Expression Syntax

Complete reference for the RMT Compose expression language.

Overview

Expressions are JavaScript-like formulas that define note properties. They compile to binary bytecode for efficient evaluation.

Constants

Integer

javascript

new Fraction(440)    // 440/1
new Fraction(0)      // 0/1
new Fraction(-5)     // -5/1

Fraction

javascript

new Fraction(3, 2)   // 3/2
new Fraction(5, 4)   // 5/4
new Fraction(-1, 4)  // -1/4

Large Numbers

For very large or precise values:

javascript

new Fraction(123456789, 987654321)

Arbitrary precision is supported via BigInt internally.

References

BaseNote Reference

javascript

module.baseNote.getVariable('frequency')
module.baseNote.getVariable('startTime')
module.baseNote.getVariable('duration')
module.baseNote.getVariable('tempo')
module.baseNote.getVariable('beatsPerMeasure')

Note Reference

javascript

module.getNoteById(1).getVariable('frequency')
module.getNoteById(5).getVariable('startTime')
module.getNoteById(10).getVariable('duration')

The note ID must be a positive integer matching an existing note.

Arithmetic Operations

Addition

javascript

a.add(b)

// Examples
new Fraction(1).add(new Fraction(2))  // 3
module.baseNote.getVariable('startTime').add(new Fraction(1))

Subtraction

javascript

a.sub(b)

// Examples
new Fraction(5).sub(new Fraction(2))  // 3
module.getNoteById(3).getVariable('startTime').sub(new Fraction(0.5))

Multiplication

javascript

a.mul(b)

// Examples
new Fraction(3).mul(new Fraction(2))  // 6
module.baseNote.getVariable('frequency').mul(new Fraction(3, 2))  // Fifth

Division

javascript

a.div(b)

// Examples
new Fraction(6).div(new Fraction(2))  // 3
new Fraction(60).div(module.findTempo(module.baseNote))  // Beat duration

Negation

javascript

a.neg()

// Examples
new Fraction(5).neg()  // -5

Power

javascript

a.pow(b)

// Examples
new Fraction(2).pow(new Fraction(3))     // 8 (2³)
new Fraction(2).pow(new Fraction(1, 2))  // √2 ≈ 1.414
new Fraction(2).pow(new Fraction(1, 12)) // 12-TET semitone

WARNING

Non-integer exponents produce irrational results (SymbolicPower). These display with the ≈ prefix.

Lookup Functions

Find Tempo

javascript

module.findTempo(module.baseNote)

Walks the inheritance chain to find the tempo value. Usually returns BaseNote's tempo.

Find Measure Length

javascript

module.findMeasureLength(module.baseNote)

Computes measure duration based on tempo and beatsPerMeasure.

Chaining Operations

Operations can be chained:

javascript

module.baseNote.getVariable('frequency')
  .mul(new Fraction(3, 2))
  .mul(new Fraction(5, 4))

// Equivalent to: baseFreq × 3/2 × 5/4 = baseFreq × 15/8

Precedence

Standard mathematical precedence applies:

Parentheses (implicit in method chaining)
Power (.pow())
Negation (.neg())
Multiplication/Division (.mul(), .div())
Addition/Subtraction (.add(), .sub())

Common Patterns

Relative Frequency

javascript

// Perfect fifth above BaseNote
module.baseNote.getVariable('frequency').mul(new Fraction(3, 2))

// Major third above another note
module.getNoteById(1).getVariable('frequency').mul(new Fraction(5, 4))

// Octave below
module.baseNote.getVariable('frequency').div(new Fraction(2))

Sequential Timing

javascript

// Start when previous note ends
module.getNoteById(prev).getVariable('startTime')
  .add(module.getNoteById(prev).getVariable('duration'))

Beat-Relative Duration

javascript

// One beat
new Fraction(60).div(module.findTempo(module.baseNote))

// Two beats
new Fraction(60).div(module.findTempo(module.baseNote)).mul(new Fraction(2))

// Half beat
new Fraction(60).div(module.findTempo(module.baseNote)).mul(new Fraction(1, 2))

TET Intervals

javascript

// 12-TET semitone
new Fraction(2).pow(new Fraction(1, 12))

// 12-TET major third (4 semitones)
new Fraction(2).pow(new Fraction(4, 12))

// Simplified: 4/12 = 1/3
new Fraction(2).pow(new Fraction(1, 3))

Error Conditions

Syntax Errors

javascript

// Missing parenthesis
new Fraction(3, 2.mul()  // Error

// Unknown method
new Fraction(3).multiply(2)  // Error (should be .mul())

// Invalid fraction
new Fraction(3.5, 2)  // Error (must be integers)

Reference Errors

javascript

// Non-existent note
module.getNoteById(999).getVariable('frequency')  // Error

// Invalid variable name
module.baseNote.getVariable('pitch')  // Error (should be 'frequency')

Circular Dependencies

javascript

// Note 1 references Note 2
note1.frequency = module.getNoteById(2).getVariable('frequency')

// Note 2 references Note 1 - Error!
note2.frequency = module.getNoteById(1).getVariable('frequency')

Best Practices

Use meaningful references: Reference notes by their role, not arbitrary IDs
Keep expressions readable: Break complex expressions into multiple notes
Simplify fractions: Use new Fraction(1, 2) not new Fraction(2, 4)
Test incrementally: Verify each expression before building on it
Use BaseNote for transposition: Reference BaseNote for root-relative notes

Expression Syntax ​

Overview ​

Constants ​

Integer ​

Fraction ​

Large Numbers ​

References ​

BaseNote Reference ​

Note Reference ​

Arithmetic Operations ​

Addition ​

Subtraction ​

Multiplication ​

Division ​

Negation ​

Power ​

Lookup Functions ​

Find Tempo ​

Find Measure Length ​

Chaining Operations ​

Precedence ​

Common Patterns ​

Relative Frequency ​

Sequential Timing ​

Beat-Relative Duration ​

TET Intervals ​

Error Conditions ​

Syntax Errors ​

Reference Errors ​

Circular Dependencies ​

Best Practices ​

See Also ​

Expression Syntax

Overview

Constants

Integer

Fraction

Large Numbers

References

BaseNote Reference

Note Reference

Arithmetic Operations

Addition

Subtraction

Multiplication

Division

Negation

Power

Lookup Functions

Find Tempo

Find Measure Length

Chaining Operations

Precedence

Common Patterns

Relative Frequency

Sequential Timing

Beat-Relative Duration

TET Intervals

Error Conditions

Syntax Errors

Reference Errors

Circular Dependencies

Best Practices

See Also