Preserves Quick Reference

Tony Garnock-Jones tonyg@leastfixedpoint.com
September 2024. Version 0.996.0.

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 F1Fm>» = B4 «L» «F1» … «Fm» 84
«[X1Xm]» = B5 «X1» … «Xm» 84
«#{E1Em}» = B6 «E1» … «Em» 84
«{K1:V1Km: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)