▼TOML Config:   Configuration Languages for Racket
►3 Appendix
On this page:
3.1 Complete TOML Syntax demo
3.2 Demo language
9.0.0.6
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3 Appendix🔗ℹ

3.1 Complete TOML Syntax demo🔗ℹ

Below is a #lang toml/config module which makes comprehensive use of all forms of TOML syntax, followed by the a readout of the resulting hash table bound to toml.

#lang toml/config
 
# Comprehensive TOML syntax test file
 
# ================================================
# Top-level key-value pairs
 
bare_key = "value"
bare-key-with-dashes = "value"
bare_key_with_underscores = "value"
1234 = "bare keys can be numeric"
"quoted key with spaces" = "value"
'literal quoted key' = "value"
"" = "empty key is valid"
 
dotted.key.example = "creates nested tables implicitly"
dotted."quoted".'mixed' = "whitespace around dots is allowed"
 
# ================================================
# String types
 
basic_string = "I'm a basic string with \t tab and \n newline"
escape_sequences = "backslash: \\ quote: \" tab: \t newline: \n carriage: \r"
unicode_escape = "Greek: \u03B1\u03B2\u03B3 Emoji: \U0001F600"
literal_string = 'No escapes here: \t \n \\ are literal'
literal_with_quotes = 'Can contain "double quotes" freely'
 
multiline_basic = """
Roses are red
Violets are blue"""
 
multiline_basic_escaped = """\
    The quick brown \
    fox jumps over \
    the lazy dog.\
    """
 
multiline_literal = '''
Here is some text.
Backslashes \ are literal.
No escaping "whatsoever".
'''
 
multiline_with_quotes = """Here are two quotes: "". Here are three: ""\"."""
multiline_literal_quotes = '''Here are two apostrophes: ''.'''
 
# Line-ending backslash trims whitespace
trimmed = """\
       Trim this      \
       and this too   \
       """
 
# ================================================
# Integer types  
 
positive_int = 42
negative_int = -17
explicit_positive = +99
zero = 0
 
# Underscores for readability
large_number = 1_000_000
grouped = 5_349_221
indian_grouping = 1_00_00_000
 
# Different bases
hex_lowercase = 0xdeadbeef
hex_uppercase = 0xDEADBEEF
hex_mixed = 0xDeAdBeEf
octal = 0o755
binary = 0b11010110
 
hex_with_underscores = 0xdead_beef
octal_with_underscores = 0o7_5_5
binary_with_underscores = 0b1101_0110
 
# ================================================
# Float types
 
float_simple = 3.14
float_negative = -0.001
float_explicit_positive = +1.23
 
# Exponent notation
exponent_lower = 5e+22
exponent_upper = 1E6
exponent_negative = 6.626e-34
exponent_explicit_positive = 1e+1_000
 
# Combined
full_float = -3.14159e-10
 
# Underscores in floats
float_underscored = 9_224_617.445_991_228
 
# Special float values
positive_infinity = inf
negative_infinity = -inf
explicit_positive_inf = +inf
not_a_number = nan
positive_nan = +nan
negative_nan = -nan
 
# ================================================
# Boolean types
 
bool_true = true
bool_false = false
 
# ================================================
# Date and time types
 
# Offset date-time (full RFC 3339)
odt_zulu = 1979-05-27T07:32:00Z
odt_offset = 1979-05-27T00:32:00-07:00
odt_with_fractional = 1979-05-27T00:32:00.999999-07:00
odt_lowercase_t = 1979-05-27t07:32:00z
odt_space_separator = 1979-05-27 07:32:00Z
 
# Local date-time (no timezone)
ldt_simple = 1979-05-27T07:32:00
ldt_fractional = 1979-05-27T00:32:00.999999
 
# Local date
ld = 1979-05-27
 
# Local time
lt_simple = 07:32:00
lt_fractional = 00:32:00.999999
 
# ================================================
# Arrays
 
# Simple arrays
integers = [1, 2, 3]
colors = ["red", "yellow", "green"]
floats = [1.1, 2.2, 3.3]
booleans = [true, false, true]
 
