#elvdoc:fn nop
#
# ```elvish
# nop &any-opt= $value...
# ```
#
# Accepts arbitrary arguments and options and does exactly nothing.
#
# Examples:
#
# ```elvish-transcript
# ~> nop
# ~> nop a b c
# ~> nop &k=v
# ```
#
# Etymology: Various languages, in particular NOP in
# [assembly languages](https://en.wikipedia.org/wiki/NOP).

#elvdoc:fn kind-of
#
# ```elvish
# kind-of $value...
# ```
#
# Output the kinds of `$value`s. Example:
#
# ```elvish-transcript
# ~> kind-of lorem [] [&]
# ▶ string
# ▶ list
# ▶ map
# ```
#
# The terminology and definition of "kind" is subject to change.

#elvdoc:fn constantly
#
# ```elvish
# constantly $value...
# ```
#
# Output a function that takes no arguments and outputs `$value`s when called.
# Examples:
#
# ```elvish-transcript
# ~> var f = (constantly lorem ipsum)
# ~> $f
# ▶ lorem
# ▶ ipsum
# ```
#
# The above example is equivalent to simply `var f = { put lorem ipsum }`;
# it is most useful when the argument is **not** a literal value, e.g.
#
# ```elvish-transcript
# ~> var f = (constantly (uname))
# ~> $f
# ▶ Darwin
# ~> $f
# ▶ Darwin
# ```
#
# The above code only calls `uname` once when defining `$f`. In contrast, if
# `$f` is defined as `var f = { put (uname) }`, every time you invoke `$f`,
# `uname` will be called.
#
# Etymology: [Clojure](https://clojuredocs.org/clojure.core/constantly).

#elvdoc:fn call
#
# ```elvish
# call $fn $args $opts
# ```
#
# Calls `$fn` with `$args` as the arguments, and `$opts` as the option. Useful
# for calling a function with dynamic option keys.
#
# Example:
#
# ```elvish-transcript
# ~> var f = {|a &k1=v1 &k2=v2| put $a $k1 $k2 }
# ~> call $f [foo] [&k1=bar]
# ▶ foo
# ▶ bar
# ▶ v2
# ```

#elvdoc:fn resolve
#
# ```elvish
# resolve $command
# ```
#
# Output what `$command` resolves to in symbolic form. Command resolution is
# described in the [language reference](language.html#ordinary-command).
#
# Example:
#
# ```elvish-transcript
# ~> resolve echo
# ▶ <builtin echo>
# ~> fn f { }
# ~> resolve f
# ▶ <closure 0xc4201c24d0>
# ~> resolve cat
# ▶ <external cat>
# ```

#elvdoc:fn eval
#
# ```elvish
# eval $code &ns=$nil &on-end=$nil
# ```
#
# Evaluates `$code`, which should be a string. The evaluation happens in a
# new, restricted namespace, whose initial set of variables can be specified by
# the `&ns` option. After evaluation completes, the new namespace is passed to
# the callback specified by `&on-end` if it is not nil.
#
# The namespace specified by `&ns` is never modified; it will not be affected
# by the creation or deletion of variables by `$code`. However, the values of
# the variables may be mutated by `$code`.
#
# If the `&ns` option is `$nil` (the default), a temporary namespace built by
# amalgamating the local and upvalue scopes of the caller is used.
#
# If `$code` fails to parse or compile, the parse error or compilation error is
# raised as an exception.
#
# Basic examples that do not modify the namespace or any variable:
#
# ```elvish-transcript
# ~> eval 'put x'
# ▶ x
# ~> var x = foo
# ~> eval 'put $x'
# ▶ foo
# ~> var ns = (ns [&x=bar])
# ~> eval &ns=$ns 'put $x'
# ▶ bar
# ```
#
# Examples that modify existing variables:
#
# ```elvish-transcript
# ~> var y = foo
# ~> eval 'set y = bar'
# ~> put $y
# ▶ bar
# ```
#
# Examples that creates new variables and uses the callback to access it:
#
# ```elvish-transcript
# ~> eval 'var z = lorem'
# ~> put $z
# compilation error: variable $z not found
# [ttz 2], line 1: put $z
# ~> var saved-ns = $nil
# ~> eval &on-end={|ns| set saved-ns = $ns } 'var z = lorem'
# ~> put $saved-ns[z]
# ▶ lorem
# ```
#
# Note that when using variables from an outer scope, only those
# that have been referenced are captured as upvalues (see [closure
# semantics](language.html#closure-semantics)) and thus accessible to `eval`:
#
# ```elvish-transcript
# ~> var a b
# ~> fn f {|code| nop $a; eval $code }
# ~> f 'echo $a'
# $nil
# ~> f 'echo $b'
# Exception: compilation error: variable $b not found
# [eval 2], line 1: echo $b
# Traceback: [... omitted ...]
# ```

#elvdoc:fn use-mod
#
# ```elvish
# use-mod $use-spec
# ```
#
# Imports a module, and outputs the namespace for the module.
#
# Most code should use the [use](language.html#importing-modules-with-use)
# special command instead.
#
# Examples:
#
# ```elvish-transcript
# ~> echo 'var x = value' > a.elv
# ~> put (use-mod ./a)[x]
# ▶ value
# ```

#elvdoc:fn deprecate
#
# ```elvish
# deprecate $msg
# ```
#
# Shows the given deprecation message to stderr. If called from a function
# or module, also shows the call site of the function or import site of the
# module. Does nothing if the combination of the call site and the message has
# been shown before.
#
# ```elvish-transcript
# ~> deprecate msg
# deprecation: msg
# ~> fn f { deprecate msg }
# ~> f
# deprecation: msg
# [tty 19], line 1: f
# ~> exec
# ~> deprecate msg
# deprecation: msg
# ~> fn f { deprecate msg }
# ~> f
# deprecation: msg
# [tty 3], line 1: f
# ~> f # a different call site; shows deprecate message
# deprecation: msg
# [tty 4], line 1: f
# ~> fn g { f }
# ~> g
# deprecation: msg
# [tty 5], line 1: fn g { f }
# ~> g # same call site, no more deprecation message
# ```

