1. Values, not a shopping list of commands

bend src/01-values.bend

Its entire computation is:

def main() -> U32:
  (6 * 7 : U32)

Expect 42. The body produces a value; there is no ordinary statement-level return here. We will use return later inside monadic do blocks.

U32 is an unsigned 32-bit numeric type. The : U32 on the arithmetic expression tells Bend which operations to use: multiplication here is U32.mul. Keep the spaces around operators. Bend does very little type inference, so even a typed function often needs an annotation on an operator expression.

Other literal families include 1.5 for F32, 3n for Nat, 'c' for Char, and "hello" for String. Nat represents natural numbers and will also give us a structurally shrinking counter.

Haskell companion: (6 * 7 :: Word32) is a close comparison, using Word32 from Data.Word. Haskell's numeric literals and operators use type classes and inference; (6 * 7 :: Integer) chooses a different, arbitrary-precision type. Bend's (a * b : U32) explicitly selects operations for U32. Do not bring Integer assumptions to a U32 party.

Try it: replace multiplication with addition, then add parentheses to compute ((6 + 1 : U32) * 7 : U32). Predict the result before running it.