((META (EMPTY-STRING title "Syntax of Symbolic Expressions") (WORD role "manual") (TAG-SET tags ("#manual" "#reference" "#zettelstore")) (WORD syntax "zmk") (ZID-SET back ("00001012051200" "00001012051400" "00001012053200" "00001012053300" "00001012053400" "00001012054200" "00001012921000" "00001012930000" "00001012931800")) (ZID-SET backward ("00001012051200" "00001012051400" "00001012053200" "00001012053300" "00001012053400" "00001012054200" "00001012921000" "00001012930000" "00001012931800")) (NUMBER box-number "1") (STRING copyright "(c) 2020-present by Detlef Stern <ds@zettelstore.de>") (TIMESTAMP created "20230403151127") (WORD lang "en") (EMPTY-STRING license "EUPL-1.2-or-later") (TIMESTAMP modified "20240413160345") (TIMESTAMP published "20240413160345") (WORD visibility "public")) (BLOCK (HEADING 1 () "syntax-of-lists" "syntax-of-lists" (TEXT "Syntax of lists")) (PARA (TEXT "A list always starts with the left parenthesis (") (FORMAT-QUOTE () (LITERAL-INPUT () "(")) (TEXT ", U+0028) and ends with a right parenthesis (") (FORMAT-QUOTE () (LITERAL-INPUT () ")")) (TEXT ", U+0029).") (SOFT) (TEXT "A list may contain a possibly empty sequence of elements, i.e. lists and / or atoms.")) (PARA (TEXT "Internally, lists are composed of ") (FORMAT-EMPH () (TEXT "cells")) (TEXT ".") (SOFT) (TEXT "A cell allows to store two values.") (SOFT) (TEXT "The first value references the first element of a list.") (SOFT) (TEXT "The second value references the rest of the list, or is the special value ") (FORMAT-EMPH () (TEXT "nil")) (TEXT " if there is no rest of the list.")) (PARA (TEXT "However, it is possible to store an atom as the second value of the last cell.") (SOFT) (TEXT "In this case, before the last element of a list of at least two elements, a full stop character (") (FORMAT-QUOTE () (LITERAL-INPUT () ".")) (TEXT ", U+002E) signals such a cell as the last two elements.") (SOFT) (TEXT "This allows a more space economic storage of data.")) (PARA (TEXT "A ") (FORMAT-EMPH () (TEXT "proper")) (TEXT " list, which contains ") (FORMAT-EMPH () (TEXT "nil")) (TEXT " as the second value of the last element might be pictured as follows:")) (BLOB () "svg" "<svg class=\"zs-draw\" width=\"400\" height=\"180\" version=\"1.1\" xmlns=\"http://www.w3.org/2000/svg\" xmlns:xlink=\"http://www.w3.org/1999/xlink\"><marker id=\"Pointer\" viewBox=\"0 0 10 10\" refX=\"5\" refY=\"5\" markerUnits=\"strokeWidth\" markerWidth=\"5\" markerHeight=\"10\" orient=\"auto\"><path d=\"M 0 0 L 10 5 L 0 10 z\" /></marker><g id=\"closed\" stroke=\"#000\" stroke-width=\"2\" fill=\"none\"><path id=\"closed1\" d=\"M 5 10 L 15 10 L 25 10 L 35 10 L 45 10 L 55 10 L 65 10 L 75 10 L 85 10 L 85 30 L 85 50 L 75 50 L 65 50 L 55 50 L 45 50 L 35 50 L 25 50 L 15 50 L 5 50 L 5 