Added CSCI-344 final review.

blogContent/posts/programming/CSCI-334-Final-Review.md

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+A quick review for CSCI-344 (Programming Language Concepts)
+
+
+# Ch #1 What are Programming Languages
+
+## Types
+
+### Imperative
+
+Most common type of language
+
+- Von Neumann (Fortran, Basic, C)
+- Object-oriented (SmallTalk, java)
+- Scripting (perl, python, basic)
+
+### Declarative
+
+- Functional (Scheme, ML)
+- Logical (Prolog)
+
+## Compilation vs Interpretation
+
+Interpretation is more flexible and gives better diagnostics for debugging.
+Compilation provides better performance.
+Often there is no clear cut difference between compilation and interpretation because many languages like java and python do a mix of the both.
+
+### Compilation
+
+![](media/plcfinal/compilation.png)
+
+### Interpretation
+
+![](media/plcfinal/interpretation.png)
+
+
+### Mixed
+
+![](media/plcfinal/mixed.png)
+
+
+### Compilation Overview
+
+![](media/plcfinal/compOverview.png)
+
+
+# Ch #2 Parsing
+
+## Context-Free Grammars
+
+We use CFGs to produce a parse tree from tokens.
+
+![](media/plcfinal/cfgEx.png)
+
+## LL Grammar
+
+LL(1) grammar means that it is left right left most derivation parsing with one token look ahead.
+In practice we would use a stack to keep track what we expect to see.
+In this approach we would build the tree top down.
+The LL parsing algorithm uses FIRST/FOLLOW/PREDICT tables.
+
+Ex grammar:
+
+![](media/plcfinal/ll.png)
+
+## LR Grammar
+
+LR (Left to right right most derivation) builds the tree bottom up and is almost always table driven.
+
+
+## Scanning
+
+A scanner is responsible for tokenizing the source, removing comments, saving text of identifiers, and saving line locations for error messages.
+A scanner is most naturally represented as a DFA (Deterministic Finite Automaton).
+
+![](media/plcfinal/scanner.png)
+
+# Ch #10 Object Oriented
+
+Three major OO Components:
+
+- Encapsulation
+- Inheritance
+- Dynamic method binding
+
+Strict terms for OO lang: everything is an object, inheritance, dynamic method binding.
+Since java has primitives, it is not a true OO language. 
+
+
+## Small Talk
+
+Started as a thesis project in the 1960's, has been noted as being one of the best OO language historically. 
+
+Basic coding examples on class-inheritance and constructors may be on exam.
+
+### Syntax
+
+Excessively uses parenthesis.
+Method calls are in the form: (function:: object parameter1 parameter 2).
+NOTICE: the colons in the function name represents how many parameters it has.
+Also, there are no commas between parameters.
+
+
+
+Basic example class. 
+
+```scheme
+(class Shape Object
+    (perimeter area) ; class-level parameters
+    
+    ;constructor
+    (class-method initalize::shape (per ar)
+        (init::shape (new self) per ar)
+    )
+
+    (method init::shape (per ar)
+        (setPerimeter: self per)
+        (setArea: self ar)
+        self
+    )
+
+    (method getPerimeter () 
+        perimeter
+    )
+    
+    (method getArea () 
+        area
+    )
+
+    (method setArea: (a)
+        (set area a)
+    )
+
+    (method setPerimeter: (p)
+        (set perimeter p)
+    )
+)
+
+(val shape1 (initalize::shape Shape 12 5))
+
+; area
+(getArea shape1)
+(setArea: shape1 88)
+(getArea shape1)
+```
+
+
+Example with inheritance:
+
+```scheme
+(class Circle Shape
+    (radius)
+
+    (class-method initalize:circle (rad)
+        (init:circle (new self) rad)
+    )
+
+    (method init:circle (rad)
+        (setRadius: self rad)
+        self
+    )
+
+    (method setRadius: (rad)
+        (set radius rad)
+        (setArea: self (computeArea self))
+        (setPerimeter: self (computePerimeter self))
+    )
+
+    (method getRadius ()
+        radius
+    )
+
+    (method computeArea ()
+        (* 
+            (asFloat (/ 22 7)) 
+            (asFloat (squared radius))
+        )
+    )
+
+    (method computePerimeter ()
+        (* 
+            (asFloat 2) 
+            (* 
+                (asFloat (/ 22 7)) 
+                (asFloat radius)
+            )
+        )
+    )
+)
+
+
+(val circle1 (initalize:circle Circle 5))
+(getRadius circle1)
+(getArea circle1)
+(getPerimeter circle1)
+
+(setRadius: circle1 6)
+(getRadius circle1)
+(getArea circle1)
+(getPerimeter circle1)
+```
+
+# Ch #3: Name, Scope, and Binding
+
+A name is a identifier. A binding links a name to an item.
