Bindings & signatures in Haskell

A trail profile written as top-level bindings, each with its own type signature.

-- Every top-level binding gets its own type signature above it.
module TrailProfile where

trailName :: String
trailName = "Ridge Loop"

trailMiles :: Double
trailMiles = 8.4

restStops :: Int
restStops = 3

-- GHC would infer Double here on its own; the signature pins it down
-- and documents the binding for the next reader.
milesPerLeg :: Double
milesPerLeg = trailMiles / fromIntegral (restStops + 1)

summary :: String
summary = trailName ++ " runs " ++ show trailMiles ++ " miles"

How it works

1. trailName :: String and trailMiles :: Double sit directly above the values they describe.
2. restStops is an Int, so fromIntegral widens it before the division.
3. A comment notes that GHC would infer the Double for milesPerLeg without any help.

Keywords and builtins used here

• Double
• Int
• String
• milesPerLeg
• module
• restStops
• summary
• trailMiles
• trailName
• where

The run, in numbers

Lines

19

Characters to type

488

Tokens

56

Three-star pace

80 tpm

At the three-star pace of 80 tokens a minute, this run takes about 42 seconds.

Type this snippet

Step 1 of 3 in Values & types, step 1 of 27 in Language basics.

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