FunC literals

The official smart contract language of TON Blockchain is Tolk. FunC is now a legacy language, with its compiler no longer maintained.

FunC pages will be moved down in the sidebar in mid-April 2026. Here is the preview of a possible future placement, right between "Blockchain foundations" and "Contribute" sections:

Learn how to migrate from FunC to Tolk.

Number literals

FunC supports decimal and hexadecimal integer literals, including those with leading zeros:

• Examples of valid integer literals: 0, 123, -17, 00987, and -0.
  
• Examples of valid hexadecimal literals: 0xef, 0xEF, 0x0, -0xfFAb, 0x0001, and -0x0.

Identifiers

FunC allows a broad range of identifiers for functions and variable names. Any single-line string that meets the following conditions qualifies as a valid identifier:

• It does not contain special symbols: ;, ,, (, ), [, ], spaces including tabs, ~, and ..
• It does not start as a comment or a string literal (i.e., with " at the beginning).
• It is not a number literal.
• It is not an underscore _.
• It is not a reserved keyword.
• It is not the name of a built-in.

Additionally, function names in function definitions can start with . or ~.

Examples of valid identifiers:

• query, query', query''
• elem0, elem1, elem2
• CHECK
• _internal_value
• message_found?
• get_pubkeys&signatures
• dict::udict_set_builder
• fatal!

Examples of less common, but still valid identifiers:

• 123validname
• 2+2=2*2
• -alsovalidname
• 0xefefefhahaha
• {hehehe}
• pa{--}in"`aaa`"

Examples of valid function names:

• fun_a
• ~fun_a?
• ._how123

Examples of invalid identifiers:

• take(first)Entry - contains parentheses ( and )
• "not_a_string - starts with a ", like a string literal
• msg.sender - includes a .
• send_message,then_terminate - contains a ,
• _ - just an underscore, which is not valid on its own
• pa;;in"`aaa`" - contains ;
• {-aaa-} - it is a comment
• aa(bb - contains an opening parenthesis
• 123 - a number literal
• _+_ - it is a reserved builtin name

Special identifiers in backticks:

FunC allows identifiers enclosed in backticks `.

These identifiers can contain any characters except:

• Newline characters \n
• Backticks ` themselves, except the opening and closing ones.

Examples of valid backtick identifiers:

• `I'm a variable identifier too`
• `any symbols ; ~ () are allowed here...`

Constants

FunC allows defining compile-time constants that are substituted and pre-computed during compilation.

Syntax:

const optional-type identifier = value-or-expression;

• optional-type (e.g., int or slice) is optional but improves readability and ensures type correctness.
• value-or-expressioncan be a literal or an expression involving literals and previously defined constants.

Multiple constants can be defined in the same const declaration by separating them with ,.

Example usage:

const int101 = 101;                      ;; Numeric constant
const str1 = "const1", str2 = "aabbcc"s; ;; Multiple string constants separated with ,
const int int240 = (int101 * 10) << 3;   ;; Constant computed from an expression
const slice str2r = str2;                ;; Constant referencing another constant

Compile-time built-ins

FunC has a special syntax for compile-time operations that compute slices and integer hashes out of ASCII strings. These compile-time operations are invoked by enclosing the ASCII string in double quotes ", followed by a suffix representing the compile-time operation to apply on the string, like:

"this is a string"u

where the suffix u represents the compile-time operation to invoke on the ASCII string.

These built-ins are evaluated during compilation time, which means that the FunC compiler replaces the built-in call anywhere it occurs with the result of the call. In particular, it is possible to use these compile-time built-ins while declaring constants:

const c = "some string"s;

We now describe the possible string suffixes.

String without suffix

If no suffix is provided, the compiler computes a slice from the ASCII string, such that the contents of the slice is the binary code of the ASCII string.

const c = "hello";     ;; c has the slice x{68656c6c6f}, where 68656c6c6f
                       ;; is the slice contents in hexadecimal, representing
                       ;; the ASCII code of the string.

String with suffix s

Suffix s interprets the string as an hexadecimal number and produces a slice having the binary representation of the hexadecimal number. If the string is not an hexadecimal number, the compiler signals an error.

const c = "abcdef"s;   ;; c has the slice x{abcdef}, where abcdef is the
                       ;; slice contents in hexadecimal.
                       ;; Note that abcdef is a valid hexadecimal number.

String with suffix a

Suffix a interprets the string as an address and creates a slice containing a MsgAddressInt structure from the address.

;; c has slice x{9FE6666666666666666666666666666666666666666666666666666666666666667_}
;; The slice contents represent the MsgAddressInt structure:
;; addr_std$10 anycast:none$0 workchain_id:int8=0xFF address:bits256=0x33...33
const c = "Ef8zMzMzMzMzMzMzMzMzMzMzMzMzMzMzMzMzMzMzMzMzM0vF"a;

String with suffix u

Suffix u produces the decimal representation of the binary code of the ASCII string.

const c = "NstK"u;     ;; c has the integer 1316189259
                       ;; which is the decimal representation of the
                       ;; ASCII code of the string

String with suffix h

Suffix h generates an integer from the first 32 bits of the string's SHA-256 hash.

const c = "transfer(slice, int)"h;  ;; c has the integer 2053302440

String with suffix H

Suffix H generates an integer from the full 256-bit SHA-256 hash of the string.

;; c has the integer
;; 55356924298749527416066000120313684523410504308849542670649639903159354505593
const c = "transfer(slice, int)"H

String with suffix c

Suffix c generates an integer from the crc32 value of the string.

const c = "transfer(slice, int)"c   ;; c has the integer 2235694568

String with multiple lines

Special characters like \n are not supported in strings, but you can create multi-line strings by writing the text across multiple lines, all surrounded by triple quotes """. The triple quotes syntax also supports the previously described suffixes.

For example:

int a = """
   hash me baby one more time
   .... Oh, baby, baby
"""h;     ;; a has value 876244482