+Scope is simply when a binding is active.
+
+
+# Binding
+
+Binding typically happens at two times:
+- Static: before run time
+- Dynamic: at run time.
+
+The earlier the binding the greater efficiency you have. The later the binding the greater flexibility you have.
+
+Static scope rules use the structure of the program.
+Dynamic scope rules depends on the current state of the program so, the function call sequences can change which bindings are active.
+
+# Lifetime
+
+Key events:
+
+- creation of object
+- creation of binding
+- references to variables (uses binding)
+- deactivation of binding (leave function stack)
+- reactivation of bindings
+- destruction of bindings
+- destruction of object
+
+If object out lives its binding it's garbage.
+If binding out lives its object it's a dangling reference.
+
+# Ch #4 Semantic Analysis
+
+The role of semantic analysis is to enforce semantic rules and generate a syntax tree(decorate the parse tree).
+To do this we use a attribute grammar.
+
+ex attribute grammar:
+
+![](media/plcfinal/attributeGrammar.png)
+
+## S-Grammar:
+
+Only uses synthesized attributes: the grammar above.
+
+![](media/plcfinal/sgrammar.png)
+
+## L-Grammar:
+
+A l attribute depends on things above them or besides them in the parse tree.
+
+![](media/plcfinal/lgrammar.png)
+
+## Action Routines
+
+Functions used to interleave the parser.
+
+
+# Ch #11: Functional Programming
+
+Examples:
+- Lisp
+- Scheme
+- FP
+- ML
+- Haskell
+
+Key Ideas:
+- everything is done by composing functions
+- no mutable state
+- no side effects
+- just produces a answer/result
+
+Necessary Features:
+- first class and high-order functions (takes in/returns functions)
+- polymorphism
+- powerful list functionality
+- structured function returns
+- fully general aggregates
+- garbage collection
+
+Since there is no state, it heavily relies on recursion to replace iteration.
+
+## Scheme
+
+Not purely functional because it has some imperative stuff like assignment, I/O, sequencing and IO
+
+Scheme scopes:
+- let: calculates all RHS and then assign, can't use prior ones
+- let*: evaluates and then assigns
+- letrec: evaluates and then assign, this will loop back to fill in missing pieces as they are declared
+
+
+### Scheme Examples:
+
+Note: cdr is tail of list and car is the first element in the list.
+
+```scheme
+; Computes length of list
+(define (length lst)
+  (if (null? lst)
+     0
+     (+
+       1
+       (length (cdr lst))
+     )
+  )
+)
+
+
+; determines if something is in the list
+; returns:
+;   1 if true(in list)
+;   0 if not in list
+(define (inList lst n)
+ (if (null? lst)
+     0
+     (if (= n (car lst))
+         1
+         (inList (cdr lst) n)
+     )
+ ) 
+)
+
+; finds the sum of the list
+(define (sumList lst)
+  (if (null? lst)
+      0 ; empty list
+      (+
+         (car lst)
+         (sumList (cdr lst))
+      )
+  )
+)
+```
+
+# Ch #6: Control Flow
+
+Types of iteration:
+- Sequencing: specifies a linear ordering on statements
+- Selection: selects a section of code ie: if statements
+- Iteration: for loops, iterates over a well-defined set
+- Concurrency
+- Exception Handling
+- Non-determinacy
+
+
+Orthogonality: feature can be used in any combination and the meaning is consistent.
