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+# Bogumił Kamiński, 2022
+
+# Codes for chapter 4
+
+# Code for listing 4.1
+
+import Downloads
+Downloads.download("https://raw.githubusercontent.com/" *
+                   "sidooms/MovieTweetings/" *
+                   "44c525d0c766944910686c60697203cda39305d6/" *
+                   "snapshots/10K/movies.dat",
+                   "movies.dat")
+
+# Code for string interpolation examples
+
+x = 10
+"I have $x apples"
+
+"I have \$100."
+"I have $100."
+
+# Code for multiline strings
+
+Downloads.download("https://raw.githubusercontent.com/\
+                    sidooms/MovieTweetings/\
+                    44c525d0c766944910686c60697203cda39305d6/\
+                    snapshots/10K/movies.dat",
+                   "movies.dat")
+
+"a\
+ b\
+ c"
+
+# Code for raw strings
+
+"C:\my_folder\my_file.txt"
+
+raw"C:\my_folder\my_file.txt"
+
+# Code for listing 4.2
+
+movies = readlines("movies.dat")
+
+# Code for section 4.2
+
+movie1 = first(movies)
+
+movie1_parts = split(movie1, "::")
+
+supertype(String)
+supertype(SubString{String})
+
+# Code for section 4.3
+
+movie1_parts[2]
+
+rx = r"(.*) \((\d{4})\)$"
+
+m = match(rx, movie1_parts[2])
+
+m[1]
+m[2]
+
+parse(Int, m[2])
+
+# Code for listing 4.3
+
+function parseline(line::String)
+    parts = split(line, "::")
+    m = match(r"(.*) \((\d{4})\)", parts[2])
+    return (id=parts[1],
+            name=m[1],
+            year=parse(Int, m[2]),
+            genres=split(parts[3], "|"))
+end
+
+# Code for parsing one line of movies data
+
+record1 = parseline(movie1)
+
+# Code for listing 4.4
+
+codeunits("a")
+codeunits("ε")
+codeunits("∀")
+
+# Codes for different patterns of string subsetting
+
+word = first(record1.name, 8)
+
+record1.name[1:8]
+
+for i in eachindex(word)
+    println(i, ": ", word[i])
+end
+
+codeunits("ô")
+
+codeunits("Fantômas")
+
+isascii("Hello world!")
+isascii("∀ x: x≥0")
+
+word[1]
+word[5]
+
+# Code for section 4.5
+
+records = parseline.(movies)
+
+genres = String[]
+for record in records
+    append!(genres, record.genres)
+end
+genres
+
+using FreqTables
+table = freqtable(genres)
+sort!(table)
+
+years = [record.year for record in records]
+has_drama = ["Drama" in record.genres for record in records]
+drama_prop = proptable(years, has_drama, margins=1)
+
+# Code for listing 4.5
+
+using Plots
+
+plot(names(drama_prop, 1), drama_prop[:, 2], legend=false,
+     xlabel="year", ylabel="Drama probability")
+
+# Code for section 4.6.1
+
+s1 = Symbol("x")
+s2 = Symbol("hello world!")
+s3 = Symbol("x", 1)
+
+typeof(s1)
+typeof(s2)
+typeof(s3)
+
+Symbol("1")
+
+:x
+:x1
+
+:hello world
+:1
+
+# Code for section 4.6.2
+
+supertype(Symbol)
+
+:x == :x
+:x == :y
+
+# Code for listing 4.6
+
+using BenchmarkTools
+str = string.("x", 1:10^6)
+symb = Symbol.(str)
+@benchmark "x" in $str
+@benchmark :x in $symb
+
+# Code for section 4.7
+
+using InlineStrings
+s1 = InlineString("x")
+typeof(s1)
+s2 = InlineString("∀")
+typeof(s2)
+sv = inlinestrings(["The", "quick", "brown", "fox", "jumps",
+                    "over", "the", "lazy", "dog"])
+
+# Code for listing 4.7
+
+using Random
+using BenchmarkTools
+Random.seed!(1234);
+s1 = [randstring(3) for i in 1:10^6]
+s2 = inlinestrings(s1)
+
+# Code for analyzing properties of InlineStrings.jl
+
+Base.summarysize(s1)
+Base.summarysize(s2)
+
+@benchmark sort($s1)
+@benchmark sort($s2)
+
+# Code for listing 4.8
+
+open("iris.txt", "w") do io
+    for i in 1:10^6
+        println(io, "Iris setosa")
+        println(io, "Iris virginica")
+        println(io, "Iris versicolor")
+    end
+end
+
+# Code for section 4.8.2
+
+uncompressed = readlines("iris.txt")
+
+using PooledArrays
+compressed = PooledArray(uncompressed)
+
+Base.summarysize(uncompressed)
+Base.summarysize(compressed)
+
+# Code for section 4.8.3
+
+compressed.invpool
+compressed.pool
+
+compressed[10]
+compressed.pool[compressed.refs[10]]
+
+Base.summarysize.(compressed.pool)
+
+v1 = string.("x", 1:10^6)
+v2 = PooledArray(v1)
+Base.summarysize(v1)
+Base.summarysize(v2)