Built-in Functions

Risor includes this set of default built-in functions. The set of available built-ins is easily customizable, depending on the goals for your project.

all

all(container) bool

Returns true if all objects in the given container are "truthy".

>>> all([true, 1, "ok"])
true
>>> all([true, 0, "ok"])
false

any

any(container) bool

Returns true if any of the objects in the given container are "truthy".

>>> any([false, 0, "ok"])
true
>>> any([false, 0, ""])
false

assert

assert(object, message)

Generates an error if x is "falsy". If a message is provided, it is used as the assertion error message.

>>> assert(1 == 1)                 // no effect
>>> assert(1 == 1, "check failed") // no effect
>>> assert(1 == 2, "check failed") // raises error
check failed
>>> assert(1 == 2)                 // raises error
assertion failed

bool

bool(object) bool

Returns true or false depending on whether the object is considered "truthy". Container types including lists, maps, sets, and strings evaluate to false when empty and true otherwise.

>>> bool(1)
true
>>> bool(0)
false
>>> bool([1])
true
>>> bool([])
false

buffer

buffer(object) buffer

Returns a Buffer object that wraps a Go bytes.Buffer.

>>> buffer(5)
buffer("\x00\x00\x00\x00\x00")
>>> buffer(byte_slice([65, 66, 67]))
buffer("ABC")
>>> string(buffer(byte_slice([65, 66, 67])))
"ABC"

byte_slice

byte_slice(object) byte_slice

Creates a new slice of bytes, which wraps the Go type []byte. If a single argument is provided, it is used as the initial capacity of the slice. If a list of values is provided, the slice is initialized with those values.

>>> byte_slice()
byte_slice("")
>>> byte_slice(5)
byte_slice("\x00\x00\x00\x00\x00")
>>> byte_slice([1, 2, 3])
byte_slice("\x01\x02\x03")
>>> byte_slice([65, 66, 67])
byte_slice("ABC")
>>> byte_slice([65]) + byte_slice([66, 67])
byte_slice("ABC")
>>> string(byte_slice([65, 66, 67]))
"ABC"

byte

byte(object) byte

Returns a Byte object that wraps a Go byte. The Byte type interoperates seamlessly with Ints and Floats.

>>> byte()
0
>>> byte(3)
3
>>> byte("3")
3
>>> byte(3) == 3
true
>>> byte(3) + 5.5
8.5

call

call(function, ...args object) object

Calls the function with given arguments. This is primarily useful in pipe expressions when a function is being passed through the pipe as a variable.

>>> func inc(x) { x + 1 }
>>> call(inc, 99)
100
>>> inc | call(41)
42

cat

cat(path string, ...paths string) string

Similar to the cat command in Unix, this function concatenates the contents of the given file path(s) and returns the result as a string.

Assuming the following file exists:

alice
blake

>>> cat("names.txt")
"alice\nblake\n"

cd

cd(string)

Changes the current working directory to the given path.

>>> cd("/tmp")
>>> os.getwd()
"/tmp"

chr

chr(int) string

Converts an Int to the corresponding unicode rune, which is returned as a String. The ord built-in performs the inverse transformation.

>>> chr(8364)
"€"
>>> chr(97)
"a"

cp

cp(src_path string, dst_path string)

Copies the contents of the source file to the destination file. If the destination file already exists, it is overwritten.

>>> cp("foo.txt", "bar.txt")

decode

decode(object, codec_name string) object

Decodes the given object using the specified codec. The codec_name is a string that may be one of the following values:

• base64
• base32
• hex
• json
• csv
• urlquery

>>> decode("616263", "hex")
byte_slice("abc")
>>> decode("YWJj", "base64")
byte_slice("abc")
>>> decode("a,b,c\n", "csv")
[["a", "b", "c"]]

See additional notes about codecs in the encode section below.

delete

delete(map, key string)

Deletes the item with the specified key from the map. This operation has no effect if the key is not present in the map.

>>> m := {one: 1, two: 2}
{"one": 1, "two": 2}
>>> delete(m, "one")
{"two": 2}
>>> delete(m, "foo")
{"two": 2}

encode

encode(object, codec_name string) object

Encodes the given object using the specified codec. The codec_name is a string that may be one of the following values:

• base64
• base32
• hex
• json
• csv
• urlquery

>>> encode("abc", "hex")
"616263"
>>> encode("abc", "base64")
"YWJj"
>>> encode([["a", "b", "c"]], "csv")
"a,b,c\n"

base64, base32, and hex codecs operate on byte slices or types that can be automatically converted to a byte slice, such as strings. Other codecs may accept different types.

error

error(message string)

Raises an Error containing the given message. A try call can be used to catch the error and handle it. Otherwise, the call stack unwinds and error stops execution of the program.