# Nested arrays
nested_arrays = [[1, 2], [3, 4, 5]]
nested_mixed = [[1, 2], ["a", "b", "c"]]
 
# Multi-line arrays
hosts = [
    "alpha",
    "omega",
]
 
# With trailing commas
numbers_trailing = [
    1,
    2,
    3,
]
 
# Comments in arrays
commented_array = [
    1,  # first
    2,  # second
    # comment on its own line
    3,  # third
]
 
# Mixed content array (arrays of different typed arrays)
mixed_nested = [
    [1, 2, 3],
    [1.0, 2.0, 3.0],
    ["one", "two", "three"],
]
 
# Empty array
empty = []
 
# Array with complex content
dates = [1979-05-27T07:32:00Z, 1979-05-27]
 
# ================================================
# Standard tables
 
[server]
host = "localhost"  # inline comment
port = 8080
 
[server.limits]    # dotted table name
max_connections = 100
timeout = 30.5
 
[database]
enabled = true
ports = [8000, 8001, 8002]
data = [["delta", "phi"], [3.14]]
 
# Table with quoted key
["table with spaces"]
key = "value"
 
['literal table name']
key = "value"
 
[deeply.nested."quoted key".table]
value = 42
 
# Super-table defined after sub-table
[animal]
type = "mammal"
 
[animal.dog]
breed = "poodle"
 
[animal.dog.tater]
name = "Tater Tot"
 
# ================================================
# Inline tables
 
point = {x = 1, y = 2}
point3d = {x = 1, y = 2, z = 3}
 
# Inline table with various value types
mixed_inline = {name = "Widget", price = 9.99, in_stock = true}
 
# Nested inline tables
nested_inline = {outer = {inner = {value = "deep"}}}
 
# Inline table with array
with_array = {tags = ["a", "b", "c"]}
 
# Complex inline
person = {name = "Tom", dob = 1979-05-27, address = {city = "NYC", zip = "10001"}}
 
# Empty inline table
empty_inline = {}
 
# ================================================
# Array of tables
 
[[products]]
name = "Hammer"
sku = 738594937
 
[[products]]  # another element in the products array
name = "Nail"
sku = 284758393
color = "gray"
 
[[products]]
name = "Wrench"
sku = 967294032
colors = ["red", "blue", "green"]
 
# Nested array of tables
[[fruits]]
name = "apple"
 
[[fruits.varieties]]
name = "red delicious"
 
[[fruits.varieties]]
name = "granny smith"
 
[[fruits]]
name = "banana"
 
[[fruits.varieties]]
name = "plantain"
 
# Array of tables with sub-tables
[[servers]]
name = "alpha"
 
[servers.network]
ip = "10.0.0.1"
port = 8080
 
[[servers]]
name = "beta"
 
[servers.network]
ip = "10.0.0.2"
port = 8081
 
# ================================================
# Edge cases and less common syntax
 
# Keys that look like other types
true_key = "not a boolean, this is a key"
false_key = "also a key"
123e45 = "looks like a float but it's a key"
inf_key = "inf as a key"
nan_key = "nan as a key"
 
# Unicode in keys
"ʎǝʞ ǝpoɔıun" = "upside down"
"日本語" = "Japanese"
"emoji🎉key" = "celebration"
 
# Whitespace variations
key_no_spaces="compact"
key_lots_of_spaces    =     "spread out"
 
# Table with all quoted parts
["one"."two"."three"]
value = "fully quoted path"
 
# Mix of bare and quoted in dotted key
bare."with spaces".more = "mixed dotted key"
 
# Very long string for testing
long_string = "Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris."
 
# String with all escape sequences
all_escapes = "backslash:\\, quote:\", backspace:\b, tab:\t, newline:\n, formfeed:\f, carriage:\r"
 
# Boundary numbers
max_safe_int = 9_007_199_254_740_991
min_int = -9_223_372_036_854_775_808
tiny_float = 1e-400
huge_float = 1e+400

Example:
> toml

'#hasheq((|| . "empty key is valid")

         (|1234| . "bare keys can be numeric")

         (animal

          .