#elvdoc:fn sleep
#
# ```elvish
# sleep $duration
# ```
#
# Pauses for at least the specified duration. The actual pause duration depends
# on the system.
#
# This only affects the current Elvish context. It does not affect any other
# contexts that might be executing in parallel as a consequence of a command
# such as [`peach`](#peach).
#
# A duration can be a simple [number](language.html#number) (with optional
# fractional value) without an explicit unit suffix, with an implicit unit of
# seconds.
#
# A duration can also be a string written as a sequence of decimal numbers,
# each with optional fraction, plus a unit suffix. For example, "300ms",
# "1.5h" or "1h45m7s". Valid time units are "ns", "us" (or "µs"), "ms", "s",
# "m", "h".
#
# Passing a negative duration causes an exception; this is different from the
# typical BSD or GNU `sleep` command that silently exits with a success status
# without pausing when given a negative duration.
#
# See the [Go documentation](https://golang.org/pkg/time/#ParseDuration) for
# more information about how durations are parsed.
#
# Examples:
#
# ```elvish-transcript
# ~> sleep 0.1    # sleeps 0.1 seconds
# ~> sleep 100ms  # sleeps 0.1 seconds
# ~> sleep 1.5m   # sleeps 1.5 minutes
# ~> sleep 1m30s  # sleeps 1.5 minutes
# ~> sleep -1
# Exception: sleep duration must be >= zero
# [tty 8], line 1: sleep -1
# ```

#elvdoc:fn time
#
# ```elvish
# time &on-end=$nil $callable
# ```
#
# Runs the callable, and call `$on-end` with the duration it took, as a
# number in seconds. If `$on-end` is `$nil` (the default), prints the
# duration in human-readable form.
#
# If `$callable` throws an exception, the exception is propagated after the
# on-end or default printing is done.
#
# If `$on-end` throws an exception, it is propagated, unless `$callable` has
# already thrown an exception.
#
# Example:
#
# ```elvish-transcript
# ~> time { sleep 1 }
# 1.006060647s
# ~> time { sleep 0.01 }
# 1.288977ms
# ~> var t = ''
# ~> time &on-end={|x| set t = $x } { sleep 1 }
# ~> put $t
# ▶ (num 1.000925004)
# ~> time &on-end={|x| set t = $x } { sleep 0.01 }
# ~> put $t
# ▶ (num 0.011030208)
# ```
#
# @cf benchmark

#elvdoc:fn benchmark
#
# ```elvish
# benchmark &min-runs=5 &min-time=1s &on-end=$nil &on-run-end=$nil $callable
# ```
#
# Runs `$callable` repeatedly, and reports statistics about how long each run
# takes.
#
# If the `&on-end` callback is not given, `benchmark` prints the average,
# standard deviation, minimum and maximum of the time it took to run
# `$callback`, and the number of runs. If the `&on-end` callback is given,
# `benchmark` instead calls it with a map containing these metrics, keyed by
# `avg`, `stddev`, `min`, `max` and `runs`. Each duration value (i.e. all
# except `runs`) is given as the number of seconds.
#
# The number of runs is controlled by `&min-runs` and `&min-time`. The
# `$callable` is run at least `&min-runs` times, **and** when the total
# duration is at least `&min-time`.
#
# The `&min-runs` option must be a non-negative integer within the range of the
# machine word.
#
# The `&min-time` option must be a string representing a non-negative duration,
# specified as a sequence of decimal numbers with a unit suffix (the numbers
# may have fractional parts), such as "300ms", "1.5h" and "1h45m7s". Valid time
# units are "ns", "us" (or "µs"), "ms", "s", "m", "h".
#
# If `&on-run-end` is given, it is called after each call to `$callable`, with
# the time that call took, given as the number of seconds.
#
# If `$callable` throws an exception, `benchmark` terminates and propagates the
# exception after the `&on-end` callback (or the default printing behavior)
# finishes. The duration of the call that throws an exception is not passed to
# `&on-run-end`, nor is it included when calculating the statistics for
# `&on-end`. If the first call to `$callable` throws an exception and `&on-end`
# is `$nil`, nothing is printed and any `&on-end` callback is not called.
#
# If `&on-run-end` is given and throws an exception, `benchmark` terminates and
# propagates the exception after the `&on-end` callback (or the default
# printing behavior) finishes, unless `$callable` has already thrown an
# exception
#
# If `&on-end` throws an exception, the exception is propagated, unless
# `$callable` or `&on-run-end` has already thrown an exception.
#
# Example:
#
# ```elvish-transcript
# ~> benchmark { }
# 98ns ± 382ns (min 0s, max 210.417µs, 10119226 runs)
# ~> benchmark &on-end={|m| put $m[avg]} { }
# ▶ (num 9.8e-08)
# ~> benchmark &on-run-end={|d| echo $d} { sleep 0.3 }
# 0.301123625
# 0.30123775
# 0.30119075
# 0.300629166
# 0.301260333
# 301.088324ms ± 234.298µs (min 300.629166ms, max 301.260333ms, 5 runs)
# ```
#
# @cf time

#elvdoc:fn -ifaddrs
#
# ```elvish
# -ifaddrs
# ```
#
# Output all IP addresses of the current host.
#
# This should be part of a networking module instead of the builtin module.