ligo/gitlab-pages/docs/language-basics/boolean-if-else.md

id	title
boolean-if-else	Booleans and Conditionals

Booleans

The type of a boolean value is bool. Here is how to define a boolean value:

const a : bool = True   // Notice the capital letter
const b : bool = False  // Same.

let a : bool = true
let b : bool = false

let a : bool = true;
let b : bool = false;

Comparing Values

In LIGO, only values of the same type can be compared. Moreover, not all values of the same type can be compared, only those with comparable types, which is a concept lifted from Michelson. Comparable types include, for instance, int, nat, string, tez, timestamp, address, etc. As an example of non-comparable types: maps, sets or lists are not comparable: if you wish to compare them, you will have to write your own comparison function.

Comparing Strings

const a : string = "Alice"
const b : string = "Alice"
const c : bool = (a = b) // True

let a : string = "Alice"
let b : string = "Alice"
let c : bool = (a = b) // true

let a : string = "Alice";
let b : string = "Alice";
let c : bool = (a == b); // true

Comparing numbers

const a : int  = 5
const b : int  = 4
const c : bool = (a = b)
const d : bool = (a > b)
const e : bool = (a < b)
const f : bool = (a <= b)
const g : bool = (a >= b)
const h : bool = (a =/= b)

let a : int  = 5
let b : int  = 4
let c : bool = (a = b)
let d : bool = (a > b)
let e : bool = (a < b)
let f : bool = (a <= b)
let g : bool = (a >= b)
let h : bool = (a <> b)

let a : int  = 5;
let b : int  = 4;
let c : bool = (a == b);
let d : bool = (a > b);
let e : bool = (a < b);
let f : bool = (a <= b);
let g : bool = (a >= b);
let h : bool = (a != b);

Comparing tez

💡 Comparing tez values is especially useful when dealing with an amount sent in a transaction.

const a : tez  = 5mutez
const b : tez  = 10mutez
const c : bool = (a = b) // False

let a : tez  = 5mutez
let b : tez  = 10mutez
let c : bool = (a = b) // false

let a : tez  = 5mutez;
let b : tez  = 10mutez;
let c : bool = (a == b); // false

Conditionals

Conditional logic enables forking the control flow depending on the state.

type magnitude is Small | Large // See variant types.

function compare (const n : nat) : magnitude is
  if n < 10n then Small (Unit) else Large (Unit) // Unit is needed for now.

You can run the compare function defined above using the LIGO compiler like this:

ligo run-function
gitlab-pages/docs/language-basics/boolean-if-else/cond.ligo compare 21n'
# Outputs: Large (Unit)

When the branches of the conditional are not a single expression, as above, we need a block:

if x < y then
  block {
    const z : nat = x;
    x := y; y := z
  }
else skip;

As an exception to the rule, the blocks in a conditional branch do not need to be introduced by the keywor block, so, we could have written instead:

if x < y then {
  const z : nat = x;
  x := y; y := z
}
else skip;

type magnitude = Small | Large // See variant types.

let compare (n : nat) : magnitude =
  if n < 10n then Small else Large

You can run the compare function defined above using the LIGO compiler like this:

ligo run-function
gitlab-pages/docs/language-basics/boolean-if-else/cond.mligo compare 21n'
# Outputs: Large

type magnitude = | Small | Large; // See variant types.

let compare = (n : nat) : magnitude =>
  if (n < 10n) { Small; } else { Large; };

You can run the compare function defined above using the LIGO compiler like this:

ligo run-function
gitlab-pages/docs/language-basics/boolean-if-else/cond.religo compare 21n'
# Outputs: Large