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The Fift stack can contain values of the following types:
IntegerA TVM signed 257-bit integer.
CellA TVM cell for persistent data storage on TON Blockchain. A cell consists of up to 1023 data bits and up to 4 references to other cells.
SliceA TVM slice is a read-only view of a TVM cell that allows sequential access to the cell’s data and references. A cell can be converted into a slice, extracting stored bits and references without modifying the original cell.
BuilderA TVM builder is a mutable structure used to construct a cell by adding data and references to other cells.
NullThe TVM Null type has exactly one value null. In Fift, null is mostly used to initialize Box’es, hashmaps and lists. Usually denoted by ⊥.
TupleA tuple is an ordered collection of values of any of the Fift types in this list, where each value is not necessarily of the same type. Tuples can be used to represent values of arbitrary algebraic data types and Lisp-style lists.
StringAn UTF-8 string.
BytesAn arbitrary sequence of 8-bit bytes, typically used to represent binary data.
WordListA partially created list of word references, used for creating a new WordDef.
WordDefAn execution token, usually representing the definition of an existing Fift word.
BoxA container occupying one stack slot, that can be used to store one value of any type. Usually used to represent variables.
AtomA simple entity uniquely identified by its name, a string. Can be used to represent identifiers, labels, operation names, tags, and stack markers.
ObjectAn arbitrary C++ object of any class derived from base class td::CntObject. It may be used by Fift extensions to manipulate other data types and interface with other C++ libraries.
The first six types listed above are shared with TVM; the remainder are Fift-specific.
No boolean typeThere is no dedicated Boolean type. Instead, booleans are represented as integers:
  • “false” is 0, “true” is -1, a 257-bit integer with all bits set to 1.
  • Logical operations are performed using bitwise operations.
  • In conditional execution of blocks and loops with exit conditions, any nonzero integer in the conditions is regarded as “true”.
No TVM continuation typeFift does not make use of the TVM continuation type explicitly; instead, if a continuation ends up in the Fift stack, it is manipulated as a value of type Object.Nevertheless, Fift has words for constructing TVM continuations. Refer to TVM continuations in the Fift Assembler page for more details.