          #hasheq((dog

                   .

                   #hasheq((breed . "poodle")

                           (tater

                            .

                            #hasheq((empty_inline . #hasheq())

                                    (mixed_inline

                                     .

                                     #hasheq((in_stock . #t)

                                             (name . "Widget")

                                             (price . 9.99)))

                                    (name . "Tater Tot")

                                    (nested_inline

                                     .

                                     #hasheq((outer

                                              .

                                              #hasheq((inner

                                                       .

                                                       #hasheq((value

                                                                .

                                                                "deep")))))))

                                    (person

                                     .

                                     #hasheq((address

                                              .

                                              #hasheq((city . "NYC")

                                                      (zip . "10001")))

                                             (dob . #<date 1979-05-27>)

                                             (name . "Tom")))

                                    (point . #hasheq((x . 1) (y . 2)))

                                    (point3d

                                     .

                                     #hasheq((x . 1) (y . 2) (z . 3)))

                                    (with_array

                                     .

                                     #hasheq((tags . ("a" "b" "c"))))))))

                  (type . "mammal")))

         (bare-key-with-dashes . "value")

         (bare_key . "value")

         (bare_key_with_underscores . "value")

         (basic_string . "I'm a basic string with \t tab and \n newline")

         (binary . 214)

         (binary_with_underscores . 214)

         (bool_false . #f)

         (bool_true . #t)

         (booleans . (#t #f #t))

         (colors . ("red" "yellow" "green"))

         (commented_array . (1 2 3))

         (database

          .

          #hasheq((data . (("delta" "phi") (3.14)))

                  (enabled . #t)

                  (ports . (8000 8001 8002))))

         (dates . (#<moment 1979-05-27T07:32:00Z> #<date 1979-05-27>))

         (deeply

          .

          #hasheq((nested

                   .

                   #hasheq((|quoted key|

                            .

                            #hasheq((table . #hasheq((value . 42)))))))))

         (dotted

          .

          #hasheq((key

                   .

                   #hasheq((example . "creates nested tables implicitly")))

                  (quoted

                   .

                   #hasheq((mixed . "whitespace around dots is allowed")))))

         (empty . ())

         (escape_sequences

          .

          "backslash: \\ quote: \" tab: \t newline: \n carriage: \r")

         (explicit_positive . 99)

         (explicit_positive_inf . +inf.0)

         (exponent_explicit_positive . +inf.0)

         (exponent_lower . 5e+22)

         (exponent_negative . 6.626e-34)

         (exponent_upper . 1000000.0)

         (float_explicit_positive . 1.23)

         (float_negative . 0.1)

         (float_simple . 3.14)

         (float_underscored . 9224617.445991227)

         (floats . (1.1 2.2 3.3))

         (fruits

          .

          (#hasheq((name . "apple")

                   (varieties

                    .

                    (#hasheq((name . "red delicious"))

                     #hasheq((name . "granny smith")))))

           #hasheq((name . "banana")

                   (varieties . (#hasheq((name . "plantain")))))))

         (full_float . -3.14159e-10)

         (grouped . 5349221)

         (hex_lowercase . 3735928559)

         (hex_mixed . 3735928559)

         (hex_uppercase . 3735928559)

         (hex_with_underscores . 3735928559)

         (hosts . ("alpha" "omega"))

         (indian_grouping . 10000000)

         (integers . (1 2 3))

         (large_number . 1000000)

         (ld . #<date 1979-05-27>)

         (ldt_fractional . #<datetime 1979-05-27T00:32:00.999999>)

         (ldt_simple . #<datetime 1979-05-27T07:32:00>)

         (|literal quoted key| . "value")

         (|literal table name| . #hasheq((key . "value")))

         (literal_string . "No escapes here: \\t \\n \\\\ are literal")

         (literal_with_quotes . "Can contain \"double quotes\" freely")

         (lt_fractional . #<time 00:32:00.999999>)

         (lt_simple . #<time 07:32:00>)

         (mixed_nested . ((1 2 3) (1.0 2.0 3.0) ("one" "two" "three")))

         (multiline_basic . "Roses are red\nViolets are blue")

         (multiline_basic_escaped

          .

