Velato (2009)


Velato is a programming language which uses MIDI files as source code: the pattern of notes determines commands. Velato offers an unusual challenge to programmer-musicians: to compose a musical piece that, in addition to expressing their aims musically, fills the constraints necessary to compile to a working Velato program. Each song has a secret message: the program it determines when compiled as Velato.


Velato on Esolangs.org


A three-part introduction to the language:


Download the compiler


Create Digital Music's coverage of Velato


Velato is currently Windows-only, and requires the .NET Framework 3.5 to run.


This is freeware, do whatever you want with it; just don't sell it.


This download includes the compiler itself, and Stephen Toub's MIDI library, used to read the .mid files.


Intro

Velato is a programming language which uses MIDI files as source code. Commands are determined by the intervals between notes.

Velato commands

All commands in Velato are expressed strictly by the pitch and order of notes. With the exception of variable names (more on this below), only the interval between notes is relevant, rather than the pitch itself.

The range of pitches is the alphabet in which Velato commands are written. This means that time signature, key signature, measures, rests, repeat marks, even note durations, are ignored by the code. If two notes are played as a chord, with no delay between the sounding of the notes, the one which appears first in the MIDI file is interpreted first, as if they had not been played simultaneously.

The commands and expressions themselves are determined by intervals from a command root note, which is the first note of the song. Therefore, a valid Velato program in one key can be translated to any other key, with no effect on the program. To allow versatility in Velato composition, the key can also be changed between any two commands within the song (using the "change command root" command). This allows the programmer to choose a starting pitch that better fits the flow of the song.

Also, additional tracks can be added to the MIDI file, which will be ignored by the compiler. This can allow any Velato program to be accompanied, without affecting the program.

For example: "C A G E D D", in the key of C, prints the variable D to the screen. In the key of G, the same command would be "G E D B A D". The actual definition of the print command are the set of intervals: Root (in the first case C), Major 6th (from root), Perfect 5th. The remaining three notes determine that it's variable D to print to the screen. Note that we did not transpose the final D, which is the name of the variable. For commands and expressions (except variables), octave is ignored, so an A in any octave has the same meaning. Also, notes are determined by pitch, not the actual written note, so G# and Ab are equivalent.

As mentioned above, variables are an exception. They are specific to octave and are not determined by interval; so command root changes do not affect them. This allows the program to have as many variables as there are notes allowed in the MIDI specification. This also makes programs less confusing to follow (having a different pitch for the same variable throughout a song would be confusing).


Commands


The Command Root Note

Expressions

Numbers

Variables

Statements

Functions

Other missing features

The following blog post will list all Velato commands.


Command List

Here is the complete list of commands currently implemented in Velato. For an introduction to the language, see the intro.

List of Commands

All statements start with the command root, followed by one of the following commands. Intervals are from the currant command root note.

command second note third note followed by...
Change Root Note Major 2nd
New root note
Let (assignment) Minor 3rd
Variable as single note, then expression
Declare variable Minor 6th
Variable as single note, then type
Blocks Major 3rd

While
Major 3rd
End While
Perfect 4th
If
Perfect 5th
Else
Major 6th
End If
Major 7th
Special Commands Major 6th

Print to screen
Perfect 5th Expression to print




List of Other Expressions

If an operation is expecting an expression, the list that follows will determine what expression is interpreted. Expressions do not start with the command root note, but all intervals are still determined from it.

Expressions don't differentiate between perfect/diminished, major/minor, so that they can be diatonic to the scale used in the rest of the command. For example, if you're in C, this helps you avoid having a progression like C E C Eb, which could sound random or unmusical, depending on context. The programmer can pick which of the two intervals fits the song better.

expression first note second note third note followed by...
value 3rd (maj/min)


variable
2nd
Name of varaible (since note)
pos. (+) int
5th
Single note for each digit, ending with Perfect 5th to mark end of number
neg. (-) int
3rd
Single note for each digit, ending with Perfect 5th to mark end of number
char
4th
Char as ASCII int: single note for each digit, ending with Perfect 5th to mark end of number
pos. (+) double
6th
Single note for each digit, first Perfect 5th to mark decimal point, second Perfect 5th marking end of number
neg. (-) double
7th
Single note for each digit, first Perfect 5th to mark decimal point, second Perfect 5th marking end of number
conditional 2nd


=
2nd

>
3rd

<
4th

NOT
5th
(also used for NOT < (indicating greater than or equal to) and NOT =
AND
6th

OR
7th

procedural 6th


grouping
6th

(

6th
)

2nd
math operation 5th


simple
5th

+

3rd
-

2nd
*

5th
/

4th
% (mod)

6th
exponential / other
7th

power

2nd
log

3rd


The only interval without a choice is a 4th. There is no augmented 4th, a tritone is always interpreted as a diminished 5th.

Each number of half-steps is interpreted as a unique interval -- so that there are no enharmonic intervals that may lead to ambigous commands. If an expression requires a 4th, only the Perfect 4th can be used, not an augmented 4th (tritone), which is considered a Diminished 5th in Velato. If a 3rd is required, either the Minor 3rd or Major 3rd can be used.