+
+
+# Ch #7: Data Types
+
+
+Data types are a collection of values from a "domain".
+Data types specify the structure of the data and a collection of well-defined operations you can perform on that type.
+Data types are useful for implicit context and so that we can avoid meaningless operations.
+
+Strong typing is when language prevents on data that is not appropriate.
+
+Static typing is strong typing that the compiler can do.
+
+Orthogonality: no restriction on how a collection of features can be combined: like python lists.
+
+## Type Systems
+
+A type system has rules for the following:
+- type equivalence
+- type compatibility: can type A be used in context of type B
+- type inference: type of expression given its operands types
+
+## Type Checking
+
+Two major types:
+- Structural Equivalence: based on memory layout to determine if same -- can result in unintended equivalencies
+- Name equivalence: based on declaration type -- most common
+
+## Coercion
+
+When an expression of one type is used in the context of another. Implicit coercion is when the language does it. 
+Explicit is when the programmer does it (Casting).
+
+# Ch #12: Logical Programming
+
+Logical programming is based on predicate calculus.
+
+Important concepts:
+- Axioms: facts assumed true in knowledge base
+- Theorems: things that are provably true
+- Hypotheses: things or queries we would like to prove
+- ATOM is a constant like a number
+
+Within logical languages, statements can be written many ways.
+Logical languages are good for people but bad for people.
+Prolog uses backwards chaining to prove things true mathematically.
+
+
+A horn clause contains a HEAD and a BODY, sll statements must be in this term. The head is a single term, but, the body can be a list of terms.
+
+## Prolog Ex
+
+```Prolog
+path(b, f, 6).
+path(g, f, 3).
+path(e, g, 2).
+path(h, g, 4).
+
+
+% makes paths bi-directional
+biPath(A, B, Y) :- path(A, B, Y).
+biPath(A, B, Y) :- path(B, A, Y).
+
+% X is starting point
+% Y is ending point
+% P is a list of the points on the final path if one exists
+% N is the distance between X and Y if one exists
+
+% rule for terminal
+solveV(X, X, [X], 0, V).
+
+% recursively build out path
+solveV(A, B, [A|P], N, V) :- biPath(A, C, CC),
+                             \+member(C, V),
+                             solveV(C, B, P, CCC, [C|V]),
+                             N is CC + CCC.
+
+% expand given definition to helper function
+solve(A, B, P, N) :- solveV(A, B, P, N, [A]).
+
+% ex test runs in interpreter
+solve(h, c, P, N).
+solve(a, e, P, N).
+solve(g, c, P, N).
+solve(a, a, P, N).
+solve(g, h, P, N).
+```
+
+# Ch #8: Composite Types
+
+Types:
+- Records (Structures)
+- Arrays
+- Strings
+- Pointers
+- Lists
+- File I/O
+
+## Garbage Collection
+
+Problem with reference counter for garbage collection:
+
+![](media/plcfinal/counter.png)
+
+Mark and Sweep solution:
+
+- Garbage collector walks heap basically marks everything as useless
+- starts at outside pointers marking everything it can get to as useful
+-walks the heap again placing useless items in the free queue.
+
+
+## Pointers
+
+### Tombstones
+
+Costly way of dealing with pointers references.
+This will create an additional object to maintain the pointer.
+
+![](media/plcfinal/rip.png)
+
+
+### Lock and Keys
+
+Makes sure that pointers and pointe contains the same lock value before you dereference the object.
+Note: this does not prevent attempting to use memory outside of your block resulting in a seg fault.
