Angle bracket S-exprs for Records!
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preserves.md
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preserves.md
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# Preserves: an Expressive Data Language
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Tony Garnock-Jones <tonyg@leastfixedpoint.com>
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June 2019. Version 0.0.5.
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August 2019. Version 0.0.6.
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[sexp.txt]: http://people.csail.mit.edu/rivest/Sexp.txt
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[spki]: http://world.std.com/~cme/html/spki.html
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@ -212,11 +212,10 @@ Any `Value` may be preceded by whitespace.
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Atom = Boolean / Float / Double / SignedInteger /
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String / ByteString / Symbol
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Each `Record` is its label-`Value` followed by a parenthesised
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grouping of its field-`Value`s. Whitespace is not permitted between
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the label and the open-parenthesis.
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Each `Record` is an angle-bracket enclosed grouping of its
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label-`Value` followed by its field-`Value`s.
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Record = Value "(" *Value ws ")"
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Record = "<" Value *Value ws ">"
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`Sequence`s are enclosed in square brackets. `Dictionary` values are
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curly-brace-enclosed colon-separated pairs of values. `Set`s are
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@ -236,12 +235,6 @@ or more values enclosed by the tokens `#set{` and
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commas separating, and commas terminating elements or key/value
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pairs within a collection.
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The special cases of records with a single field, which is in turn a
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sequence or dictionary, may be written omitting the parentheses.
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Record =/ Value Sequence
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Record =/ Value Dictionary
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`Boolean`s are the simple literal strings `#true` and `#false`.
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Boolean = %s"#true" / %s"#false"
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@ -356,7 +349,7 @@ double quote mark.
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symstart = ALPHA / sympunct / symunicode
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symcont = ALPHA / sympunct / symunicode / DIGIT / "-"
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sympunct = "~" / "!" / "$" / "%" / "^" / "&" / "*" /
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"?" / "_" / "=" / "+" / "<" / ">" / "/" / "."
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"?" / "_" / "=" / "+" / "/" / "."
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symchar = unescaped / %x22 / escape (escaped / %x7C / %s"u" 4HEXDIG)
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symunicode = <any code point greater than 127 whose Unicode
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category is Lu, Ll, Lt, Lm, Lo, Mn, Mc, Me, Nd,
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@ -541,14 +534,14 @@ zero-length chunks.
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Format B (known length):
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[[ L(F_1...F_m) ]] = header(2,0,m+1) ++ [[L]] ++ [[F_1]] ++...++ [[F_m]]
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[[ <L F_1...F_m> ]] = header(2,0,m+1) ++ [[L]] ++ [[F_1]] ++...++ [[F_m]]
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For `m` fields, `m+1` is supplied to `header`, to account for the
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encoding of the record label.
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Format C (streaming):
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[[ L(F_1...F_m) ]] = open(2,0) ++ [[L]] ++ [[F_1]] ++...++ [[F_m]] ++ close()
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[[ <L F_1...F_m> ]] = open(2,0) ++ [[L]] ++ [[F_1]] ++...++ [[F_m]] ++ close()
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Applications *SHOULD* prefer the known-length format for encoding
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`Record`s.
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@ -569,7 +562,7 @@ be tersely encoded as
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number 4 to the symbol `void`, making
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[[void]] = header(0,1,4) = [0x14]
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[[void()]] = header(2,0,1) ++ [[void]] = [0x81, 0x14]
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[[<void>]] = header(2,0,1) ++ [[void]] = [0x81, 0x14]
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or it may map symbol `person` to placeholder number 102, making
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@ -577,7 +570,7 @@ or it may map symbol `person` to placeholder number 102, making
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and so
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[[person("Dr", "Elizabeth", "Blackwell")]]
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[[<person "Dr" "Elizabeth" "Blackwell">]]
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= header(2,0,4) ++ [[person]] ++ [["Dr"]] ++ [["Elizabeth"]] ++ [["Blackwell"]]
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= [0x84, 0x1F, 0x66] ++ [["Dr"]] ++ [["Elizabeth"]] ++ [["Blackwell"]]
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@ -714,7 +707,7 @@ The functions `binary32(F)` and `binary64(D)` yield big-endian 4- and
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To annotate a `Repr` `r` with some `Value` `v`, prepend `r` with
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`[0x05] ++ [[v]]`.
