Units of measure in F#

kg and jar ride the type system; wrong units will not compile.

// Units of measure ride the type system: kg + km will not compile.
[<Measure>] type kg
[<Measure>] type jar

let harvest = 12.4<kg>
let perJar = 0.34<kg/jar>

// The division cancels units: kg over kg/jar leaves jars.
let jars = harvest / perJar
printfn "Jars this pull: %.0f" (float jars)

let combined = harvest + 3.1<kg>
printfn "With the late frames: %.1f kg" (float combined)
// let broken = harvest + 2.0<jar>  // the compiler stops this line

How it works

1. [<Measure>] type kg declares a unit with no runtime cost.
2. 0.34<kg/jar> types a rate; division cancels the units.
3. The commented line shows what the compiler refuses.

Keywords and builtins used here

• float
• jar
• kg
• let
• type

The run, in numbers

Lines

14

Characters to type

449

Tokens

83

Three-star pace

60 tpm

At the three-star pace of 60 tokens a minute, this run takes about 83 seconds.

Type this snippet

Step 2 of 3 in Signatures & laziness, step 23 of 27 in Language basics.

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