30 Z\" /><path id=\"closed5\" d=\"M 125 10 L 135 10 L 145 10 L 155 10 L 165 10 L 175 10 L 185 10 L 195 10 L 205 10 L 205 30 L 205 50 L 195 50 L 185 50 L 175 50 L 165 50 L 155 50 L 145 50 L 135 50 L 125 50 L 125 30 Z\" /><path id=\"closed8\" d=\"M 305 10 L 315 10 L 325 10 L 335 10 L 345 10 L 355 10 L 365 10 L 375 10 L 385 10 L 385 30 L 385 50 L 375 50 L 365 50 L 355 50 L 345 50 L 335 50 L 325 50 L 315 50 L 305 50 L 305 30 Z\" /><path id=\"closed12\" d=\"M 5 110 L 15 110 L 25 110 L 35 110 L 45 110 L 55 110 L 65 110 L 75 110 L 85 110 L 85 130 L 85 150 L 75 150 L 65 150 L 55 150 L 45 150 L 35 150 L 25 150 L 15 150 L 5 150 L 5 130 Z\" /><path id=\"closed13\" d=\"M 125 110 L 135 110 L 145 110 L 155 110 L 165 110 L 175 110 L 185 110 L 195 110 L 205 110 L 205 130 L 205 150 L 195 150 L 185 150 L 175 150 L 165 150 L 155 150 L 145 150 L 135 150 L 125 150 L 125 130 Z\" /><path id=\"closed14\" d=\"M 305 110 L 315 110 L 325 110 L 335 110 L 345 110 L 355 110 L 365 110 L 375 110 L 385 110 L 385 130 L 385 150 L 375 150 L 365 150 L 355 150 L 345 150 L 335 150 L 325 150 L 315 150 L 305 150 L 305 130 Z\" /></g><g id=\"lines\" stroke=\"#000\" stroke-width=\"2\" fill=\"none\"><path id=\"open0\" marker-end=\"url(#Pointer)\" d=\"M 5 10 L 15 10 L 25 10 L 35 10 L 45 10 L 55 10 L 65 10 L 75 10 L 85 10 L 85 30 L 95 30 L 105 30 L 115 30 \" /><path id=\"open2\" marker-end=\"url(#Pointer)\" d=\"M 5 10 L 15 10 L 25 10 L 35 10 L 45 10 L 55 10 L 65 10 L 75 10 L 85 10 L 85 30 L 85 50 L 75 50 L 65 50 L 55 50 L 45 50 L 35 50 L 25 50 L 25 70 L 25 90 \" /><path id=\"open3\" d=\"M 5 10 L 15 10 L 25 10 L 35 10 L 45 10 L 55 10 L 65 10 L 75 10 L 85 10 L 85 30 L 85 50 L 75 50 L 65 50 L 55 50 L 45 50 L 45 30 \" /><path id=\"open4\" marker-end=\"url(#Pointer)\" d=\"M 125 10 L 135 10 L 145 10 L 155 10 L 165 10 L 175 10 L 185 10 L 195 10 L 205 10 L 205 30 L 215 30 L 225 30 L 235 30 \" /><path id=\"open6\" marker-end=\"url(#Pointer)\" d=\"M 125 10 L 135 10 L 145 10 L 155 10 L 165 10 L 175 10 L 185 10 L 195 10 L 205 10 L 205 30 L 205 50 L 195 50 L 185 50 L 175 50 L 165 50 L 155 50 L 145 50 L 145 70 L 145 90 \" /><path id=\"open7\" d=\"M 125 10 L 135 10 L 145 10 L 155 10 L 165 10 L 175 10 L 185 10 L 195 10 L 205 10 L 205 30 L 205 50 L 195 50 L 185 50 L 175 50 L 165 50 L 165 30 \" /><path id=\"open9\" marker-end=\"url(#Pointer)\" d=\"M 305 10 L 315 10 L 325 10 L 335 10 L 345 10 L 355 10 L 365 10 L 375 10 L 385 10 L 385 30 L 385 50 L 375 50 L 365 50 L 355 50 L 345 50 L 335 50 L 325 50 L 325 70 L 325 90 \" /><path id=\"open10\" d=\"M 305 10 L 315 10 L 325 10 L 335 10 L 345 10 L 355 10 L 365 10 L 375 10 L 385 10 L 385 30 L 385 50 L 375 50 L 365 50 L 355 50 L 345 50 L 345 30 \" /><path id=\"open11\" marker-end=\"url(#Pointer)\" d=\"M 275 30 L 285 30 L 295 30 \" /></g><g