This is the interval list used by Velato:

2nd Minor 2nd 1 half-step
2nd Major 2nd 2 half-steps
3rd Minor 3rd 3 half-steps
3rd Major 3rd 4 half-steps
4th Perfect 4th 5 half-steps
5th Diminished 5th 6 half-steps
5th Perfect 5th 7 half-steps
6th Minor 6th 8 half-steps
6th Major 6th 9 half-steps
7th Minor 7th 10 half-steps
7th Major 7th 11 half-steps



Types:

When a type needs to indicated (such as in a variable declaration), this table shows how they are indicated:

type note
int 2nd
char 3rd
double 4th




Numbers:

Individual digits in a number are determined by half-steps from the command root, excluding the Perfect 5th.

In C, these are the numbers tied to each note:

c# d d# e f f# g g# a a# b
0 1 2 3 4 5 - 6 7 8 9



Characters:

All characters are entered by their ASCII int. You can find a table of ASCII values here.

That's pretty much it. There are a few commands/expressions not yet implemented in Velato -- when they become available, I'll add them to this post.

The next post will be a walk-through of how to write programs in Velato.


The GUIDO Notation System is a very intuitive notation for music, so I'll use it for the coding examples. To convert GUIDO scripts to MIDI files, there's the gmn2midi converter. There are plenty of other notation systems (such as LilyPond) which work equally well.

In GUIDO, notes are represented in the format G0/2, where G is the note, 0 is the octave (equivalent to octave 5 in MIDI), and /2 represents a half-note. If the octave is not provided for a note, it uses the previous note's octave -- same for note durations. Rests are underscores. Comments are Pascal-style (* *) and can be used to track commands within the .gmn file.

The actual program

Okay, let's start with printing the 'H' character to the screen. The Velato command to print a character is Major 6th, Major 5th. If we're writing in C, this is the progression C A G (we always have to start commands with the command root note, which, in this case, is C, as we're starting the program with it).

Looking at the expression list in this post, The expression for a char value is 3rd, 4th. The first 3rd could be major or minor, but since we've used E already, we'll use that, as opposed to E& (which is the GUIDO representation of E-flat).

This we follow with the ASCII value of 'H'. This happens to be 72 (there's a list here), which we represent as "a d#" (we get this from the number of half-steps up from the command root, starting up a half-step, and excluding the Perfect 5th -- it's probably easier to just write it out once and refer to it, like the chart in the last post, here). Unfortunately, we ended up using a d# (equivalent to e&) after all. We can make this more palatable by making it part of a chord, either by combining it with the notes ahead or behind it, or with notes in additional tracks which are not part of the program.

We end the integer with a Perfect 5th, which is G. This gives us the complete command:

[ c a g e f a d# g ]



Click to hear actual midi file

After creating a .mid file with gmn2midi, we use Vlt to compile, and see this abstract syntax tree. This helps us verify that we used the correct notes, and didn't end up with some command we didn't intend:

Program

DeclareFunction

PrintToScreen

CharConstant


Now, let's make it sound a bit better.

We can turn this into several chords: a C6 and an F7. Since we're at the end of a command, we can add a C after (that's our command root), which will be interpreted as No-ops. In Guido, we use curly brackets to indicate notes played together -- the notes of the chord are seperated by comma.

This would give us this:

[ {c-1/4, a1, g0, e } { f/4, a, d#1} _/8 
{ g0/4., c1 } ]



midi file

This is an equivalent command (both print the letter 'H'), but the second is a bit more musical. In addition to creating chords, I've also spread the notes into several octaves and altered the rhythma bit.

Next, let's change the command root note to an F. We do this with a Major 2nd interval, followed by the new root note. In this case:

c d f



Now we write the next command (to print 'e'), starting from F instead of C. The first part of the command is the same, only transposed:

f d c a b&



In ASCII, 'e' is 101, which is g f# g -- we end with a Perfect 5th to indicate the end of an integer, so that's a "c" again. The whole command is:

f d c a b& g f# g c



We can combine this with the previous command ('c d f') and make it a bit more musical:

c0/16 d1 f {f-1/8, d1, c0, a} 
{b&1/4, g-1, f#0} _/8 { g0/4., c1}



entire song so far

It's not going to win us any awards for composition yet, but at least it sounds intentional, instead of a bunch of random notes.

Let's change the command root to B& for a bit of a change, and print the next character, the first 'l'.

The two commands are:

f g b& (* change of command root *)

b& g f d e& c b a& f (* print 'l' *)



Or, once we change the rhythm and octaves:

f0/16 g1 b& (* change of command root *)

{b&-1/8, g1, f0, d} {e&1/4, c0, b0} a&1/8
{f/4, b&} b&0 (* print 'l' *)


entire song so far

The rest of the notes are selected using the same technique. We're not going to win any Grammys with our final program, but it's at least somewhat musical (in a free-form jazz sorta way) instead of random notes. With more time and effort, the song could be further composed into something more pleasing. I'll post any further re-workings of the song here.

Complete "Hello, World" program midi file

GUIDO source for complete program

Here's the program as sheet music. Keep in mind that this set of notes is *not* the actual program; if a MIDI file is created from this progression of notes, the concurrent notes might be interpreted in a different order in the file, and create an invalid program.