Built-ins

This section covers extra language constructs that are not part of the core but are still important for functionality. Although they could be implemented in stdlib.fc, keeping them as built-in features allows the FunC optimizer to work more efficiently.

Throwing exceptions

FunC provides several built-in primitives for throwing exceptions:

• Conditional exceptions: throw_if and throw_unless
• Unconditional exception: throw

In throw_if and throw_unless, the first argument (the error code) defines the exception type, while the second argument (the condition) determines whether the exception is thrown. Meanwhile, the throw function takes only one argument—the error code—since it always triggers an exception.

FunC also includes parameterized versions of these primitives:

• Conditional exceptions with parameters: throw_arg_if and throw_arg_unless
• Unconditional exception with a parameter: throw_arg

In these versions, the first argument is an exception parameter of any type, the second defines the error code, and the third argument—used when needed—is a condition that determines whether the exception is thrown.

Booleans

• true is an alias for -1.
• false is an alias for 0.

Dumping a variable

Use the ~dump function to output a variable to the debug log.

Dumping a string

Use the ~strdump function to output a string to the debug log.

Integer operations

• muldiv performs a multiply-then-divide operation. It uses a 513-bit intermediate result to prevent overflow if the final result fits within 257 bits.
• divmod takes two numbers as input and returns the quotient and remainder of their division.

Other primitives

• null? checks if the given argument is null. In FunC, the value null belongs to the TVM type Null, which represents the absence of a value for certain atomic types. See null values for details.
• touch and ~touch push a variable to the top of the stack.
• at returns the value of a tuple element at the specified position.

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