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erl_eval(3erl) | Erlang Module Definition | erl_eval(3erl) |
NAME¶
erl_eval - The Erlang Meta InterpreterDESCRIPTION¶
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 below.
name() = term()nlfun_handler() =fun((FuncSpec :: func_spec(), Arguments :: [term()]) -> term())non_local_function_handler() = {value, nlfun_handler()} | none
Further described below.
value() = term()
EXPORTS¶
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
which may be returned by io:parse_erl_exprs/2. See below for an
explanation of how and when to use the arguments LocalFunctionHandler
and NonLocalFunctionHandler.
Returns {value, Value, NewBindings}
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. See below for an
explanation of how and when to use the arguments LocalFunctionHandler
and NonLocalFunctionHandler.
Returns {value, Value, NewBindings} by default. But if the
ReturnFormat is value only the 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 the LocalFunctionHandler. See
below.
Returns {ValueList, NewBindings}.
new_bindings() -> binding_struct()
Returns an empty binding structure.
bindings(BindingStruct :: binding_struct()) -> bindings()
Returns the list of bindings contained in the binding structure.
binding(Name, BindingStruct) -> {value, value()} | unbound
Types:
Name = name()
BindingStruct = binding_struct()
Returns the binding of Name in BindingStruct.
add_binding(Name, Value, BindingStruct) -> binding_struct()
Types:
Name = name()
Value = value()
BindingStruct = binding_struct()
Adds the binding Name = Value to BindingStruct. Returns an updated
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.
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 may be used to define a function which 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 which 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, it is not possible to access the
current bindings. To signal an error, the function handler just calls
exit/1 with a suitable exit value.
- {eval,Func}:
- This defines a local function handler which 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 just calls exit/1 with a suitable exit
value.
- none:
- There is no local function handler.
NON-LOCAL FUNCTION HANDLER¶
The optional argument NonlocalFunctionHandler may be used to define a function which 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 the function erlang:Op/A). Exceptions are calls to erlang:apply/2,3; neither of the function handlers will be called for such calls. The argument can have the following formats:- {value,Func}:
- This defines an nonlocal function handler which 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 just calls exit/1 with a suitable exit
value.
- none:
- There is no nonlocal 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])--will
never take place. The non-local function handler will however be 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 nonlocal 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.
BUGS¶
Undocumented functions in erl_eval should not be used.stdlib 2.2 | Ericsson AB |