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Literals and identifiers

Number literals​

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

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

String literals​

In FunC, strings are enclosed in double quotes ", like "this is a string".
Special characters like \n and multi-line strings are not supported.
Optionally, a type can be specified after a string literal, such as "string"u.

FunC supports the following string types:

  • without type – Used for asm function definitions and defining a slice constant from an ASCII string.
  • s— Defines a raw slice constant using its contents (hex-encoded and optionally bit-padded).
  • a— Creates a slice constant containing a MsgAddressInt structure from a given address.
  • u— Converts an ASCII string into an integer constant, representing its hex values.
  • h— Generates an integer constant from the first 32 bits of the string’s SHA-256 hash.
  • H— Generates an integer constant from the full 256-bit SHA-256 hash of the string.
  • c— Generates an integer constant from the crc32 value of the string.

Examples The following string literals produce these corresponding constants:

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

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. Exception: if it starts with a backtick `, it must also end with a backtick and cannot contain any additional backticks inside.

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
  • _+_ (the standard addition operator for (int, int) -> int in prefix notation, although it is already defined).
  • fatal!

Naming conventions:

  • Apostrophe ' at the end: used when a variable is a modified version of its original value.

    • Example: almost all modifying built-in primitives for hashmap manipulation (except those with the prefix ~) return a new version of the hashmap, often with extra data. The updated version is typically named with the same identifier, adding a ' suffix.

  • Question mark (?) at the end: typically used for boolean variables or functions that return a success flag.

    • Example: udict_get? from stdlib.fc, which checks if a value exists.

Invalid identifiers:

  • take(first)Entry - contains parentheses ()
  • "not_a_string - starts with a " like a string literal
  • msg.sender - includes a . which is not allowed
  • send_message,then_terminate - contains a , which is not allowed
  • _ - just an underscore, which is not valid on its own

Less common but valid identifiers:

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

More invalid identifiers:

  • pa;;in"`aaa`" - contains ;, which is prohibited
  • {-aaa-} - contains {} incorrectly
  • aa(bb - contains an opening parenthesis without closing it
  • 123 - a number literal, not an identifier

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-quoted identifiers:

  • I'm a variable 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 a pre-computable expression involving literals and constants.

Example usage:

const int101 = 101;                 // Numeric constant
const str1 = "const1", str2 = "aabbcc"s; // String constants
const int int240 = ((int1 + int2) * 10) << 3; // Computed constant
const slice str2r = str2;           // Constant referencing another constant

Since numeric constants are replaced during compilation, all optimizations and pre-computations apply efficiently—unlike the older approach using inline PUSHINT assembly.

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