, if we multiply every element by 0 then sum the resulting list is zero” . let seqmult_zeros = let sum = List .fold_left (+) 0 in QCheck . Test .make ~name:"seqmult_zeros" ~count:1000 QCheck .(make ~print:show_sequence ( Gen .pair integer_sequence_gen zeros_gen)) ( fun (seq,zeros) -> sum (seqmult seq zeros) = 0);; 10 / 38

Property Testing with OCaml Property: “For all lists of generated integer lists, bubble sort and quick sort functions output the same list” let bubble_quick_equiv = QCheck . Test .make ~name:"bubble_quick_equiv" ~count:100 QCheck .(make ( Gen .list Gen .small_nat)) ( fun xs -> bubble_sort xs = quick_sort xs);; ◮ xs comes from (Gen.list Gen.small_nat) ◮ 100 tests generated ◮ Property: bubble_sort xs = quick_sort xs 11 / 38

Property Testing and Functional Programming ◮ Unit testing common for imperative and object oriented languages ◮ Property based testing almost exclusive to functional languages ◮ Why? In (pure) functional languages, the output of a function is exclusively determined by its input values. Quick Check property testing frameworks generate and run 100s/1000s/millions of tests. Imperative/OO languages have global/hidden state: calling the same function/method twice might return a different result. A unit test is ran only once. 12 / 38

Running OCaml Interpreter (ocaml): Read–eval–print loop (REPL) ◮ run functions with different inputs ◮ ask what type values/functions have ◮ slower performance > ocaml OCaml version 4.05.0 # #use "ocaml_part1.ml" ;; 13 / 38

Running OCaml Compiler (ocamlc): compile to native code ◮ can’t test functions interactively ◮ code is optimised ◮ fast performance OCaml file has a main function: let main = print_int (add 2 3) ;; Compile it: > ocamlc -o part1 ocaml_part1.m > ./part1 5 14 / 38

◮ Text editors ◮ Emacs ◮ Tuareg mode: https://github.com/ocaml/tuareg ◮ Vim ◮ Merlin: https://github.com/ocaml/merlin ◮ gedit ◮ VSCode ◮ vscode-reasonml: https: //github.com/reasonml-editor/vscode-reasonml ◮ Compilers ◮ ocamlc ◮ Interpreters ◮ ocaml ◮ utop ◮ improved ocaml : line editing, history, real-time and context sensitive completion, colors. ◮ opam install dune ◮ https://github.com/ocaml-community/utop 15 / 38

Structure of Ocaml projects ◮ lib directory for implementation ◮ test directory for tests - lib |-> SequenceArithmetic.ml -> dune - test |-> SequenceArithmeticTests.ml -> dune - dune-project https://gitlab-student.macs.hw.ac.uk/f28pl-2019-20/ f28pl-2019-20-ocaml-coursework/tree/master/ sequence-arithmetic 16 / 38

Test files ◮ Ocaml coursework has unit tests and property based tests Unit tests: (* test seqadd on two non-empty lists *) let seqadd_test2 _test_ctxt = assert_equal [7;5;6] (seqadd [2;3;5] [5;2;1]);; Property tests: (* adding an integer list to list of 0's should return the list e.g. seqadd [1;2;3] [0;0;0] => [1;2;3] *) let seqadd_zeros = QCheck . Test .make ~name:"seqadd_zeros" ~count:1000 QCheck .(make ~print:show_sequence ( Gen .pair integer_sequence_gen zeros_gen)) ( fun (seq,zeros) -> seqadd seq zeros = seq);; 17 / 38

Running OCaml Tests > cd sequence-arithmetic/ > dune clean > dune runtest --profile release ... Ran: 12 tests in: 0.11 seconds. FAILED: Cases: 12 Tried: 12 Errors: 5 Failures: 7 Skip: 0 Todo: 0 Timeouts: 0. Test driven development.. the goal: Ran: 12 tests in: 2.28 seconds. OK 18 / 38

GitLab for F28PL https://gitlab-student.macs.hw.ac.uk/f28pl-2019-20 19 / 38

Versioning metadata ◮ Who made changes? ◮ e.g. Rob Stewart � R.Stewart@hw.ac.uk � ◮ What files did they change? ◮ e.g. lib/arithmetic.ml ◮ Where in the file did they make the change? ◮ e.g. line 287 of lib/server.ml ◮ When did they make the change? ◮ e.g. 11:04, Friday 19th October 2018. ◮ Why did they make a change? ◮ e.g. to fix single-sign-on login ◮ Who is affected by the change? ◮ e.g. Paul to add login property based tests 20 / 38

Visualising git History ◮ GitLab website (click “N commmits” for history) ◮ git gui ( gitk command) 21 / 38

Fork repository 22 / 38

Clone your fork 23 / 38

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Check status (Note: these slides are adapted from 3 rd year course.) $ git status On branch master nothing to commit, working directory clean 26 / 38

$ vim README $ git status On branch master Untracked files: (use "git add <file>..." to include in what will be committed) README nothing added to commit but untracked files present (use "git add" to track) 27 / 38

Track new files $ git add README $ git status On branch master Changes to be committed: (use "git reset HEAD <file>..." to unstage) new file: README 28 / 38

Staging modified files $ git status On branch master Changes to be committed: (use "git reset HEAD <file>..." to unstage) new file: README Changes not staged for commit: (use "git add <file>..." to update what will be committed) (use "git checkout -- <file>..." to discard changes in working directory) modified: benchmarks.rb 29 / 38