>>> error("kaboom")
kaboom

fetch

fetch(url string, opts map) http.response

Fetches the content of the given URL and returns an http.response object. The response object provides access to the HTTP status code, headers, and body.

The following options are supported:

>>> r := fetch("https://httpbin.org/get")
>>> r.status_code
200
>>> r.header
{"Connection": ["keep-alive"], "Content-Length": ["14"], "Content-Type": ["text/plain"], "Date": ["Mon, 15 Jan 2024 00:06:56 GMT"], "Server": ["nginx/1.25.1"], "Vary": ["Origin"]}
>>> r.text()
"143.89.131.113"

Visit the http.response documentation for more information about the response object and its attributes.

float_slice

float_slice(object) float_slice

Creates a new slice of floating point values, which wraps the Go type []float64. If a single argument is provided, it is used as the initial capacity of the slice. If a list of values is provided, the slice is initialized with those values.

>>> float_slice()
float_slice([])
>>> float_slice(5)
float_slice([0 0 0 0 0])
>>> float_slice([1.1, 2.2, 3.3])
float_slice([1.1 2.2 3.3])
>>> float_slice([1.1, 2.2, 3.3])[0]
1.1

float

float(object) float

Converts a String or Int object to a Float. An error is generated if the operation fails.

>>> float()
0
>>> float("4.4")
4.4

getattr

getattr(object, name string, default_value object) object

Returns the named attribute from the object, or the default value if the attribute does not exist. The returned attribute is always a Risor object, which may be a function. This is similar to getattr (opens in a new tab) in Python.

>>> l := [1,2,3]
[1, 2, 3]
>>> append := getattr(l, "append")
builtin(list.append)
>>> append(4)
[1, 2, 3, 4]
>>> getattr(l, "unknown", "that doesn't exist")
"that doesn't exist"

getenv

getenv(name string) string

Returns the value of the environment variable with the given name. If the variable is not set, an empty string is returned.

>>> getenv("HOME")
"/home/username"

hash

hash(b byte_slice, algorithm string) byte_slice

Hashes the given byte_slice b using the specified algorithm. If not provided, algorithm defaults to "sha256".

>>> hash("abc")
byte_slice("\xbax\x16\xbf\x8f\x01\xcf\xeaAA@\xde]\xae\"#\xb0\x03a\xa3\x96\x17z\x9c\xb4\x10\xffa\xf2\x00\x15\xad")
>>> hash("a", "md5")
byte_slice("\f\xc1u\xb9\xc0\xf1\xb6\xa81Ù\xe2iw&a")

Available algorithms:

• md5
• sha1
• sha256
• sha512

int

int(object) int

Converts a String or Float to an Int. An error is generated if the operation fails.

>>> int(4.4)
4
>>> int("123")
123

iter

iter(container) iterator

Returns an iterator for the given container object. This can be used to iterate through items in a for loop or interacted with more directly. The returned iterator has next() and entry() methods which are used to move forward and to retrieve the current entry, respectively.

>>> s := {"a", "b", "c"}
>>> iterator := iter(s)
>>> iterator.next()
"a"
>>> iterator.next()
"b"
>>> iterator.entry()
iter_entry("b", true)
>>> iterator.entry().key
"b"
>>> iterator.entry().value
true

jmespath

jmespath(data object, expression string) object

Queries data using the given JMESPath (opens in a new tab) expression. Note the data is provided as the first argument which makes it useful in pipe expressions.

>>> jmespath({"count": 42, "name": "foo"}, "count")
42
>>> [{"name": "a"}, {"name": "b"}] | jmespath("[].name")
["a", "b"]

keys

keys(container) list

Returns a list of all keys for items in the given map or list container.

>>> m := {one: 1, two: 2}
{"one": 1, "two": 2}
>>> keys(m)
["one", "two"]

len

len(container) int

Returns the size of the given container. Container types include:

• String
• List
• Map
• Set
• FloatSlice
• ByteSlice

>>> len("ab")        // string length
2
>>> len([1,2,3])     // list length
3
>>> len({foo:"bar"}) // map length
1
>>> len({1,2,3,4})   // set length
4

list

list(container) list

Returns a new list populated with items from the given container. If a list is provided, a shallow copy of the list is returned. It is also commonly used to convert a set to a list.

