Wuffs the Language

The Wuffs project is both a programming language and a standard library written in that programming language (and then e.g. transpiled to C). For more details on the latter, see the Wuffs the Library document. As for Wuffs the Language, it is an imperative C-like memory-safe language that should look roughly familiar to somebody versed in one of C, C++, Go, Java, JavaScript, Rust, etc. The major differentiating features are:

Minor features or restrictions include:

  • Nullable and non-nullable pointers, spelled nptr T and ptr T.
  • Integrated I/O.
  • Iterate loops.
  • Public vs private API is marked with the pub and pri keywords. Visibility boundaries are at the package level, unlike C++ or Java's type level.
  • No variable shadowing. All local variables must be declared before any other statements in a function body.
  • Like Go, semi-colons can be omitted. Similarly, the () parentheses around an if or while condition are optional, but the {} curly braces are mandatory. There is no ‘dangling else’ ambiguity.
  • Labeled jumps look like break.loopname and continue.loopname, for a matching while.loopname. The while.loopname's closing curly brace must be followed by endwhile.loopname.
  • A while true loop‘s block may use double-curly braces: {{ and }}. The formatter will not add an indent to the code inside the block. This is useful when using while true {{ etc; break; etc; break }} to simulate what would be a (forwards) goto in other languages’ straight-line code.

Wuffs code is formatted by the wuffsfmt program.


Types read from left to right: ptr array[100] base.u32 is a non-null pointer to a 100-element array of unsigned 32-bit integers. Types can also be refined.


Structs are a list of fields, enclosed in parentheses: struct foo(x: base.u32, y: base.u32), possibly extended (by a +) with a second list of optionally initialized fields. The struct name, foo, may be followed by a question mark ?, which means that its methods may be coroutines.


All functions are methods (with an implicit this argument). There are no free-standing functions.

Function definitions read from left to right. func foo.bar(x: base.u32, y: base.u32) base.u32 is a function (a method on the foo struct type) that takes two base.u32s and returns a base.u32. Each argument must be named at the call site. It is m = f.bar(x: 10, y: 20), not m = f.bar(10, 20).


There is no operator precedence. A bare a * b + c is an invalid expression. You must explicitly write either (a * b) + c or a * (b + c).

Some binary operators (+, *, &, |, ^, and, or) are also associative: (a + b) + c and a + (b + c) are equivalent, and can be spelled a + b + c.

The logical operators, && and || and ! in C, are spelled and and or and not in Wuffs. Not-equals is spelled <>, as the ! exclamation mark is reserved for impure effects.

Expressions involving the standard arithmetic operators (e.g. *, +), will not compile if overflow is possible. Some of these operators have alternative ‘tilde’ forms (e.g. ~mod*, ~sat+) which provide modular and saturating arithmetic. By definition, these never overflow.

The as operator, e.g. x as T, converts an expression x to the type T.


There is no string type. There are arrays and slices of bytes (base.u8s), but bear in mind that Wuffs code cannot allocate or free memory.

Double-quoted literals like "#bad checksum" are actually statuses, axiom names or a use "std/foo" package name.

Single-quoted literals are actually numerical constants. For example, 'A' and '\t' are equivalent to 0x41 and 0x09. These literals are not restricted to a single ASCII byte or even a single Unicode code point, and can decode to multiple bytes when finished with a be or le endianness suffix. For example, '\x01\x02'be is equivalent to 0x0102. Similarly, '\u0394?'le (which can also be written 'Δ?'le) is equivalent to 0x3F94CE, because the UTF-8 encodings of U+0394 GREEK CAPITAL LETTER DELTA and U+003F QUESTION MARK (the ASCII ?) is (0xCE, 0x94) and (0x3F).

Double-quoted literals cannot contain backslashes, as they'd be an unnecessary complication. Single-quoted literals can contain backslash-escapes, as they are often compared with arbitrary binary data. For example, where other programming languages would check if JPEG data starts with the magic string "\xFF\xD8", Wuffs would check if its opening 2 bytes, read as a little-endian base.u16, is a number that equals '\xFF\xD8'le.

Introductory Example

A simple Wuffs the Language program, unrelated to Wuffs the Library, is discussed in /hello-wuffs-c.