Module `std.debug`

Additions to the core debug module.

The module table returned by std.debug also contains all of the entries from the core debug table. An hygienic way to import this module, then, is simply to override the core debug locally:

local debug = require "std.debug"

The behaviour of the functions in this module are controlled by the value of the global _DEBUG. Not setting _DEBUG prior to requiring any of stdlib's modules is equivalent to having _DEBUG = true.

The first line of Lua code in production quality projects that use stdlib should be either:

_DEBUG = false

or alternatively, if you need to be careful not to damage the global environment:

local init = require "std.debug_init"
init._DEBUG = false

This mitigates almost all of the overhead of argument typechecking in stdlib API functions.

Functions

DEPRECATED (version, name[, extramsg], fn)	Provide a deprecated function definition according to _DEBUG.deprecate.
DEPRECATIONMSG (version, name[, extramsg], level)	Format a deprecation warning message.
argcheck (name, i, expected, actual[, level=2])	Check the type of an argument against expected types.
argerror (name, i[, extramsg[, level=1]])	Raise a bad argument error.
argscheck (decl, inner)	Wrap a function definition with argument type and arity checking.
debug ()	Equivalent to calling `debug.say (1, ...)`
extramsg_mismatch (expected, actual[, index])	Format a type mismatch error.
parsetypes (types)	Compact permutation list into a list of valid types at each argument.
say ([n=1], ...)	Print a debugging message to `io.stderr`.
trace (event)	Trace function calls.

Tables

_DEBUG

Control std.debug function behaviour.

Fields

extramsg_toomany	Format a too many things error.
getfenv	Extend `debug.getfenv` to unwrap functables correctly.
resulterror	Raise a bad result error.
setfenv	Extend `debug.setfenv` to unwrap functables correctly.
typesplit	Split a typespec string into a table of normalized type names.

Functions

Methods

DEPRECATED (version, name[, extramsg], fn)

Provide a deprecated function definition according to _DEBUG.deprecate. You can check whether your covered code uses deprecated functions by setting _DEBUG.deprecate to true before loading any stdlib modules, or silence deprecation warnings by setting _DEBUG.deprecate = false.

Parameters:

version string first deprecation release version
name string function name for automatic warning message
extramsg string additional warning text (optional)
fn func deprecated function

Returns:

Usage:

M.op = DEPRECATED ("41", "'std.functional.op'", std.operator)

DEPRECATIONMSG (version, name[, extramsg], level)

Format a deprecation warning message.

Parameters:

version string first deprecation release version
name string function name for automatic warning message
extramsg string additional warning text (optional)
level int call stack level to blame for the error

Returns:

string

Usage:

io.stderr:write (DEPRECATIONMSG ("42", "multi-argument 'module.fname'", 2))

argcheck (name, i, expected, actual[, level=2])

Check the type of an argument against expected types. Equivalent to luaL_argcheck in the Lua C API.

Call argerror if there is a type mismatch.

Argument actual must match one of the types from in expected, each of which can be the name of a primitive Lua type, a stdlib object type, or one of the special options below:

#table    accept any non-empty table
any       accept any non-nil argument type
file      accept an open file object
function  accept a function, or object with a __call metamethod
int       accept an integer valued number
list      accept a table where all keys are a contiguous 1-based integer range
#list     accept any non-empty list
object    accept any std.Object derived type
:foo      accept only the exact string ":foo", works for any :-prefixed string

The :foo format allows for type-checking of self-documenting boolean-like constant string parameters predicated on nil versus :option instead of false versus true. Or you could support both:

argcheck ("table.copy", 2, "boolean|:nometa|nil", nometa)

A very common pattern is to have a list of possible types including "nil" when the argument is optional. Rather than writing long-hand as above, prepend a question mark to the list of types and omit the explicit "nil" entry:

argcheck ("table.copy", 2, "?boolean|:nometa", predicate)

Normally, you should not need to use the level parameter, as the default is to blame the caller of the function using argcheck in error messages; which is almost certainly what you want.

Parameters:

name string function to blame in error message
i int argument number to blame in error message
expected string specification for acceptable argument types
actual argument passed
level int call stack level to blame for the error (default 2)

Usage:

 local function case (with, branches)
   argcheck ("std.functional.case", 2, "#table", branches)
   ...

argerror (name, i[, extramsg[, level=1]])

Raise a bad argument error. Equivalent to luaL_argerror in the Lua C API. This function does not return. The level argument behaves just like the core error function.

