Language basics

27 steps in 9 sets of Scala.

Scala runs functional programming on the JVM at industrial scale: Spark, Kafka, and half the big-data stack are written in it, and it compiles to the same bytecode Java does while saying twice as much per line. Scala 3 is the dialect here — the braceless, indentation-based syntax with enums, extension methods, and top-level definitions that made the language feel a decade younger.

This tour covers the everyday core: vals and type inference, expressions everywhere (if and match return values), methods and lambdas, the immutable collections and their map/filter/fold toolkit, case classes with copy, enums, Option and Either instead of null and exceptions, and traits with extension methods. The encore ships complete programs. Every seed compiles under scalac -Werror with unused-checking on, and the encore runs start to finish.

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Values & types

val & varA ferry seat count held in val bindings, with one var for the number that really changes.
Type inferenceThe compiler reads Int, Double, String and List types off the values you write.
String interpolationThree interpolators: s for values, f for formatted output, raw for untouched escapes.

Expressions

if as an expressionif/else evaluates to a value in Scala, so it can be assigned straight to a val.
match basicsMatching on plain values, with alternatives, guards, and a catch-all.
for loopsThree shapes of for: over a collection, over .indices, and with two generators.

Functions

Defining methodsdef with typed parameters and a return type, first as an expression and then as an indented body.
Default & named argumentsParameters that carry defaults, and calls that name their arguments instead of ordering them.
Lambdas & function valuesFunction literals, the _ shorthand, and a method that takes a function as a parameter.

Collections

ListsA tide log held in a List, extended at both ends and read back safely.
MapsA seed drawer as a Map, read two different ways and updated without mutation.
SetsA set of studied chess openings, tested for membership and combined against a rival repertoire.

Transformations

Map and filterBakery order counts run through map and filter, alone and chained.
FoldingCrate weights collapsed to a total, then to a string and to a Map.
For comprehensionsOrchard rows turned into new collections with for and yield.

Case classes & enums

Case classesA Lighthouse record with generated printing and equality, taken apart by a match.
Copy updatesKiln firings revised with copy, which builds a new value and leaves the old one alone.
EnumsA signal enum matched exhaustively, and a second enum whose cases carry data.

Option & Either

OptionScala's answer to null: a value that is either there or admits it is not.
Chaining OptionsTwo dependent lookups and a test, with no null check anywhere.
Either for validationEither keeps the reason a value was rejected, where a bare Option cannot.

Traits & extensions

TraitsA trait fixes what every shape must answer and writes the shared part once.
Extension methodsAdding methods to Int and String without owning either type.
Objects and companionsAn object is a namespace with one instance; a companion is where constructors go.

Encore

word_freq.scalaA whole report: normalize a passage, count its words, rank and print them.
grade_report.scalaPer-student averages, letter grades and a class summary from an inline roster.
temp_stats.scalaOne week of high temperatures as a table of stats and a bar chart.