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For example, the `Repr` corresponding to textual syntax `@a @b []`,
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For example, the `Repr` corresponding to textual syntax `@a@b[]`,
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i.e. an empty sequence annotated with two symbols, `a` and `b`, is
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[[ @a @b [] ]]
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@ -734,8 +727,8 @@ placeholder number 0 to symbol `discard`, 1 to `capture`, and 2 to
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| Value | Encoded byte sequence |
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|---------------------------------------------------|-------------------------------------------------------------------------------------|
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| `capture(discard())` | 82 11 81 10 |
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| `observe(speak(discard(), capture(discard())))` | 82 12 83 75 's' 'p' 'e' 'a' 'k' 81 10 82 11 81 11 |
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| `<capture <discard>>` | 82 11 81 10 |
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| `<observe <speak <discard> <capture <discard>>>>` | 82 12 83 75 's' 'p' 'e' 'a' 'k' 81 10 82 11 81 11 |
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| `[1 2 3 4]` (format B) | 94 31 32 33 34 |
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| `[1 2 3 4]` (format C) | 29 31 32 33 34 04 |
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| `[-2 -1 0 1]` | 94 3E 3F 30 31 |
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@ -754,7 +747,7 @@ placeholder number 0 to symbol `discard`, 1 to `capture`, and 2 to
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The next example uses a non-`Symbol` label for a record.[^extensibility2] The `Record`
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[titled person 2 thing 1](101, "Blackwell", date(1821 2 3), "Dr")
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<[titled person 2 thing 1] 101 "Blackwell" <date 1821 2 3> "Dr">
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encodes to
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@ -982,16 +975,16 @@ such media types following the general rules for ordering of
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| Value | Encoded hexadecimal byte sequence |
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|--------------------------------------------|-------------------------------------------------------------------------------------------------------------------|
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| `mime(application/octet-stream #"abcde")` | 83 74 6D 69 6D 65 7F 18 61 70 70 6C 69 63 61 74 69 6F 6E 2F 6F 63 74 65 74 2D 73 74 72 65 61 6D 65 61 62 63 64 65 |
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| `mime(text/plain #"ABC")` | 83 74 6D 69 6D 65 7A 74 65 78 74 2F 70 6C 61 69 6E 63 41 42 43 |
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| `mime(application/xml #"<xhtml/>")` | 83 74 6D 69 6D 65 7F 0F 61 70 70 6C 69 63 61 74 69 6F 6E 2F 78 6D 6C 68 3C 78 68 74 6D 6C 2F 3E |
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| `mime(text/csv #"123,234,345")` | 83 74 6D 69 6D 65 78 74 65 78 74 2F 63 73 76 6B 31 32 33 2C 32 33 34 2C 33 34 35 |
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| `<mime application/octet-stream #"abcde">` | 83 74 6D 69 6D 65 7F 18 61 70 70 6C 69 63 61 74 69 6F 6E 2F 6F 63 74 65 74 2D 73 74 72 65 61 6D 65 61 62 63 64 65 |
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| `<mime text/plain #"ABC">` | 83 74 6D 69 6D 65 7A 74 65 78 74 2F 70 6C 61 69 6E 63 41 42 43 |
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| `<mime application/xml #"<xhtml/>">` | 83 74 6D 69 6D 65 7F 0F 61 70 70 6C 69 63 61 74 69 6F 6E 2F 78 6D 6C 68 3C 78 68 74 6D 6C 2F 3E |
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| `<mime text/csv #"123,234,345">` | 83 74 6D 69 6D 65 78 74 65 78 74 2F 63 73 76 6B 31 32 33 2C 32 33 34 2C 33 34 35 |
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Applications making heavy use of `mime` records may choose to use a
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placeholder number for the symbol `mime` as well as the symbols for
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individual media types. For example, if placeholder number 1 were
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chosen for `mime`, and placeholder number 7 for `text/plain`, the
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second example above, `mime(text/plain #"ABC")`, would be encoded as
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second example above, `<mime text/plain #"ABC">`, would be encoded as
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`83 11 17 63 41 42 43`.
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### Unicode normalization forms.
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@ -1023,9 +1016,9 @@ A family of labels `i`*n* and `u`*n* for *n* ∈ {8,16,32,64} denote
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*n*-bit-wide signed and unsigned range restrictions, respectively.
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Records with these labels *MUST* have one field, a `SignedInteger`,
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which *MUST* fall within the appropriate range. That is, to be valid,
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- in `i8(`*x*`)`, -128 <= *x* <= 127.
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- in `u8(`*x*`)`, 0 <= *x* <= 255.
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- in `i16(`*x*`)`, -32768 <= *x* <= 32767.
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- in `<i8 `*x*`>`, -128 <= *x* <= 127.
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- in `<u8 `*x*`>`, 0 <= *x* <= 255.
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- in `<i16 `*x*`>`, -32768 <= *x* <= 32767.
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- etc.
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### Anonymous Tuples and Unit.
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@ -1033,15 +1026,15 @@ which *MUST* fall within the appropriate range. That is, to be valid,
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A `Tuple` is a `Record` with label `tuple` and zero or more fields,
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denoting an anonymous tuple of values.
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The 0-ary tuple, `tuple()`, denotes the empty tuple, sometimes called
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The 0-ary tuple, `<tuple>`, denotes the empty tuple, sometimes called
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"unit" or "void" (but *not* e.g. JavaScript's "undefined" value).
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### Null and Undefined.
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Tony Hoare's
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"[billion-dollar mistake](https://en.wikipedia.org/wiki/Tony_Hoare#Apologies_and_retractions)"
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can be represented with the 0-ary `Record` `null()`. An "undefined"
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value can be represented as `undefined()`.
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can be represented with the 0-ary `Record` `<null>`. An "undefined"
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value can be represented as `<undefined>`.
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### Dates and Times.
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@ -1429,14 +1422,6 @@ byte count acting as a kind of exponent underneath the sign bit.
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- Canonicalization and early-bailout-equivalence-checking are in
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tension with support for streaming values.
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Q. The postfix fields in the textual syntax come unannounced: "oh, and
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another thing, what you just read is a label, and here are some
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fields." This is a problem for interactive reading of textual syntax,
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because after a complete term, it needs to see the next character to
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tell whether it is an open-parenthesis or not! For this reason, I've
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disallowed whitespace between a label `Value` and the open-parenthesis
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of the fields. Is this reasonable??
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Q. To remain compatible with JSON, portions of the text syntax have to
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remain case-insensitive (`%i"..."`). However, non-JSON extensions do
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not. There's only one (?) at the moment, the `%i"f"` in `Float`;
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