Parameters:

name string function to callout in error message
i int argument number
extramsg string additional text to append to message inside parentheses (optional)
level int call stack level to blame for the error (default 1)

Usage:

 local function slurp (file)
   local h, err = input_handle (file)
   if h == nil then argerror ("std.io.slurp", 1, err, 2) end
   ...

argscheck (decl, inner)

Wrap a function definition with argument type and arity checking. In addition to checking that each argument type matches the corresponding element in the types table with argcheck, if the final element of types ends with an ellipsis, remaining unchecked arguments are checked against that type:

 format = argscheck ("string.format (string, ?any...)", string.format)

A colon in the function name indicates that the argument type list does not have a type for self:

 format = argscheck ("string:format (?any...)", string.format)

If an argument can be omitted entirely, then put its type specification in square brackets:

 insert = argscheck ("table.insert (table, [int], ?any)", table.insert)

Similarly return types can be checked with the same list syntax as arguments:

 len = argscheck ("string.len (string) => int", string.len)

Additionally, variant return type lists can be listed like this:

 open = argscheck ("io.open (string, ?string) => file or nil, string",
                   io.open)

Parameters:

decl string function type declaration string
inner func function to wrap with argument checking

Usage:

 local case = argscheck ("std.functional.case (?any, #table) => [any...]",
   function (with, branches)
     ...
 end)

debug ()

Equivalent to calling debug.say (1, ...)

Usage:

 local debug = require "std.debug"
 debug "oh noes!"

extramsg_mismatch (expected, actual[, index])

Format a type mismatch error.

Parameters:

expected string a pipe delimited list of matchable types
actual the actual argument to match with
index number erroring container element index (optional)

Returns:

string

extramsg

argerror

Usage:

   if fmt ~= nil and type (fmt) ~= "string" then
     argerror ("format", 1, extramsg_mismatch ("?string", fmt))
   end

parsetypes (types)

Compact permutation list into a list of valid types at each argument. Eliminate bracketed types by combining all valid types at each position for all permutations of typelist.

Parameters:

types list a normalized list of type names

Returns:

list

say ([n=1], ...)

Print a debugging message to io.stderr. Display arguments passed through std.tostring and separated by tab characters when _DEBUG is true and n is 1 or less; or _DEBUG.level is a number greater than or equal to n. If _DEBUG is false or nil, nothing is written.

Parameters:

n int debugging level, smaller is higher priority (default 1)
... objects to print (as for print)

Usage:

 local _DEBUG = require "std.debug_init"._DEBUG
 _DEBUG.level = 3
 say (2, "_DEBUG table contents:", _DEBUG)

trace (event)

Trace function calls. Use as debug.sethook (trace, "cr"), which is done automatically when _DEBUG.call is set. Based on test/trace-calls.lua from the Lua distribution.

Parameters:

event string event causing the call

Usage:

 _DEBUG = { call = true }
 local debug = require "std.debug"

Tables

_DEBUG

Control std.debug function behaviour. To declare debugging state, set _DEBUG either to false to disable all runtime debugging; to any "truthy" value (equivalent to enabling everything except call, or as documented below.

Fields:

argcheck boolean honor argcheck and argscheck calls (default true)
call boolean do call trace debugging (default false)
deprecate if false, deprecated APIs are defined, and do not issue deprecation warnings when used; if nil issue a deprecation warning each time a deprecated api is used; any other value causes deprecated APIs not to be defined at all (default nil)
level int debugging level (default 1)

Usage:

_DEBUG = { argcheck = false, level = 9 }

Fields

extramsg_toomany

Format a too many things error.

bad string the thing there are too many of
expected int maximum number of bad things expected
actual int actual number of bad things that triggered the error

Usage:

   if maxn (argt) > 7 then
     argerror ("sevenses", 8, extramsg_toomany ("argument", 7, maxn (argt)))
   end

getfenv

Extend debug.getfenv to unwrap functables correctly.

fn int, function or functable target function, or stack level

resulterror

Raise a bad result error. Like argerror for bad results. This function does not return. The level argument behaves just like the core error function.

name string function to callout in error message
i int argument number
extramsg string additional text to append to message inside parentheses (optional)
level int call stack level to blame for the error (default 1)

Usage:

 local function slurp (file)
   local h, err = input_handle (file)
   if h == nil then argerror ("std.io.slurp", 1, err, 2) end
   ...

setfenv

Extend debug.setfenv to unwrap functables correctly.

fn function or functable target function
env table new function environment

typesplit

Split a typespec string into a table of normalized type names.

either string or table "?bool|:nometa" or {"boolean", ":nometa"}

stdlib 41.2.2

Contents

Modules

Classes

Module std.debug

Functions

Tables

Fields

Functions

Parameters:

Returns:

Usage:

Parameters:

Returns:

Usage:

Parameters:

Usage:

Parameters:

See also:

Usage:

Parameters:

Usage:

See also:

Usage:

Parameters:

Returns:

See also:

Usage:

Parameters:

Returns:

Parameters:

Usage:

Parameters:

Usage:

Tables

Fields:

Usage:

Fields

See also:

Usage:

Usage:

Module `std.debug`