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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.

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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: Additionally, function names in function definitions can start with . or ~.
FunC allows an exception regarding identifiers for local variables. Local variables can use the name of a built-in with a non-symbolic name.
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...`
Identifiers in FunC usually follow these naming conventions:
  • Apostrophe ' at the end: used when a variable is a modified version of its original value.
    • Example: 
      cell dict' = udict_set(dict, 100, 0, v);
      Here, function udict_set updates key 0 with value v in dictionary dict. The updated dictionary name is dict'.
  • Question mark ? at the end: typically used for boolean variables or functions that return a success flag.
    • Example: 
      (slice v, int found?) = udict_get?(dict, 100, 0);
      Here, function udict_get? looks up index 0 in dictionary dict, and returns the associated value v (if found) and a flag found? which indicates whether the index was found in the dictionary.

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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
Numeric constants are replaced during compilation, which means that all optimizations and pre-computations apply efficiently.

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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.

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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.

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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.

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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;

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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

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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

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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

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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

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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