id=\"text\" stroke=\"none\" style=\"font-family:monospace;font-size:15px\"><text id=\"obj15\" x=\"22.5\" y=\"35\">V</text><text id=\"obj16\" x=\"62.5\" y=\"35\">N</text><text id=\"obj17\" x=\"142.5\" y=\"35\">V</text><text id=\"obj18\" x=\"182.5\" y=\"35\">N</text><text id=\"obj19\" x=\"322.5\" y=\"35\">V</text><text id=\"obj20\" x=\"22.5\" y=\"135\">Elem1</text><text id=\"obj21\" x=\"142.5\" y=\"135\">Elem2</text><text id=\"obj22\" x=\"322.5\" y=\"135\">ElemN</text></g></svg>") (PARA (LITERAL-INPUT () "V") (TEXT " is a placeholder for a value, ") (LITERAL-INPUT () "N") (TEXT " is the reference to the next cell (also known as the rest / tail of the list).") (SOFT) (TEXT "Above list will be represented as an symbolic expression as ") (LITERAL-INPUT () "(Elem1 Elem2 ... ElemN)")) (PARA (TEXT "An improper list will have a non-") (FORMAT-EMPH () (TEXT "nil")) (TEXT " reference to an atom as the very last element")) (BLOB () "svg" "<svg class=\"zs-draw\" width=\"440\" height=\"180\" version=\"1.1\" xmlns=\"http://www.w3.org/2000/svg\" xmlns:xlink=\"http://www.w3.org/1999/xlink\"><marker id=\"Pointer\" viewBox=\"0 0 10 10\" refX=\"5\" refY=\"5\" markerUnits=\"strokeWidth\" markerWidth=\"5\" markerHeight=\"10\" orient=\"auto\"><path d=\"M 0 0 L 10 5 L 0 10 z\" /></marker><g id=\"closed\" stroke=\"#000\" stroke-width=\"2\" fill=\"none\"><path id=\"closed1\" d=\"M 5 10 L 15 10 L 25 10 L 35 10 L 45 10 L 55 10 L 65 10 L 75 10 L 85 10 L 85 30 L 85 50 L 75 50 L 65 50 L 55 50 L 45 50 L 35 50 L 25 50 L 15 50 L 5 50 L 5 30 Z\" /><path id=\"closed5\" d=\"M 125 10 L 135 10 L 145 10 L 155 10 L 165 10 L 175 10 L 185 10 L 195 10 L 205 10 L 205 30 L 205 50 L 195 50 L 185 50 L 175 50 L 165 50 L 155 50 L 145 50 L 135 50 L 125 50 L 125 30 Z\" /><path id=\"closed8\" d=\"M 305 10 L 315 10 L 325 10 L 335 10 L 345 10 L 355 10 L 365 10 L 375 10 L 385 10 L 385 30 L 385 50 L 375 50 L 365 50 L 355 50 L 345 50 L 335 50 L 325 50 L 315 50 L 305 50 L 305 30 Z\" /><path id=\"closed13\" d=\"M 5 110 L 15 110 L 25 110 L 35 110 L 45 110 L 55 110 L 65 110 L 75 110 L 85 110 L 85 130 L 85 150 L 75 150 L 65 150 L 55 150 L 45 150 L 35 150 L 25 150 L 15 150 L 5 150 L 5 130 Z\" /><path id=\"closed14\" d=\"M 125 110 L 135 110 L 145 110 L 155 110 L 165 110 L 175 110 L 185 110 L 195 110 L 205 110 L 205 130 L 205 150 L 195 150 L 185 150 L 175 150 L 165 150 L 155 150 L 145 150 L 135 150 L 125 150 L 125 130 Z\" /><path id=\"closed15\" d=\"M 255 110 L 265 110 L 275 110 L 285 110 L 295 110 L 305 110 L 315 110 L 325 110 L 335 110 L 335 130 L 335 150 L 325 150 L 315 150 L 305 150 L 295 150 L 285 150 L 275 150 L 265 150 L 255 150 L 255 130 Z\" /><path id=\"closed16\" d=\"M 355 110 L 365 110 L 375 110 L 385 110 L 395 110 L 405 110 L 415 110 L 425 110 L 425 130 L 425 150 L 415 150 L 405 