lfe_types(7)                                                      lfe_types(7)



NAME
       lfe_types - LFE Types and Functions Specifications

TYPES
       This is a description of the type syntax.

       LFE type                    Erlang type
       ─────────────────────────────────────────────────────
       (none)                      none()
       (any)                       any()
       (atom)                      atom()
       (integer)                   integer()
       (range i1 i2)               I1..I2
       (float)                     float()
       (bitstring m n)             <<_:M,_:_*N>>
       (binary)                    <<_:0,_:_*8>>
       (bitstring)                 <<_:0,_:_*1>>
       ...                         ...
       (lambda any <type>)         fun((...) -> <type>)
       (lambda () <type>)          fun(() -> <type>)
       (lambda (<tlist>) <type>)   fun((<tlist>) -> <type>)
       (map)                       map()
       #M()                        #{}
       #M(<key> <value> ...)       #{<pairlist>}
       (tuple)                     tuple()
       #()                         {}
       #(<tlist>)                  {<tlist>}
       (UNION <tlist>)             <type> | <type>

       Apart  from the predefined types in the Erlang type system we also have
       the following predefined types which cannot be redefined: UNION,  call,
       lambda and range.  The usage of bitstring, tuple and map have also been
       extended.

       Note that the type #M() is the empty map and the type #() is the  empty
       tuple.   We  can  still  use the older (map <key valuelist>) and (tuple
       <tlist>) formats when declaring types for maps and tuples.

       The general form of bitstrings is (bitstring m n) which denotes a  bit‐
       string  which starts with m bits and continues with segments of n bits.
       (binary) is a short form for a sequence of bytes while (bitstring) is a
       short  form  for  a sequence of bits.  There is currently no short form
       for an empty binary, (bitstring 0 0) must be used.

   Type Declarations of User-Defined Types
       (deftype (type-name) type-def)

       (defopaque (type-name) type-def)

       (deftype (type-name par1 par2) type-def)

       (defopaque (type-name par1 par2) type-def)

       For unparameterised types the parentheses around the type name are  op‐
       tional.  An example:

              (deftype foo (tuple 'foo (integer) (list)))

              (deftype bar (tuple 'bar (integer) (list)))

   Type Information in Record Declarations
       (defrecord rec (field1 default1 type1) (field2 default2) (field3))

       Fields with type annotations MUST give a default value and fields with‐
       out type annotations get the default type (any).

SPECIFICATIONS
   Type specifications of User-Defined Functions
       (defspec (func-name arity) function-spec ...)

       where

              function-spec = (arg-type-list ret-type)
              function-spec = (arg-type-list ret-type constraint-list)
              arg-type-list = (arg-type ...)
              constraint-list = (constraint ...)
              constraint = (var var-type)

       For multiple types add more function specs.  The parentheses around the
       function name and the arity are optional.  For example from the docs:

              (defspec foo ([(pos_integer)] (pos_integer)))

              (defspec (foo 1)
                ([(pos_integer)] (pos_integer))
                ([(integer)] (integer)))

              (defspec (remove-if 2)
                ([(lambda ((any)) (boolean)) (list)] (list)))

       Or with constraints:

              (defspec id ((X) X ((X (tuple)))))

              (defspec (foo 1)
                ([(tuple X (integer))] X ((X (atom))))
                ([(list Y)] Y ((Y (number)))))

              (defspec (remove-if 2)
                ([pred (list)] (list) [(pred (lambda ((any)) (boolean)))]))

       Note  that  a  constraint variable doesn’t need to start with an upper-
       case like an Erlang variable, though in some case it may be  easier  to
       read.

       Note we are using the alternate list form with [ ] instead of parenthe‐
       ses to make it easier to see the function arguments.

Types and function specifications in the module definition
       Types can also be defined in the module declaration, for example:

              (defmodule this-module
                ...
                (type ((foo-type) (tuple 'foo (integer) (list)))
                      ((bar-type) (tuple 'bar (integer) (list))))
                (spec ((foo 1) ([(integer)] (foo-type)))
                      ((id 1) ([x] x ((x (tuple))))))
                ...)

AUTHORS
       Robert Virding.



                                     2021                         lfe_types(7)
