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Add scale-generator exercise (#50)
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‎config.json

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"prerequisites": [],
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"difficulty": 3
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},
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{
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"slug": "scale-generator",
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"name": "Scale Generator",
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"uuid": "c9d72016-4314-4086-8642-1e9e006e19ab",
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"practices": [],
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"prerequisites": [],
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"difficulty": 3
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},
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{
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"slug": "spiral-matrix",
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"name": "Spiral Matrix",

‎exercises/practice/scale-generator/.docs/instructions.md

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# Instructions
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## Chromatic Scales
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Scales in Western music are based on the chromatic (12-note) scale.
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This scale can be expressed as the following group of pitches:
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> A, A♯, B, C, C♯, D, D♯, E, F, F♯, G, G♯
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A given sharp note (indicated by a ♯) can also be expressed as the flat of the note above it (indicated by a ♭) so the chromatic scale can also be written like this:
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> A, B♭, B, C, D♭, D, E♭, E, F, G♭, G, A♭
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The major and minor scale and modes are subsets of this twelve-pitch collection.
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They have seven pitches, and are called diatonic scales.
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The collection of notes in these scales is written with either sharps or flats, depending on the tonic (starting note).
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Here is a table indicating whether the flat expression or sharp expression of the scale would be used for a given tonic:
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| Key Signature | Major | Minor |
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| ------------- | --------------------- | -------------------- |
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| Natural | C | a |
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| Sharp | G, D, A, E, B, F♯ | e, b, f♯, c♯, g♯, d♯ |
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| Flat | F, B♭, E♭, A♭, D♭, G♭ | d, g, c, f, b♭, e♭ |
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Note that by common music theory convention the natural notes "C" and "a" follow the sharps scale when ascending and the flats scale when descending.
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For the scope of this exercise the scale is only ascending.
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### Task
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Given a tonic, generate the 12 note chromatic scale starting with the tonic.
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- Shift the base scale appropriately so that all 12 notes are returned starting with the given tonic.
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- For the given tonic, determine if the scale is to be returned with flats or sharps.
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- Return all notes in uppercase letters (except for the `b` for flats) irrespective of the casing of the given tonic.
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## Diatonic Scales
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The diatonic scales, and all other scales that derive from the chromatic scale, are built upon intervals.
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An interval is the space between two pitches.
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The simplest interval is between two adjacent notes, and is called a "half step", or "minor second" (sometimes written as a lower-case "m").
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The interval between two notes that have an interceding note is called a "whole step" or "major second" (written as an upper-case "M").
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The diatonic scales are built using only these two intervals between adjacent notes.
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Non-diatonic scales can contain other intervals.
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An "augmented second" interval, written "A", has two interceding notes (e.g., from A to C or D♭ to E) or a "whole step" plus a "half step".
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There are also smaller and larger intervals, but they will not figure into this exercise.
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### Task
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Given a tonic and a set of intervals, generate the musical scale starting with the tonic and following the specified interval pattern.
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This is similar to generating chromatic scales except that instead of returning 12 notes, you will return N+1 notes for N intervals.
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The first note is always the given tonic.
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Then, for each interval in the pattern, the next note is determined by starting from the previous note and skipping the number of notes indicated by the interval.
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For example, starting with G and using the seven intervals MMmMMMm, there would be the following eight notes:
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| Note | Reason |
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| ---- | ------------------------------------------------- |
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| G | Tonic |
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| A | M indicates a whole step from G, skipping G♯ |
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| B | M indicates a whole step from A, skipping A♯ |
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| C | m indicates a half step from B, skipping nothing |
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| D | M indicates a whole step from C, skipping C♯ |
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| E | M indicates a whole step from D, skipping D♯ |
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| F♯ | M indicates a whole step from E, skipping F |
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| G | m indicates a half step from F♯, skipping nothing |

‎exercises/practice/scale-generator/.meta/config.json

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{
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"authors": [
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"pfertyk"
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],
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"files": {
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"solution": [
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"scale_generator.gd"
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],
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"test": [
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"scale_generator_test.gd"
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],
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"example": [
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".meta/example.gd"
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]
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},
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"blurb": "Generate musical scales, given a starting note and a set of intervals."
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}