+
+![](media/plcfinal/lock.png)
+
+
+# Ch #13: Erlang
+
+Approaches to parallel programming:
+- Synchronized access to shared memory
+- Message passing between processes (slower)
+
+Race conditions are whe the result depends on the order of the thread actions.
+Usually due to bad synchronization but, not always bad.
+
+Synchronization ensures that events in different processes happen in a desired order.
+Mutual exclusion: only one can access at a time.
+Condition synchronization: wait until some condition is true.
+
+Spin lock - busy-wait mutual exclusion, they waste processing cycles. Semaphores: widely used and uses a scheduler-based methods.
+Monitors are used to note who is in a critical region.
+
+## Erlang
+
+Syntax of erlang is very similar to prolog with its pattern matching.
+Erlang relies on message passing for concurrency.
+Each process contains a "mailbox" where it can receive messages from.
+You process by listening for a message of a specific format: ie you can choose to ignore certain messages for a period of time.
+
+### Examples
+
+![](media/plcfinal/erlang.png)
+
+```Erlang
+%%%-------------------------------------------------------------------
+%%% @author Jeffery Russell
+%%% @doc
+%%% PLC assignment 4
+%%% @end
+%%% Created : 16. Nov 2019
+%%%-------------------------------------------------------------------
+-module(prog4).
+-author("jeff").
+
+%% API
+-export([start/0, bank/0, client/0]).
+
+% helper function to spawn a specific amount
+% of clients
+spawn_client(N) when N >= 1 ->
+  io:fwrite("Spawning a client\n"),
+  spawn(prog4, client, []),
+  spawn_client(N -1);
+
+spawn_client(_) ->
+  io:fwrite("Spawned all clients\n").
+
+% start with random account balance between 2k-3k
+% receives message {clientid, number}
+% negatives removes from bank, positives add
+% returns {<client_id>, balance}
+bank() ->
+  Balance = rand:uniform(1000) + 1999,
+  io:format("Bank balance starting at: ~w~n", [Balance]),
+  Client_count = rand:uniform(7) + 2,
+  Client_left = 1,
+  spawn_client(Client_count),
+  loop(Balance, Client_count, Client_left).
+
+% main bank loop which listens for messages and
+% processes them
+loop(Balance, Client_count, Client_left) ->
+  receive
+    %io:format("Bank now has ~w", [balance])
+    {CLIENT_ID, balance} ->
+      io:fwrite("~w Requested Balance from the bank\n", [CLIENT_ID]),
+      CLIENT_ID ! {Balance},
+      loop(Balance, Client_count, Client_left);
+    {CLIENT_ID, NUMBER} ->
+      if
+        Balance + NUMBER >= 0 ->
+          CLIENT_ID ! {NUMBER, Balance + NUMBER, successful},
+          loop(Balance + NUMBER, Client_count, Client_left);
+        true ->
+          CLIENT_ID ! {NUMBER, Balance, failed},
+          loop(Balance, Client_count, Client_left)
+      end;
+    goodbye ->
+      if
+        Client_left == Client_count ->
+          io:format("Bank is closing with balance ~w`\n", [Balance]);
+        true ->
+          loop(Balance, Client_count, Client_left + 1)
+      end
+  end.
+
+
+% helper function to fetch and print balance of the bank
+client_fetch_balance() ->
+  bank_pid ! {self(), balance},
+  receive
+    {Balance} ->
+      io:format("~w recieved the balance of ~w from the bank~n", [self(), Balance])
+  end.
