Booleans and Comparisons

Comparison operators

printfn "%b" (5 = 5)      // equal
printfn "%b" (5 <> 3)     // not equal
printfn "%b" (5 > 3)
printfn "%b" (5 <= 3)
printfn "%b" ("apple" < "banana")
printfn "%d" (compare 2 7)

true
true
true
false
true
-1

F# uses = for equality and <> for "not equal" — not == and !=. compare returns a negative number, zero, or a positive number.

Structural equality

= compares values, not references, for lists, tuples, arrays, records, and other F# types:

printfn "%b" ([1; 2; 3] = [1; 2; 3])
printfn "%b" ((1, "a") = (1, "a"))
printfn "%b" ([| 1; 2 |] = [| 1; 2 |])
printfn "%b" ([1; 2] < [1; 3])

true
true
true
true

Logical operators

let age = 25
let hasTicket = true

printfn "%b" (age >= 18 && hasTicket)
printfn "%b" (age < 12 || age > 65)
printfn "%b" (not hasTicket)

true
false
false

&& and || short-circuit: the right side is only evaluated if it can change the answer. not is a function, not a ! operator.

Only bool is bool

There's no "truthiness": if 1 then ... or if name then ... is a compile error. Write the comparison you mean — if count > 0 or if name <> "".

• Use =, <>, <, >, <=, >=; compare for sorting logic.
• = is structural for F# types — two lists with the same items are equal.