Pipes & Composition

Relanote uses pipes for data transformation, making code read left-to-right like music flows.

The Pipe Operator

The pipe operator |> passes the left value as the argument to the right function:

scale Major = { R, M2, M3, P4, P5, M6, M7 }

let melody = | <1> <3> <5> <3> |

; Without pipes
reverse (transpose P5 melody)

; With pipes (much clearer!)
melody |> transpose P5 |> reverse

Chaining Transformations

Build complex transformations step by step:

scale Major = { R, M2, M3, P4, P5, M6, M7 }

let melody = | <1> <3> <5> <3> |

let result = melody
  |> transpose P5              ; Transpose up a fifth
  |> repeat 2                  ; Repeat twice

result

Function Composition

Use >> to compose functions without applying them:

; Create a reusable transformation
let myTransform = transpose P5 >> reverse >> repeat 2

; Apply to different melodies
melody1 |> myTransform
melody2 |> myTransform

Partial Application

Many functions support partial application:

let upFifth = transpose P5      ; Partially applied
let doubled = repeat 2

melody |> upFifth |> doubled

Common Pipe Patterns

Transform and Combine

scale Major = { R, M2, M3, P4, P5, M6, M7 }

let theme = | <1> <3> <5> <3> |

let variation = theme
  |> transpose P4
  |> reverse

let combined = theme ++ variation

combined

Conditional Transformation

let loud = melody |> volume 1.0
let soft = melody |> volume 0.4

if energetic then loud else soft

Lambda Expressions

Create inline functions with \:

scale Major = { R, M2, M3, P4, P5, M6, M7 }

let melody = | <1> <2> <3> |

; Add an octave to each note
let higher = melody |> map (\note -> note + P8)

higher

Pipeline Best Practices

1. Read left-to-right: Each step should logically follow the previous
2. Name intermediate results: For complex pipelines, use let bindings
3. Keep functions pure: Avoid side effects in pipe chains
4. Compose for reuse: Create named transformations for common patterns

scale Major = { R, M2, M3, P4, P5, M6, M7 }

; Good: Clear, named stages
let melody = | <1> <3> <5> |
let transposed = melody |> transpose P5
let final = transposed |> repeat 2

; Also good: Fluent chain for simple cases
| <1> <3> <5> | |> transpose P5 |> repeat 2