+
+
+% client process loop
+% if loop is increment of 5, it requests balance of bank
+% withdraws a random amount of money from mank
+% and prints the bank's response
+% after each withdrawl, it will sleep
+client_loop(LoopUntil, CurrentIndex) ->
+  if
+    CurrentIndex rem 5 == 0 ->
+      client_fetch_balance();
+    true -> pass
+  end,
+
+  if
+    LoopUntil == CurrentIndex ->
+      bank_pid ! goodbye,
+      io:format("~w Client Finished\n", [self()]);
+    true ->
+      bank_pid ! {self(), 100-rand:uniform(199) },
+
+      receive
+        {Amount, Balance, Suc} ->
+          io:format("~w recieved the balance of ~w from the bank after a ~w transation request of ~w~n", [self(), Balance, Suc, Amount])
+      end,
+      timer:sleep(rand:uniform(1000) + 499),
+      client_loop(LoopUntil, CurrentIndex + 1)
+  end.
+
+
+% creates random amount of clients
+client() ->
+  Nums = rand:uniform(10) + 9,
+  client_loop(Nums, 0).
+
+
+% spawns the bank
+start() ->
+  register(bank_pid, spawn(prog4, bank, [])).
+```
+
+# Ch #14: Scripting Languages
+
+
+Common Characteristics:
+- both batch and interactive use
+- easy to write high level expressions
+- simple scoping rules
+- flexible dynamic typing
+- easy access to other programs
+- sophisticated pattern matching and string manipulation
+- high level data types
+
+Often used to glue together other programs.
+
+Need to know bash on the exam.
+
+## Bash
+
+### Shall Parameters
+
+- "$#" is the number of parameters passed
+- "$0" is name of the script and its location in filesystem
+- "$1" is the first command line parameter. Goes up till 9
+- "$*" single word of all the parameters
+- "$@" array of all the parameters
+
+ex:
+
+```bash
+if [ $# -eq 3 ];
+then
+    if [ -f $1 ]
+    then
+        if [ -f $2 ]
+        then
+            encode_message $1 $2 $3
+        else
+            echo "File $2 does not exist"
+        fi
+    else
+        echo "File $1 does not exist"
+    fi
+else
+    echo "Usage:"
+    echo "     encoder.sh <plane_text_file> <secret_key_file> <encoded_file>"
+fi
+```
+
+### Files
+
+```bash
+    while read line || [ -n "$line" ];
+    do
+        for word in $line
+        do
+            echo "$word"
+        done
+    done < "$1"
+```
+
+### Comparisons
+
+Numbers:
+
+- "-eq" equal
+- "-ge" greater than or equal
+- "-le" less than or equal
+- "-ne" not equal
+- "-gt" greater
+- "-lt" less
+
+ex:
+
+```bash
+[n1 -eq n2]
+```
+
+
+Strings:
+
+- "=" equal
+- "!=" not equal
+- "-n" length is greater than zero
+- "-z" length is equal to zero
+
+ex:
+
+```
+[ s1 - s2 ]
+[ -n s1 ]
+```
+
+Files:
+
+- "-d" path is a directory
+- "-f" is a file
+- "-e" file name exists
+- "-r" check of read permission
+- "-s" file has length greater than 0
+- "-w" write permission
+- "-x" execution permission
+
+ex:
+```bash
+[ -d fname ]
+```
+
+### Control Flow
+
+#### If Statements
+
+```bash
+if [ expression ];
+then
+    statements
+elif [ expression ];
+then
+    statements
+else
+    statements
+fi
+```
+
+
+#### Switch Statements
+
+```bash
+case $var in
+	val1)
+		statements
+        ;;
+	val2)
+		statements
+        ;;
+	*)
+		statements
+        ;;
+	esac
+```
+
+### Math
+
+To do math you math like this:
+
+```bash
+echo "$((124+23))"
+
+# or like this:
+
+VALOR=$[124+23]
+
+# or with let
+
+let X=124+23
+```
+
+
+### Functions
+
+Functions exist in bash.
+
+```bash
+#!/bin/bash
+hello()
+{
+    echo "Woeie"
+}
+hello  # no parenthesis needed when calling
+
+# you can also declare functions with the keyword
+
+function check()
+{
+    return 42
+}
+```
+
+