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erl_eval(3erl) | Erlang Module Definition | erl_eval(3erl) |
NAME¶
erl_eval - The Erlang meta interpreter.DESCRIPTION¶
This module provides an interpreter for Erlang expressions. The expressions are in the abstract syntax as returned by erl_parse, the Erlang parser, or io.DATA TYPES¶
bindings() = [{name(), value()}]binding_struct() = orddict:orddict()
A binding structure.
expression() = erl_parse:abstract_expr()expressions() = [erl_parse:abstract_expr()]
As returned by erl_parse:parse_exprs/1 or
io:parse_erl_exprs/2.
expression_list() = [expression()]func_spec() ={Module :: module(), Function :: atom()} | function()lfun_eval_handler() =fun((Name :: atom(),Arguments :: expression_list(),Bindings :: binding_struct()) ->{value,Value :: value(),NewBindings :: binding_struct()})lfun_value_handler() =fun((Name :: atom(), Arguments :: [term()]) ->Value :: value())local_function_handler() ={value, lfun_value_handler()} |{eval, lfun_eval_handler()} |none
Further described in section Local Function Handler in this module
name() = term()nlfun_handler() =fun((FuncSpec :: func_spec(), Arguments :: [term()]) -> term())non_local_function_handler() = {value, nlfun_handler()} | none
Further described in section Non-Local Function Handler in this
module.
value() = term()
EXPORTS¶
add_binding(Name, Value, BindingStruct) -> binding_struct()
Types:
Name = name()
Value = value()
BindingStruct = binding_struct()
Adds binding Name=Value to BindingStruct. Returns an updated
binding structure.
binding(Name, BindingStruct) -> {value, value()} | unbound
Types:
Name = name()
BindingStruct = binding_struct()
Returns the binding of Name in BindingStruct.
bindings(BindingStruct :: binding_struct()) -> bindings()
Returns the list of bindings contained in the binding structure.
del_binding(Name, BindingStruct) -> binding_struct()
Types:
Name = name()
BindingStruct = binding_struct()
Removes the binding of Name in BindingStruct. Returns an updated
binding structure.
expr(Expression, Bindings) -> {value, Value, NewBindings}
expr(Expression, Bindings, LocalFunctionHandler) -> {value, Value, NewBindings}
expr(Expression, Bindings, LocalFunctionHandler, NonLocalFunctionHandler) -> {value, Value, NewBindings}
expr(Expression, Bindings, LocalFunctionHandler, NonLocalFunctionHandler, ReturnFormat) -> {value, Value, NewBindings} | Value
Types:
Expression = expression()
Bindings = binding_struct()
LocalFunctionHandler = local_function_handler()
NonLocalFunctionHandler = non_local_function_handler()
ReturnFormat = none | value
Value = value()
NewBindings = binding_struct()
Evaluates Expression with the set of bindings Bindings.
Expression is an expression in abstract syntax. For an explanation of
when and how to use arguments LocalFunctionHandler and
NonLocalFunctionHandler, see sections Local Function Handler
and Non-Local Function Handler in this module.
Returns {value, Value, NewBindings} by default. If ReturnFormat is
value, only Value is returned.
expr_list(ExpressionList, Bindings) -> {ValueList, NewBindings}
expr_list(ExpressionList, Bindings, LocalFunctionHandler) -> {ValueList, NewBindings}
expr_list(ExpressionList, Bindings, LocalFunctionHandler, NonLocalFunctionHandler) -> {ValueList, NewBindings}
Types:
ExpressionList = expression_list()
Bindings = binding_struct()
LocalFunctionHandler = local_function_handler()
NonLocalFunctionHandler = non_local_function_handler()
ValueList = [ value()]
NewBindings = binding_struct()
Evaluates a list of expressions in parallel, using the same initial bindings for
each expression. Attempts are made to merge the bindings returned from each
evaluation. This function is useful in LocalFunctionHandler, see
section Local Function Handler in this module.
Returns {ValueList, NewBindings}.
exprs(Expressions, Bindings) -> {value, Value, NewBindings}
exprs(Expressions, Bindings, LocalFunctionHandler) -> {value, Value, NewBindings}
exprs(Expressions, Bindings, LocalFunctionHandler, NonLocalFunctionHandler) -> {value, Value, NewBindings}
Types:
Expressions = expressions()
Bindings = binding_struct()
LocalFunctionHandler = local_function_handler()
NonLocalFunctionHandler = non_local_function_handler()
Value = value()
NewBindings = binding_struct()
Evaluates Expressions with the set of bindings Bindings, where
Expressions is a sequence of expressions (in abstract syntax) of a type
that can be returned by io:parse_erl_exprs/2. For an explanation
of when and how to use arguments LocalFunctionHandler and
NonLocalFunctionHandler, see sections Local Function Handler
and Non-Local Function Handler in this module.
Returns {value, Value, NewBindings}
new_bindings() -> binding_struct()
Returns an empty binding structure.
LOCAL FUNCTION HANDLER¶
During evaluation of a function, no calls can be made to local functions. An undefined function error would be generated. However, the optional argument LocalFunctionHandler can be used to define a function that is called when there is a call to a local function. The argument can have the following formats:- {value,Func}:
- This defines a local function handler that is called with:
Func(Name, Arguments)
Name is the name of the local function (an atom) and Arguments is
a list of the evaluated arguments. The function handler returns the
value of the local function. In this case, the current bindings cannot be
accessed. To signal an error, the function handler calls exit/1 with a
suitable exit value.
- {eval,Func}:
- This defines a local function handler that is called with:
Func(Name, Arguments, Bindings)
Name is the name of the local function (an atom), Arguments is a
list of the unevaluated arguments, and Bindings are the current
variable bindings. The function handler returns:
{value,Value,NewBindings}
Value is the value of the local function and NewBindings are the
updated variable bindings. In this case, the function handler must itself
evaluate all the function arguments and manage the bindings. To signal an
error, the function handler calls exit/1 with a suitable exit
value.
- none:
- There is no local function handler.
NON-LOCAL FUNCTION HANDLER¶
The optional argument NonLocalFunctionHandler can be used to define a function that is called in the following cases:- *
- A functional object (fun) is called.
- *
- A built-in function is called.
- *
- A function is called using the M:F syntax, where M and F are atoms or expressions.
- *
- An operator Op/A is called (this is handled as a call to function erlang:Op/A).
- {value,Func}:
- This defines a non-local function handler that is called with:
Func(FuncSpec, Arguments)
FuncSpec is the name of the function on the form {Module,Function}
or a fun, and Arguments is a list of the evaluated arguments.
The function handler returns the value of the function. To signal an error,
the function handler calls exit/1 with a suitable exit value.
- none:
- There is no non-local function handler.
Note:
For calls such as erlang:apply(Fun, Args) or erlang:apply(Module,
Function, Args), the call of the non-local function handler corresponding
to the call to erlang:apply/2,3 itself (Func({erlang, apply}, [Fun,
Args]) or Func({erlang, apply}, [Module, Function, Args])) never
takes place.
The non-local function handler is however called with the evaluated
arguments of the call to erlang:apply/2,3: Func(Fun, Args) or
Func({Module, Function}, Args) (assuming that {Module, Function}
is not {erlang, apply}).
Calls to functions defined by evaluating fun expressions "fun ...
end" are also hidden from non-local function handlers.
The non-local function handler argument is probably not used as frequently as
the local function handler argument. A possible use is to call exit/1
on calls to functions that for some reason are not allowed to be called.
KNOWN LIMITATION¶
Undocumented functions in this module are not to be used.stdlib 3.2 | Ericsson AB |