‎exercises/practice/scale-generator/.meta/example.gd

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const ASCENDING_INTERVALS = ['m', 'M', 'A']
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const CHROMATIC_SCALE = ['A', 'A#', 'B', 'C', 'C#', 'D', 'D#', 'E', 'F', 'F#', 'G', 'G#']
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const FLAT_CHROMATIC_SCALE = ['A', 'Bb', 'B', 'C', 'Db', 'D', 'Eb', 'E', 'F', 'Gb', 'G', 'Ab']
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const FLAT_KEYS = ['F', 'Bb', 'Eb', 'Ab', 'Db', 'Gb', 'd', 'g', 'c', 'f', 'bb', 'eb']
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@export var tonic : String
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func chromatic():
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return _reorder_chromatic_scale()
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func interval(intervals):
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var last_index = 0
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var pitches = []
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var scale = _reorder_chromatic_scale()
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for interval in intervals:
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pitches.append(scale[last_index])
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last_index += ASCENDING_INTERVALS.find(interval) + 1
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pitches.append(tonic.capitalize())
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return pitches
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func _reorder_chromatic_scale():
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var chromatic_scale = (FLAT_CHROMATIC_SCALE if tonic in FLAT_KEYS else CHROMATIC_SCALE)
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var index = chromatic_scale.find(tonic.capitalize())
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return chromatic_scale.slice(index) + chromatic_scale.slice(0, index)

