Level 24. Maps: The Lookup Book

Imagine a dictionary, you look up a word and find its meaning. Or a phone book, you look up a name and find a number. In Hica, this is called a map.

Making a map

Use curly braces with "key": value pairs:

let ages = {"kalle": 30, "olle": 25, "lisa": 35}
println(ages)

Output: [("kalle",30),("olle",25),("lisa",35)]

Think of it like a table with two columns:

Looking things up

Use map_get to find a value by its key. It returns a maybe: because the key might not exist!

let ages = {"kalle": 30, "olle": 25}
println(ages.map_get("kalle"))    // Just(30) — found it!
println(ages.map_get("nobody"))   // Nothing — not there

Adding and changing entries

Use map_set to add a new key or change an existing one:

let ages = {"kalle": 30, "olle": 25}
let ages2 = ages.map_set("lisa", 35)    // adds lisa
let ages3 = ages2.map_set("olle", 26)   // updates olle
println(ages3.map_keys())               // ["kalle", "olle", "lisa"]

Maps don’t change, map_set gives you a new map with the change. The original stays the same.

Removing entries

let ages = {"kalle": 30, "olle": 25, "lisa": 35}
let ages2 = ages.map_remove("olle")
println(ages2.map_keys())   // ["kalle", "lisa"]

Empty maps

Use {:} to create an empty map, then build it up with map_set:

let m = {:}
let m2 = m.map_set("x", 1).map_set("y", 2)
println(m2)   // [("x",1),("y",2)]

Map tools

The secret: maps are lists!

Under the hood, a map is just a list of tuples. Pairs of (key, value). That means you can use all the list tools on maps too:

let scores = {"kalle": 95, "olle": 60, "lisa": 88}
let high = scores.filter((entry) => entry.1 >= 80)
println(high)   // [("kalle",95),("lisa",88)]

🎯 Try it: Create a map of your favourite animals and their sounds (like {"cat": "meow", "dog": "woof"}). Look up one that exists and one that doesn’t.

🎯 Try it: Start with an empty map {:} and use map_set to add three friends and their ages. Then print map_keys() and map_size().