>>> s := {"a", "b", "c"}
{"a", "b", "c"}
>>> list(s)
["a", "b", "c"]

ls

ls(path string) list

Lists the contents of the specified directory. If a directory is not provided, the current working directory is used. The returned list contains one DirEntry object for each file or directory in the specified directory.

>>> ls()
[dir_entry(name=file1.txt, type=regular), dir_entry(name=logs, type=dir)]
>>> ls("logs")
[dir_entry(name=logs.txt, type=regular)]

map

map(container) map

Returns a new map which is populated with the items from the given container if one is provided. This behaves similarly to dict in Python.

>>> map()
{}
>>> map([["k1", 1], ["k2", 2]])
{"k1": 1, "k2": 2}
>>> map({"a", "b", "c"}) // converts a set to a map
{"a": true, "b": true, "c": true}

nslookup

nslookup(name string, query_type string = "HOST", resolver_addr string = "")

Look up the given domain name using the specified query type (default "HOST") and resolver address (default "" for system default).

>>> nslookup("google.com")
["172.253.115.138", "172.253.115.100", "172.253.115.139", "172.253.115.113", "172.253.115.101", "172.253.115.102", "2607:f8b0:4004:c08::8b", "2607:f8b0:4004:c08::71", "2607:f8b0:4004:c08::8a", "2607:f8b0:4004:c08::65"]

ord

ord(string) int

Converts a unicode character to the corresponding Int value. The chr built-in performs the inverse transformation. An error is generated if a multi-rune string is provided.

>>> ord("€")
8364
>>> ord("a")
97
>>> chr(ord("€"))
"€"

print

print(args ...object)

Prints the provided objects to stdout after converting them to their String representations. Spaces are inserted between each object and a trailing newline is output. This is a wrapper around fmt.Println.

>>> print(42, "is the answer")
42 is the answer

printf

printf(format string, args ...object)

Printf wraps fmt.Printf in order to print the formatted string and arguments to stdout. In the Risor REPL you will currently not see the printf output unless the string ends in a newline character.

>>> printf("name: %s age: %d\n", "joe", 32)
name: joe age: 32

reversed

reversed(list) list

Returns a new list which is a reversed copy of the provided list.

>>> l := ["a", "b", "c"]
["a", "b", "c"]
>>> reversed(l)
["c", "b", "a"]
>>> l
["a", "b", "c"]

set

set(container) set

Returns a new set containing the items from the given container object.

>>> set("aabbcc")
{"a", "b", "c"}
>>> set([4,4,5])
{4, 5}
>>> set({one:1, two:2})
{"one", "two"}

setenv

setenv(name, value string)

Sets the value of the environment variable with the given name to the provided value. If the variable does not exist, it is created.

>>> setenv("FOO", "bar")
>>> getenv("FOO")
"bar"

sorted

sorted(container) list

Returns a sorted list of items from the given container object.

>>> sorted("cba")
["a", "b", "c"]
>>> sorted([10, 3, -5])
[-5, 3, 10]

sprintf

sprintf(format string, args ...object) string

Wraps fmt.Sprintf to format the string with the provided arguments. Risor objects are converted to their corresponding Go types before being passed to fmt.Sprintf.

>>> sprintf("name: %s age: %d", "fred", 18)
"name: fred age: 18"
>>> sprintf("%v", [1, "a", 3.3])
"[1 a 3.3]"

string

string(object) string

Returns a string representation of the given Risor object.

>>> string({one:1, two:2})
"{\"one\": 1, \"two\": 2}"
>>> string(4.4)
"4.4"
>>> string([1,2,3])
"[1, 2, 3]"

try

try(args ...object) object

Accepts one or more functions which are executed in order until one of them doesn't raise an error and returns that functions return value. If any non-callable object is reached in the provided arguments, that object is returned immediately. Otherwise, if all functions raise errors, nil is returned.

>>> func kaboom() { error("kaboom!") }
>>> try(kaboom)                                      // returns nil
>>> try(kaboom, func() { error("this failed too") }) // returns nil
>>> try(kaboom, "fallback")                          // returns "fallback"
"fallback"
>>> try(42)
42
>>> try(func() { 42 })
42

type

type(object) string

Returns the type name of the given object as a String.

>>> type(1)
"int"
>>> type(2.2)
"float"
>>> type("hi")
"string"
>>> type([])
"list"
>>> type({})
"map"
>>> type({1,2,3})
"set"

unsetenv

unsetenv(name string)

Removes the environment variable with the given name.

>>> setenv("FOO", "bar")
>>> getenv("FOO")
"bar"
>>> unsetenv("FOO")
>>> getenv("FOO")
""