Grammar Definition

This page is about the definition of mimium grammer.

This page is about the rule of mimium grammer.

Comment out

As in C++ and JavaScript, anything to the right of // in a line is treated as a comment. You can also comment out multiple lines at once by enclosing them as /* */.

Variable declaration and assignment

In mimium, when a value is assigned with the = operator, a new variable is created if the variable with the specified name does not exist yet. There is no need to use keywords such as ``let’’ when declaring variables.

``rust mynumber = 1000 The variables are all modifiable (mutable).

All variables are mutable. All variables are mutable, i.e., you can assign new values to variables that have already been declared.

mynumber = 1000 // variable is declared, and 1000 is assigned
mynumber = 2000 // 2000 is newly assigned to mynumber


Type is a concept to distinguish between variables and other data, such as numbers and strings, depending on their purpose. mimium is a statically typed language, which means that all types are determined at compile time (before the actual sound is made).

Statically typed languages generally have an advantage in terms of execution speed over languages that check types during execution. On the other hand, there is a disadvantage of manual type specification, which tends to lead to long descriptions. mimium has a feature called Type Inference, which allows you to omit type annotations if the type can be automatically determined from the context, thus keeping your code concise.

There are two types: primitive types, which are the smallest unit that cannot be further decomposed, and aggregate types, which are made by combining multiple types.

Explicit annotation of types is possible at the time of variable declaration and function declaration. In the parameters of variables and functions, the type can be specified by writing the name of the type followed by a : (colon).

myvar:float = 100

Assigning to a different type will result in a compile-time error, as shown below.

myvar:string = 100

In function type declarations, the return value can be specified by following the parameter parentheses with a -> between them.

fn add(x:float,y:float)->float{
  return x + y
In the case of this add function, we can predict that x and y are floats from the context [^binaryop], so we can omit it as follows.

fn add(x,y){
  return x+y

Primitive types

The only primitive types in mimium are float, string and void.

The only numeric type in mimium is float (internally a 64bit float). Integers can be used with the round, ceil, and floor functions.

Values of type string can be generated from double-quoted string literals, such as "hoge". Currently, it does not support string cutting or merging, and its usage is basically the same as

  1. pass it to the printstr function for debugging purposes. 2.

  2. pass it to the loadwav function to load an audio file. 3. pass it to include to include it.

  3. pass it to include to load other source files.

  4. pass to include to load other source files.

The void type has no value and is used to indicate that there is no return value for the function.

Composite types


An array is a type that can store multiple values of the same type in succession. It can be generated by comma-separated values enclosed in [] (angle brackets).

myarr = [1,2,3,4,5,6,7,8,9,10]

You can retrieve the value of an array type by specifying a zero-based index with angle brackets, such as myarr[0].

arr_content = myarr[0] //arr_content should be 1

You can also rewrite the contents of the array by using angle brackets on the left side value as well.

myarr[4] = 20 //myarr becomes [1,2,3,4,20,6,7,8,9,10].

**The size of the array is fixed. The size of the array is fixed, so you can’t add values to the back of the array. There is no bounds check, so out-of-range access will cause a crash. ** The size of the array is fixed.

Automatic interpolation

Indexes are automatically linearly interpolated when accessed with decimal values.

arr_content = myarr[1.5] //should be 2.5

There is no automatic rounding to integers, so if you want to avoid interpolation, you need to round the indices using the round function or something similar.


A tuple is a value that combines different types into one. They can be generated by enclosing variables in () (round brackets) and inserting comma-separated variables. Tuples are also similar to arrays, but each element can have a different type.

mytup = (100,200,300)

You can retrieve the value of a tuple by placing a comma-separated variable at the left-hand side value. There is no need to separate them with parentheses in this case.

one,two,three = mytup

Tuples are typically used in mimium to group together channels of audio signals such as stereo and multi-channel in signal processing.

Type Alias

Because type annotation for tuple can be redundant, it can be shorten using type alias semantics.

type FilterCoeffs = (float,float,float,float,float)

Struct(Record Type)

Struct has similar functionality to Tuple type but it can have field names for each type. Struct type cannot be anonymous type. Thus user needs to declare a type alias before initializing value and construct a variable with TypeName{val1,val2...}. The values can be extracted by dot operator like expr.field.

type MyBigStruct = {"field1":float,"field2":FilterCoeffs,"field3":string}

mystr = MyBigStruct{100,(0.0,1.0,1.2,0.8,0.4),"test"}



A function is a collection of reusable procedures that take multiple values and return a new value.

