What is this?

NNotepad is a browser-based playground for experimenting with WebNN expressions without boilerplate code. As of mid-2024, WebNN is available as a prototype in Chromium-based browsers, but requires launching the browser with particular flags enabled.

Usage

Type assignments like foo = 1 + 2 or expressions like 2 * foo. The result of the last assignment or expression is shown. Some examples:

1 + 2
# yields 3

a = 123
b = 456
a / b
# yields 0.2697368562221527

A = [[1,7],[2,4]]
B = [[3,3],[5,2]]
matmul(A,B)
# yields [[38,17],[26,14]]

NNotepad translates what you type into script that builds a WebNN graph, evaluates the script, then executes the graph. Click 🔎 to see the generated script.

Expressions can use:

• Operators +, -, *, /, ^, ==, <, <=, >, >=, ! with precedence, and (,) for grouping.
• Function calls like add(), matmul(), sigmoid(), and so on.
• Numbers like -12.34.
• Tensors like [[1,2],[3,4]].
• Dictionaries like {alpha: 2, beta: 3}, arrays like [ A, B ], strings like "float32", and booleans true and false.

Functions and operators are turned into MLGraphBuilder method calls.

Array literals ([...]) and number literals (12.34) are interpreted contextually:

• In assignments, they are intepreted as tensor/scalar constant MLOperands, e.g. alpha = 12.34 or T = [1,2,3,4].
• In most function calls, they are interpreted as tensor/scalar constant MLOperands, e.g. neg(123) or neg([1,2,3]).
• In some function calls, they are interpreted as arrays/numbers for some positional parameters, e.g. concat([A,B,C],0). This includes: concat(), expand(), pad(), reshape(), slice(), split().
• In dictionaries, they are interpreted as arrays/numbers, e.g. linear(123, {alpha: 456, beta: 789}) or transpose(T, {permutation: [0,2,1]}). To pass a tensor/scalar constant in a dictionary, use a variable or wrap it in identity() e.g. gemm(A, B, {c:identity([4])}) or gemm(A, B, {c:identity(4)}).

The default data type for scalars and tensors is float32. To specify a different data type, suffix with one of i8, u8, i32, u32, i64, u64, f16, f32, e.g. 123i8 or [1,2,3]u32.

Helpers

In addition to WebNN MLGraphBuilder methods, you can use these helpers:

• load(url, shape, dataType) - fetch a tensor resource. Must be served with appropriate CORS headers. Example: load('https://www.random.org/cgi-bin/randbyte?nbytes=256', [16, 16], 'uint8')
• zeros(shape, dataType) - constant zero-filled tensor of the given shape. Example: zeros([2,2,2,2], 'int8')

Details & Gotchas

• float16 support (and the f16 suffix) is experimental.
• Whitespace including line breaks is ignored.
• Parsing around the "unary minus" operator can be surprising. Wrap expressions e.g. (-a) if you get unexpected errors.
• If output is a constant, it will be wrapped with identity() if your back-end supports it. Otherwise, you must introduce a supported expression.

What ops are supported, and with what data types, depends entirely on your browser's WebNN implementation. Here be dragons!

Parsing & Grammar

Anything after # or // on a line is ignored (outside other tokens)

{} means 0-or-more repetitions
[] means 0-or-1 repetitions
() for grouping
| separates options
'' is literal
// is regex

program = line { line }
line = assigment | expr
assigment = identifier '=' expr

expr = relexpr
relexpr = addexpr { ( '==' | '<' | '<=' | '>' | '>=' ) addexpr }
addexpr = mulexpr { ( '+' | '-' ) mulexpr }
mulexpr = powexpr { ( '*' | '/' ) powexpr }
powexpr = unyexpr { '^' unyexpr }
unyexpr = ( '-' | '!' ) unyexpr
        | finexpr
finexpr = number [ suffix ]
        | array [ suffix ]
        | string
        | boolean
        | dict
        | identifier [ '(' [ expr { ',' expr } ] ')' ]
        | '(' expr ')'

string = /("([^\\\x0A\x0D"]|\\.)*"|'([^\\\x0A\x0D']|\\.)*')/
number = /NaN|Infinity|-Infinity|-?\d+(\.\d+)?([eE]-?\d+)?/
boolean = 'true' | 'false'
identifier = /[A-Za-z]\w*/
suffix = 'u8' | 'u32' | 'i8' | 'i32' | 'u64' | 'i64' | 'f16' | 'f32'

array = '[' [ expr { ',' expr } ] ']'

dict = '{' [ propdef { ',' propdef  } [ ',' ] ] '}'
propdef = ( identifier | string ) ':' expr