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Parse CMaj7, CmMaj7 and C°7 as the sevenths they name #332

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Merged
matt-edmondson merged 1 commit into from
Sep 29, 2026
Merged

Parse CMaj7, CmMaj7 and C°7 as the sevenths they name #332

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9 changes: 7 additions & 2 deletions Semantics.Music/Chord.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -367,7 +367,10 @@ private static bool IsMinor(string body) =>
private static SeventhType DetermineSeventh(string body, ChordQuality quality)
{
bool hasSeven = body.Contains('7');
bool hasMaj7 = body.Contains("maj", StringComparison.Ordinal) || body.Contains("M7", StringComparison.Ordinal) || body.Contains('Δ');
bool hasMaj7 = body.Contains("maj", StringComparison.Ordinal)
|| body.Contains("Maj", StringComparison.Ordinal)
|| body.Contains("M7", StringComparison.Ordinal)
|| body.Contains('Δ');

// The major seventh is tested first because one body can carry both spellings: "dimmaj7"
// is the diminished-major seventh, a chord distinct from "dim7", and it is what the
Expand All @@ -379,7 +382,9 @@ private static SeventhType DetermineSeventh(string body, ChordQuality quality)
return SeventhType.Major;
}

if (quality == ChordQuality.Diminished && body.Contains("dim", StringComparison.Ordinal) && hasSeven)
// '°' is accepted here as it is for the triad, so "C°7" is the diminished seventh rather than
// falling through to a dominant seventh on a diminished triad, which is the half-diminished chord.
if (quality == ChordQuality.Diminished && (body.Contains("dim", StringComparison.Ordinal) || body.Contains('°')) && hasSeven)
{
return SeventhType.Diminished;
}
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14 changes: 14 additions & 0 deletions Semantics.Test/Music/ChordTests.cs
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Expand Up @@ -69,6 +69,20 @@ public void ChordTones_DiminishedMajorSeventh_HasTheMajorSeventhNotTheDoubleFlat
Assert.AreSequenceEqual([0, 3, 6, 11], actual, "Cdimmaj7 should be a diminished triad with a major seventh.");
}

[TestMethod]
[DataRow("CmMaj7", ChordQuality.Minor, SeventhType.Major, new[] { 0, 3, 7, 11 })]
[DataRow("CMaj7", ChordQuality.Major, SeventhType.Major, new[] { 0, 4, 7, 11 })]
[DataRow("C°7", ChordQuality.Diminished, SeventhType.Diminished, new[] { 0, 3, 6, 9 })]
public void Parse_AlternativeSeventhSpellings_GiveTheSeventhTheyName(string symbol, ChordQuality quality, SeventhType seventh, int[] tones)
{
// A round-trip alone cannot catch these: the misparsed chord formats and re-parses
// consistently, so the seventh type and the pitches have to be asserted directly.
Chord c = Chord.Parse(symbol);
Assert.AreEqual(quality, c.Quality, symbol);
Assert.AreEqual(seventh, c.Seventh, symbol);
Assert.AreSequenceEqual(tones, [.. c.ChordTones()], symbol);
}

[TestMethod]
public void Parse_HalfDiminished_IsDiminishedTriadWithDominantSeventh()
{
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