‎exercises/practice/scale-generator/.meta/tests.toml

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# This is an auto-generated file.
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#
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# Regenerating this file via `configlet sync` will:
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# - Recreate every `description` key/value pair
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# - Recreate every `reimplements` key/value pair, where they exist in problem-specifications
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# - Remove any `include = true` key/value pair (an omitted `include` key implies inclusion)
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# - Preserve any other key/value pair
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#
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# As user-added comments (using the # character) will be removed when this file
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# is regenerated, comments can be added via a `comment` key.
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[10ea7b14-8a49-40be-ac55-7c62b55f9b47]
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description = "Chromatic scales -> Chromatic scale with sharps"
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[af8381de-9a72-4efd-823a-48374dbfe76f]
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description = "Chromatic scales -> Chromatic scale with flats"
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[7195998a-7be7-40c9-8877-a1d7949e061b]
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description = "Scales with specified intervals -> Simple major scale"
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reimplements = "6f5b1410-1dd7-4c6c-b410-6b7e986f6f1e"
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[fe853b97-1878-4090-b218-4029246abb91]
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description = "Scales with specified intervals -> Major scale with sharps"
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reimplements = "13a92f89-a83e-40b5-b9d4-01136931ba02"
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[d60cb414-cc02-4fcb-ad7a-fc7ef0a9eead]
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description = "Scales with specified intervals -> Major scale with flats"
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reimplements = "aa3320f6-a761-49a1-bcf6-978e0c81080a"
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[77dab9b3-1bbc-4f9a-afd8-06da693bcc67]
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description = "Scales with specified intervals -> Minor scale with sharps"
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reimplements = "63daeb2f-c3f9-4c45-92be-5bf97f61ff94"
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[5fa1728f-5b66-4b43-9b7c-84359b7069d4]
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description = "Scales with specified intervals -> Minor scale with flats"
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reimplements = "616594d0-9c48-4301-949e-af1d4fad16fd"
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[f3f1c353-8f7b-4a85-a5b5-ae06c2645823]
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description = "Scales with specified intervals -> Dorian mode"
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reimplements = "390bd12c-5ac7-4ec7-bdde-4e58d5c78b0a"
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[5fe14e5a-3ddc-4202-a158-2c1158beb5d0]
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description = "Scales with specified intervals -> Mixolydian mode"
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reimplements = "846d0862-0f3e-4f3b-8a2d-9cc74f017848"
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[e6307799-b7f6-43fc-a6d8-a4834d6e2bdb]
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description = "Scales with specified intervals -> Lydian mode"
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reimplements = "7d49a8bb-b5f7-46ad-a207-83bd5032291a"
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[7c4a95cd-ecf4-448d-99bc-dbbca51856e0]
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description = "Scales with specified intervals -> Phrygian mode"
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reimplements = "a4e4dac5-1891-4160-a19f-bb06d653d4d0"
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[f476f9c9-5a13-473d-bb6c-f884cf8fd9f2]
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description = "Scales with specified intervals -> Locrian mode"
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reimplements = "ef3650af-90f8-4ad9-9ef6-fdbeae07dcaa"
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[87fdbcca-d3dd-46d5-9c56-ec79e25b19f4]
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description = "Scales with specified intervals -> Harmonic minor"
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reimplements = "70517400-12b7-4530-b861-fa940ae69ee8"
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[b28ecc18-88db-4fd5-a973-cfe6361e2b24]
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description = "Scales with specified intervals -> Octatonic"
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reimplements = "37114c0b-c54d-45da-9f4b-3848201470b0"
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[a1c7d333-6fb3-4f3b-9178-8a0cbe043134]
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description = "Scales with specified intervals -> Hexatonic"
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reimplements = "496466e7-aa45-4bbd-a64d-f41030feed9c"
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[9acfd139-0781-4926-8273-66a478c3b287]
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description = "Scales with specified intervals -> Pentatonic"
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reimplements = "bee5d9ec-e226-47b6-b62b-847a9241f3cc"
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[31c933ca-2251-4a5b-92dd-9d5831bc84ad]
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description = "Scales with specified intervals -> Enigmatic"
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reimplements = "dbee06a6-7535-4ab7-98e8-d8a36c8402d1"
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[6f5b1410-1dd7-4c6c-b410-6b7e986f6f1e]
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description = "Scales with specified intervals -> Simple major scale"
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include = false
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[13a92f89-a83e-40b5-b9d4-01136931ba02]
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description = "Scales with specified intervals -> Major scale with sharps"
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include = false
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[aa3320f6-a761-49a1-bcf6-978e0c81080a]
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description = "Scales with specified intervals -> Major scale with flats"
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include = false
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[63daeb2f-c3f9-4c45-92be-5bf97f61ff94]
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description = "Scales with specified intervals -> Minor scale with sharps"
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include = false
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[616594d0-9c48-4301-949e-af1d4fad16fd]
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description = "Scales with specified intervals -> Minor scale with flats"
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include = false
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[390bd12c-5ac7-4ec7-bdde-4e58d5c78b0a]
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description = "Scales with specified intervals -> Dorian mode"
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include = false
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[846d0862-0f3e-4f3b-8a2d-9cc74f017848]
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description = "Scales with specified intervals -> Mixolydian mode"
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include = false
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[7d49a8bb-b5f7-46ad-a207-83bd5032291a]
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description = "Scales with specified intervals -> Lydian mode"
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include = false
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[a4e4dac5-1891-4160-a19f-bb06d653d4d0]
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description = "Scales with specified intervals -> Phrygian mode"
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include = false
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[ef3650af-90f8-4ad9-9ef6-fdbeae07dcaa]
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description = "Scales with specified intervals -> Locrian mode"
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include = false
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[70517400-12b7-4530-b861-fa940ae69ee8]
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description = "Scales with specified intervals -> Harmonic minor"
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include = false
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[37114c0b-c54d-45da-9f4b-3848201470b0]
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description = "Scales with specified intervals -> Octatonic"
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include = false
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[496466e7-aa45-4bbd-a64d-f41030feed9c]
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description = "Scales with specified intervals -> Hexatonic"
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include = false
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[bee5d9ec-e226-47b6-b62b-847a9241f3cc]
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description = "Scales with specified intervals -> Pentatonic"
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include = false
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[dbee06a6-7535-4ab7-98e8-d8a36c8402d1]
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description = "Scales with specified intervals -> Enigmatic"
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include = false