          "The quick brown fox jumps over the lazy dog.")

         (multiline_literal

          .

          "Here is some text.\nBackslashes \\ are literal.\nNo escaping \"whatsoever\".\n")

         (multiline_literal_quotes . "Here are two apostrophes: ''.")

         (multiline_with_quotes

          .

          "Here are two quotes: \"\". Here are three: \"\"\".")

         (negative_infinity . -inf.0)

         (negative_int . -17)

         (negative_nan . +nan.0)

         (nested_arrays . ((1 2) (3 4 5)))

         (nested_mixed . ((1 2) ("a" "b" "c")))

         (not_a_number . +nan.0)

         (numbers_trailing . (1 2 3))

         (octal . 493)

         (octal_with_underscores . 493)

         (odt_lowercase_t . #<moment 1979-05-27T07:32:00Z>)

         (odt_offset . #<moment 1979-05-27T00:32:00-07:00>)

         (odt_space_separator . #<moment 1979-05-27T07:32:00Z>)

         (odt_with_fractional . #<moment 1979-05-27T00:32:00.999999-07:00>)

         (odt_zulu . #<moment 1979-05-27T07:32:00Z>)

         (one

          .

          #hasheq((two

                   .

                   #hasheq((three

                            .

                            #hasheq((all_escapes

                                     .

                                     "backslash:\\, quote:\", backspace:\b, tab:\t, newline:\n, formfeed:\f, carriage:\r")

                                    (bare

                                     .

                                     #hasheq((|with spaces|

                                              .

                                              #hasheq((more

                                                       .

                                                       "mixed dotted key")))))

                                    (huge_float . +inf.0)

                                    (long_string

                                     .

                                     "Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris.")

                                    (max_safe_int . 9007199254740991)

                                    (min_int . -9223372036854775808)

                                    (tiny_float . 0.0)

                                    (value . "fully quoted path")))))))

         (positive_infinity . +inf.0)

         (positive_int . 42)

         (positive_nan . +nan.0)

         (products

          .

          (#hasheq((name . "Hammer") (sku . 738594937))

           #hasheq((color . "gray") (name . "Nail") (sku . 284758393))

           #hasheq((colors . ("red" "blue" "green"))

                   (name . "Wrench")

                   (sku . 967294032))))

         (|quoted key with spaces| . "value")

         (server

          .

          #hasheq((host . "localhost")

                  (limits . #hasheq((max_connections . 100) (timeout . 30.5)))

                  (port . 8080)))

         (servers

          .

          (#hasheq((name . "alpha")

                   (network . #hasheq((ip . "10.0.0.1") (port . 8080))))

           #hasheq((name . "beta")

                   (network

                    .

                    #hasheq((|123e45| . "looks like a float but it's a key")

                            (emoji🎉key . "celebration")

                            (false_key . "also a key")

                            (inf_key . "inf as a key")

                            (ip . "10.0.0.2")

                            (key_lots_of_spaces . "spread out")

                            (key_no_spaces . "compact")

                            (nan_key . "nan as a key")

                            (port . 8081)

                            (true_key . "not a boolean, this is a key")

                            (|ʎǝʞ ǝpoɔıun| . "upside down")

                            (日本語 . "Japanese"))))))

         (|table with spaces| . #hasheq((key . "value")))

         (trimmed . "Trim this      and this too   ")

         (unicode_escape . "Greek: αβγ Emoji: 😀")

         (zero . 0))

3.2 Demo language🔗ℹ

 (require toml/config/demo) package: toml-config

This is a DSL installed alongside these docs for demonstration purposes. Its definition is shown below:

"toml/config/demo.rkt"

#lang racket/base
 
(module reader toml/config/custom
 #:schema ([title string? required]
           [port (integer-in 1 65535) (optional 8080)]))
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