150 L 395 150 L 385 150 L 375 150 L 365 150 L 355 150 L 355 130 Z\" /></g><g id=\"lines\" stroke=\"#000\" stroke-width=\"2\" fill=\"none\"><path id=\"open0\" marker-end=\"url(#Pointer)\" d=\"M 5 10 L 15 10 L 25 10 L 35 10 L 45 10 L 55 10 L 65 10 L 75 10 L 85 10 L 85 30 L 95 30 L 105 30 L 115 30 \" /><path id=\"open2\" marker-end=\"url(#Pointer)\" d=\"M 5 10 L 15 10 L 25 10 L 35 10 L 45 10 L 55 10 L 65 10 L 75 10 L 85 10 L 85 30 L 85 50 L 75 50 L 65 50 L 55 50 L 45 50 L 35 50 L 25 50 L 25 70 L 25 90 \" /><path id=\"open3\" d=\"M 5 10 L 15 10 L 25 10 L 35 10 L 45 10 L 55 10 L 65 10 L 75 10 L 85 10 L 85 30 L 85 50 L 75 50 L 65 50 L 55 50 L 45 50 L 45 30 \" /><path id=\"open4\" marker-end=\"url(#Pointer)\" d=\"M 125 10 L 135 10 L 145 10 L 155 10 L 165 10 L 175 10 L 185 10 L 195 10 L 205 10 L 205 30 L 215 30 L 225 30 L 235 30 \" /><path id=\"open6\" marker-end=\"url(#Pointer)\" d=\"M 125 10 L 135 10 L 145 10 L 155 10 L 165 10 L 175 10 L 185 10 L 195 10 L 205 10 L 205 30 L 205 50 L 195 50 L 185 50 L 175 50 L 165 50 L 155 50 L 145 50 L 145 70 L 145 90 \" /><path id=\"open7\" d=\"M 125 10 L 135 10 L 145 10 L 155 10 L 165 10 L 175 10 L 185 10 L 195 10 L 205 10 L 205 30 L 205 50 L 195 50 L 185 50 L 175 50 L 165 50 L 165 30 \" /><path id=\"open9\" marker-end=\"url(#Pointer)\" d=\"M 305 10 L 315 10 L 325 10 L 335 10 L 345 10 L 355 10 L 365 10 L 375 10 L 385 10 L 385 30 L 385 50 L 375 50 L 365 50 L 355 50 L 345 50 L 335 50 L 325 50 L 325 70 L 325 90 \" /><path id=\"open10\" d=\"M 305 10 L 315 10 L 325 10 L 335 10 L 345 10 L 355 10 L 365 10 L 375 10 L 385 10 L 385 30 L 385 50 L 375 50 L 365 50 L 355 50 L 345 50 L 345 30 \" /><path id=\"open11\" marker-end=\"url(#Pointer)\" d=\"M 305 10 L 315 10 L 325 10 L 335 10 L 345 10 L 355 10 L 365 10 L 375 10 L 385 10 L 385 30 L 385 50 L 375 50 L 365 50 L 365 70 L 365 90 \" /><path id=\"open12\" marker-end=\"url(#Pointer)\" d=\"M 275 30 L 285 30 L 295 30 \" /></g><g id=\"text\" stroke=\"none\" style=\"font-family:monospace;font-size:15px\"><text id=\"obj17\" x=\"22.5\" y=\"35\">V</text><text id=\"obj18\" x=\"62.5\" y=\"35\">N</text><text id=\"obj19\" x=\"142.5\" y=\"35\">V</text><text id=\"obj20\" x=\"182.5\" y=\"35\">N</text><text id=\"obj21\" x=\"322.5\" y=\"35\">V</text><text id=\"obj22\" x=\"362.5\" y=\"35\">V</text><text id=\"obj23\" x=\"22.5\" y=\"135\">Elem1</text><text id=\"obj24\" x=\"142.5\" y=\"135\">Elem2</text><text id=\"obj25\" x=\"272.5\" y=\"135\">ElemN</text><text id=\"obj26\" x=\"372.5\" y=\"135\">Atom</text></g></svg>") (PARA (TEXT "Above improper list will be represented as an symbolic expression as ") (LITERAL-INPUT () "(Elem1 Elem2 ... ElemN . Atom)")) (HEADING 1 () "syntax-of-numbers-atom" "syntax-of-numbers-atom" (TEXT "Syntax of numbers (atom)")) (PARA (TEXT "A number is a