As an example, consider the add function, which just adds two values together and returns them.

To store it as a variable with an explicit type in mimium, write the following

fn add(x,y){
  return x+y

In mimium, functions can be treated as first-class values. This means that you can assign a function to a variable or take it as a parameter of a function.

For example, the type annotation of the previous add function is (float,float)->float. To assign the previous add function to a variable, you can write the following If you want to assign the function as a function parameter, see the section on higher-order functions.

my_function:(float,float)->float = add

Anonymous functions (lambda expressions)

The previous function declaration is actually an alias to the syntax for storing anonymous functions in variables, as shown below.

add = |x:float,y:float|->float{return x+y} 

It is also possible to call such a function directly without assigning it to a variable.

println(|x,y|{return x + y}(1,2)) //print "3"

Also, as will be explained in the block syntax section, the last line of the block can be substituted for return by simply placing an expression in place of return. In other words, the add function, combined with type inference, can be omitted until the following example.

add = |x,y|{x+y}

Pipe (|>) operators

In mimium, you can use the pipe operator |> to rewrite nested function calls like a(b(c(d))) as d |> c |> b |> a.

Looping by recursion

Named functions can also call themselves.

The fact function to compute the factorial can be defined as follows

fn fact(input:float){
    return 1
    return input * fact(input-1)

Use recursive functions with care, as they can cause infinite loops.


In a function, you can use a special keyword called self. self is a variable that can refer to the last value returned by a function. For example, the following function will return a value that increases by increment each time it is called.

fn counter(increment){
  return self+increment

Self is basically only available for functions that originate from the dsp function. self is initialized to 0 when the audio engine is started, and a separate value is created and managed for each calling context. For example, in the following example, the counter function is given a different increment for each of its functions, which internally allocates two pieces of memory for self, with lch increasing by 0.01 samples every time it crosses 1 and resetting to 0, and rch increasing by 0.05 samples every time it crosses 1.

fn dsp()->(float,float){
  lch = counter(0.01)%1
  rch = counter(0.05)%1
  return (lch,rch)

Scope of variables

mimium is a lexical-scoped language, which means that it is possible to refer to variables defined outside of a function.


Expressions, statements, and blocks

A collection of statements enclosed in curly braces {} used in a function, etc. is a unit called a block. A statement almost always consists of a syntax for assigning expressions, such as a = b. expression is a unit consisting of numbers like 1000, variable symbols like mynumber, arithmetic expressions like 1+2*3, and function calls with return values like add(x,y).

Block is actually one of the expressions. You can put multiple statements in a block, and the last line can use return to specify the value to be returned. The return keyword in the last line can also be omitted and just putting expression is allowed.

For example, the following syntax is grammatically correct. (*As of v0.3.0, this syntax is implemented incorrectly and does not work. *)

//mynumber should be 6
mynumber = {
  x = 2
  y = 4
  return x+y


Conditional in mimium has the syntax if (condition) then_expression else else_expression. condition, then_expression, and else_expression are all expressions. If the value of condition is greater than zero, the then_expression part is evaluated, otherwise the else_expression is evaluated.

If the then/else part is expressed as a block, it can be written in a C-like way as follows.

fn fact(input:float){
    return 1
    return input * fact(input-1)

On the other hand, the if statement itself can be treated as an expression, so the same syntax can be rewritten as follows. Note that the parentheses in the conditional part cannot be omitted.

fn fact(input:float){
  return if (input>0) 1 else input * fact(input-1)

Deferred execution with @ operator

You can defer the execution of a function by following the function call with @ followed by a value of numeric type. The unit of time is samples.

For example, the following example writes 100 and 200 to the standard output at the 0th and 48000th samples after starting the audio driver.


Currently, the @ operator can only be used for functions of type void (which have no return value).

By delaying the execution of a recursive function with @, it is also possible to repeat certain operations at regular intervals. For example, the following example will increment the number from 0 to 1 at 48000 sample intervals and write it to the standard output.

fn loopprint(input)->void{


The syntax include("path/to/file.mmm") allows you to include other files in the file.

The file path can be an absolute path or a path relative to the file. Currently, there is no namespace division, and the include statement is purely replaced by the text of the file (but once a file is loaded, it will not be loaded more than once).

Syntax definition by BNF, operator precedence, etc.