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Literals and Identifiers

Number literals

FunC allows decimal and hexadecimal integer literals (leading zeros are allowed).

For example, 0, 123, -17, 00987, 0xef, 0xEF, 0x0, -0xfFAb, 0x0001, -0, -0x0 are valid number literals.

String literals

Strings in FunC are quoted in double quotes " like "this is a string". Special symbols like \n and multi-line strings are not supported. Optionally, string literals may specify a type after them, such as "string"u.

The following string types are supported:

  • without type—used for asm function definitions and to define a slice const by ASCII string
  • s—defines a raw slice const by its contents (hex-encoded and optionally bit-padded)
  • a—creates a slice const containing MsgAddressInt structure from a specified address
  • u—creates an int const that corresponds to the hex values of the provided ASCII string
  • h—creates an int const that is the first 32 bits of the SHA256 hash of the string
  • H—creates an int const that is all 256 bits of the SHA256 hash of the string
  • c—creates an int const that is crc32 value of the string

For example, the following values result in the corresponding consts:

  • "string" becomes x{737472696e67} slice const
  • "abcdef"s becomes x{abcdef} slice const
  • "Ef8zMzMzMzMzMzMzMzMzMzMzMzMzMzMzMzMzMzMzMzMzM0vF"a becomes x{9FE6666666666666666666666666666666666666666666666666666666666666667_} slice const (addr_std$10 anycast:none$0 workchain_id:int8=0xFF address:bits256=0x33...33)
  • "NstK"u becomes 0x4e73744b int const
  • "transfer(slice, int)"h becomes 0x7a62e8a8 int const
  • "transfer(slice, int)"H becomes 0x7a62e8a8ebac41bd6de16c65e7be363bc2d2cbc6a0873778dead4795c13db979 int const
  • "transfer(slice, int)"c becomes 2235694568 int const


FunC allows a really wide class of identifiers (functions and variable names). Namely, any (single-line) string which doesn't contain special symbols ;, ,, (, ), (space or tab), ~ and ., doesn't start as a comment or string literal (with "), isn't a number literal, isn't an underscore _ and isn't a keyword is a valid identifier (with the only exception that if it starts with `, it must end with the same ` and can't contain any other ` except for these two).

Also, function names in function definitions may start with . or ~.

For example, those are valid identifiers:

  • query, query', query''
  • elem0, elem1, elem2
  • _internal_value
  • message_found?
  • get_pubkeys&signatures
  • dict::udict_set_builder
  • _+_ (the standard addition operator of type (int, int) -> int in prefix notation, although it is already defined)
  • fatal!

' at the end of the name of a variable is conventionally used when some modified version of the old value is introduced. For example, almost all modifying built-in primitives for hashmap manipulation (except ones with the prefix ~) take a hashmap and return a new version of the hashmap along with some other data, if necessary. It is convenient to name those values with the same name suffixed by '.

Suffix ? is usually used for boolean variables (TVM doesn't have a built-in type bool; bools are represented by integers: 0 is false and -1 is true) or for functions that return some flag, usually indicating success of the operation (like udict_get? from stdlib.fc).

These are invalid identifiers:

  • take(first)Entry
  • "not_a_string
  • msg.sender
  • send_message,then_terminate
  • _

Some more uncommon examples of valid identifiers:

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

These are also invalid identifiers:

  • pa;;in"`aaa`" (because ; is prohibited)
  • {-aaa-}
  • aa(bb
  • 123 (it's a number)

Also, FunC has a special type of identifiers which is quoted in back quotes `. In the quotes, any symbols are allowed except for \n and the quotes themselves.

For example, `I'm a variable too` is a valid identifier, as well as `any symbols ; ~ () are allowed here...`


FunC allows to define compile-time constants that are substituted and precalculated during compilation.

Constants are defined as const optional-type identifier = value-or-expression;

optional-type can be used to force a specific type of constant and for better readability.

As of now, int and slice types are supported.

value-or-expression can be a literal or a pre-computable expression of literals and constants.

For example, constants can be defined as follows:

  • const int101 = 101; defines int101 constant that is equivalent to the numeric literal 101
  • const str1 = "const1", str2 = "aabbcc"s; defines two constants that are equal to their corresponding strings
  • const int int240 = ((int1 + int2) * 10) << 3; defines int240 constant that equals the result of calculation
  • const slice str2r = str2; defines str2r constant that is equal to the value of str2 constant

Since numeric constants are substituted during compilation, all optimization and pre-computations performed during the compilation are successfully performed (unlike the old method of defining constants via inline asm PUSHINTs).