Preserves Quick Reference
Tony Garnock-Jones tonyg@leastfixedpoint.com
February 2025. Version 0.996.2.
These are non-normative “reference card” definitions. See also the normative semantics, text syntax specification, and machine-oriented syntax specification, and the experimental P-expressions definition.
Machine-Oriented Binary Syntax
For a value V, we write «V» for the binary encoding of V.
«#f» |
= | 80 |
«#t» |
= | 81 |
«@W V» |
= | 85 «W» «V» |
«#:V» |
= | 86 «V» |
| «V» | = | 8708 binary64(V) |
if V ∈ Double |
| «V» | = | B0 varint(|intbytes(V)|) intbytes(V) |
if V ∈ SignedInteger |
| «V» | = | B1 varint(|utf8(V)|) utf8(V) |
if V ∈ String |
| «V» | = | B2 varint(|V|) V |
if V ∈ ByteString |
| «V» | = | B3 varint(|utf8(V)|) utf8(V) |
if V ∈ Symbol |
«<L F1 … Fm>» |
= | B4 «L» «F1» … «Fm» 84 |
«[X1 … Xm]» |
= | B5 «X1» … «Xm» 84 |
«#{E1 … Em}» |
= | B6 «E1» … «Em» 84 |
«{K1:V1 … Km:Vm}» |
= | B7 «K1» «V1» … «Km» «Vm» 84 |
| varint(n) | = | n | if n < 128 |
| (n & 127) | 128 varint(n >> 7) | if n ≥ 128 |
| intbytes(n) | = | the empty sequence if n = 0, otherwise signedBigEndian(n) |
| signedBigEndian(n) | = | n & 255 | if −128 ≤ n ≤ 127 |
| signedBigEndian(n >> 8) n & 255 | otherwise |
The function binary64(D) yields the big-endian 8-byte IEEE 754 binary representation of D.
Human-Oriented Text Syntax
| Document | := | Value ws |
| Value | := | ws (Record | Collection | Embedded | Annotated | Atom) |
| Collection | := | Sequence | Dictionary | Set |
| Record | := | <Value+ ws> |
| Sequence | := | [(commas Value)⋆ commas] |
| Set | := | #{(commas Value)⋆ commas} |
| Dictionary | := | { (commas Value ws:Value)⋆ commas} |
| commas | := | (ws ,)⋆ ws |
| Embedded | := | #:Value |
| Annotated | := | Annotation Value |
| Annotation | := | @Value |# ((space | tab | !) linecomment) (cr | lf) |
| Atom | := | Boolean | ByteString | String | QuotedSymbol | Symbol | Number |
| Boolean | := | #t|#f |
| ByteString | := | #"binchar⋆ "|#x" (ws hex hex)⋆ ws"|#[ (ws base64char)⋆ ws] |
| String | := | " (« any unicode scalar value except \ or " » | escaped |\")⋆ " |
| QuotedSymbol | := | ' (« any unicode scalar value except \ or ' » | escaped |\')⋆ ' |
| Symbol | := | (A..Z|a..z|0..9| sympunct | symuchar)+ |
| Number | := | Double | SignedInteger |
| Double | := | flt |#xd" (ws hex hex)8 ws" |
| SignedInteger | := | int |
| escaped | := | \\|\/|\b|\f|\n|\r|\t|\uhex hex hex hex |
| binescaped | := | \\|\/|\b|\f|\n|\r|\t|\xhex hex |
| binchar | := | « any unicode scalar value ≥32 and ≤126, except \ or " » | binescaped |\" |
| base64char | := | A..Z|a..z|0..9|+|/|-|_|= |
| sympunct | := | ~|!|$|%|^|&|*|?|_|=|+|-|/|.|| |
| symuchar | := | « any scalar value ≥128 whose Unicode category is Lu, Ll, Lt, Lm, Lo, Mn, Mc, Me, Nd, Nl, No, Pc, Pd, Po, Sc, Sm, Sk, So, or Co » |
| flt | := | int ( frac exp | frac | exp ) |
| int | := | (-|+) (0..9)+ |
| frac | := | . (0..9)+ |
| exp | := | (e|E) (-|+) (0..9)+ |
| hex | := | A..F|a..f|0..9 |
| ws | := | (space | tab | cr | lf)⋆ |
| delimiter | := | ws | < | > | [ | ] | { | } | # | : | " | ' | @ | ; | , |
| linecomment | := | « any unicode scalar value except cr or lf »⋆ |
P-expression Syntax
The definitions of Atom, ws, and linecomment are as given in the Preserves text syntax.
| Document | := | Expr⋆ Trailer ws |
| Expr | := | ws (SimpleExpr | Punct) |
| SimpleExpr | := | Compound | Embedded | Annotated | Atom |
| Compound | := | Sequence | Record | Block | Group | Set |
| Punct | := | , | ; | :+ |
| Sequence | := | [ Expr⋆ Trailer ws ] |
| Record | := | < Expr⋆ Trailer ws > |
| Block | := | { Expr⋆ Trailer ws } |
| Group | := | ( Expr⋆ Trailer ws ) |
| Set | := | #{ Expr⋆ Trailer ws } |
| Trailer | := | (ws Annotation)⋆ |
| Embedded | := | #: SimpleExpr |
| Annotated | := | Annotation SimpleExpr |
| Annotation | := | @ SimpleExpr | # ((space | tab | !) linecomment) (cr | lf) |