non-empty sequence of digits (") (FORMAT-QUOTE () (TEXT "0")) (TEXT " ... ") (FORMAT-QUOTE () (TEXT "9")) (TEXT ").") (SOFT) (TEXT "The smallest number is ") (LITERAL-CODE () "0") (TEXT ", there are no negative numbers.")) (HEADING 1 () "syntax-of-symbols-atom" "syntax-of-symbols-atom" (TEXT "Syntax of symbols (atom)")) (PARA (TEXT "A symbol is a non-empty sequence of printable characters, except left or right parenthesis.") (SOFT) (TEXT "Unicode characters of the following categories contains printable characters in the above sense: letter (L), number (N), punctuation (P), symbol (S).") (SOFT) (TEXT "Symbols are case-sensitive, i.e. ") (FORMAT-QUOTE () (LITERAL-INPUT () "ZETTEL")) (TEXT " and ") (FORMAT-QUOTE () (LITERAL-INPUT () "zettel")) (TEXT " denote different symbols.")) (HEADING 1 () "syntax-of-string-atom" "syntax-of-string-atom" (TEXT "Syntax of string (atom)")) (PARA (TEXT "A string starts with a quotation mark (") (FORMAT-QUOTE () (LITERAL-INPUT () "\"")) (TEXT ", U+0022), contains a possibly empty sequence of Unicode characters, and ends with a quotation mark.") (SOFT) (TEXT "To allow a string to contain a quotations mark, it must be prefixed by one backslash (") (FORMAT-QUOTE () (LITERAL-INPUT () "\\")) (TEXT ", U+005C).") (SOFT) (TEXT "To allow a string to contain a backslash, it also must be prefixed by one backslash.") (SOFT) (TEXT "Unicode characters with a code less than U+FF are encoded by by the sequence ") (FORMAT-QUOTE () (LITERAL-INPUT () "\\xNM")) (TEXT ", where ") (LITERAL-INPUT () "NM") (TEXT " is the hex encoding of the character.") (SOFT) (TEXT "Unicode characters with a code less than U+FFFF are encoded by by the sequence ") (FORMAT-QUOTE () (LITERAL-INPUT () "\\uNMOP")) (TEXT ", where ") (LITERAL-INPUT () "NMOP") (TEXT " is the hex encoding of the character.") (SOFT) (TEXT "Unicode characters with a code less than U+FFFFFF are encoded by by the sequence ") (FORMAT-QUOTE () (LITERAL-INPUT () "\\UNMOPQR")) (TEXT ", where ") (LITERAL-INPUT () "NMOPQR") (TEXT " is the hex encoding of the character.") (SOFT) (TEXT "In addition, the sequence ") (FORMAT-QUOTE () (LITERAL-INPUT () "\\t")) (TEXT " encodes a horizontal tab (U+0009), the sequence ") (FORMAT-QUOTE () (LITERAL-INPUT () "\\n")) (TEXT " encodes a line feed (U+000A).")) (HEADING 1 () "see-also" "see-also" (TEXT "See also")) (UNORDERED (BLOCK (PARA (TEXT "Currently, Zettelstore uses ") (LINK-EXTERNAL () "https://t73f.de/r/sx" (TEXT "Sx")) (TEXT " (") (FORMAT-QUOTE () (TEXT "Symbolic eXpression framework")) (TEXT ") to implement symbolic expressions.") (SOFT) (TEXT "The project page might contain additional information about the full syntax.")) (PARA (TEXT "Zettelstore only uses lists, numbers, string, and symbols to represent zettel."))))))