‎exercises/practice/scale-generator/scale_generator.gd

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@export var tonic : String
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func chromatic(self):
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pass
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func interval(self, intervals):
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pass

‎exercises/practice/scale-generator/scale_generator_test.gd

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# Test chromatic scales
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func test_chromatic_scale_with_sharps(scale):
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scale.tonic = "C"
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var expected = ["C", "C#", "D", "D#", "E", "F", "F#", "G", "G#", "A", "A#", "B"]
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return [scale.chromatic(), expected]
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func test_chromatic_scale_with_flats(scale):
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scale.tonic = "F"
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var expected = ["F", "Gb", "G", "Ab", "A", "Bb", "B", "C", "Db", "D", "Eb", "E"]
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return [scale.chromatic(), expected]
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# Test scales with specified intervals
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func test_simple_major_scale(scale):
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scale.tonic = "C"
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var expected = ["C", "D", "E", "F", "G", "A", "B", "C"]
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return [scale.interval("MMmMMMm"), expected]
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func test_major_scale_with_sharps(scale):
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scale.tonic = "G"
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var expected = ["G", "A", "B", "C", "D", "E", "F#", "G"]
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return [scale.interval("MMmMMMm"), expected]
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func test_major_scale_with_flats(scale):
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scale.tonic = "F"
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var expected = ["F", "G", "A", "Bb", "C", "D", "E", "F"]
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return [scale.interval("MMmMMMm"), expected]
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func test_minor_scale_with_sharps(scale):
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scale.tonic = "f#"
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var expected = ["F#", "G#", "A", "B", "C#", "D", "E", "F#"]
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return [scale.interval("MmMMmMM"), expected]
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func test_minor_scale_with_flats(scale):
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scale.tonic = "bb"
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var expected = ["Bb", "C", "Db", "Eb", "F", "Gb", "Ab", "Bb"]
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return [scale.interval("MmMMmMM"), expected]
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func test_dorian_mode(scale):
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scale.tonic = "d"
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var expected = ["D", "E", "F", "G", "A", "B", "C", "D"]
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return [scale.interval("MmMMMmM"), expected]
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func test_mixolydian_mode(scale):
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scale.tonic = "Eb"
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var expected = ["Eb", "F", "G", "Ab", "Bb", "C", "Db", "Eb"]
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return [scale.interval("MMmMMmM"), expected]
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func test_lydian_mode(scale):
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scale.tonic = "a"
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var expected = ["A", "B", "C#", "D#", "E", "F#", "G#", "A"]
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return [scale.interval("MMMmMMm"), expected]
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func test_phrygian_mode(scale):
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scale.tonic = "e"
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var expected = ["E", "F", "G", "A", "B", "C", "D", "E"]
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return [scale.interval("mMMMmMM"), expected]
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func test_locrian_mode(scale):
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scale.tonic = "g"
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var expected = ["G", "Ab", "Bb", "C", "Db", "Eb", "F", "G"]
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return [scale.interval("mMMmMMM"), expected]
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func test_harmonic_minor(scale):
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scale.tonic = "d"
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var expected = ["D", "E", "F", "G", "A", "Bb", "Db", "D"]
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return [scale.interval("MmMMmAm"), expected]
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func test_octatonic(scale):
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scale.tonic = "C"
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var expected = ["C", "D", "D#", "F", "F#", "G#", "A", "B", "C"]
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return [scale.interval("MmMmMmMm"), expected]
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func test_hexatonic(scale):
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scale.tonic = "Db"
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var expected = ["Db", "Eb", "F", "G", "A", "B", "Db"]
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return [scale.interval("MMMMMM"), expected]
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func test_pentatonic(scale):
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scale.tonic = "A"
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var expected = ["A", "B", "C#", "E", "F#", "A"]
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return [scale.interval("MMAMA"), expected]
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func test_enigmatic(scale):
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scale.tonic = "G"
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var expected = ["G", "G#", "B", "C#", "D#", "F", "F#", "G"]
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return [scale.interval("mAMMMmm"), expected]
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