((h2 (@ (id . "syntax-of-lists")) "Syntax of lists") (p "A list always starts with the left parenthesis (" (@L (@H "&ldquo;") (kbd "(") (@H "&rdquo;")) ", U+0028) and ends with a right parenthesis (" (@L (@H "&ldquo;") (kbd ")") (@H "&rdquo;")) ", U+0029)." " " "A list may contain a possibly empty sequence of elements, i.e. lists and / or atoms.") (p "Internally, lists are composed of " (em "cells") "." " " "A cell allows to store two values." " " "The first value references the first element of a list." " " "The second value references the rest of the list, or is the special value " (em "nil") " if there is no rest of the list.") (p "However, it is possible to store an atom as the second value of the last cell." " " "In this case, before the last element of a list of at least two elements, a full stop character (" (@L (@H "&ldquo;") (kbd ".") (@H "&rdquo;")) ", U+002E) signals such a cell as the last two elements." " " "This allows a more space economic storage of data.") (p "A " (em "proper") " list, which contains " (em "nil") " as the second value of the last element might be pictured as follows:") (p (@H "<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>")) (p (kbd "V") " is a placeholder for a value, " (kbd "N") " is the reference to the next cell (also known as the rest / tail of the list)." " " "Above list will be represented as an symbolic expression as " (kbd "(Elem1 Elem2 ... ElemN)")) (p "An improper list will have a non-" (em "nil") " reference to an atom as the very last element") (p (@H "<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>")) (p "Above improper list will be represented as an symbolic expression as " (kbd "(Elem1 Elem2 ... ElemN . Atom)")) (h2 (@ (id . "syntax-of-numbers-atom")) "Syntax of numbers (atom)") (p "A number is a non-empty sequence of digits (" (@L (@H "&ldquo;") "0" (@H "&rdquo;")) " ... " (@L (@H "&ldquo;") "9" (@H "&rdquo;")) ")." " " "The smallest number is " (code "0") ", there are no negative numbers.") (h2 (@ (id . "syntax-of-symbols-atom")) "Syntax of symbols (atom)") (p "A symbol is a non-empty sequence of printable characters, except left or right parenthesis." " " "Unicode characters of the following categories contains printable characters in the above sense: letter (L), number (N), punctuation (P), symbol (S)." " " "Symbols are case-sensitive, i.e. " (@L (@H "&ldquo;") (kbd "ZETTEL") (@H "&rdquo;")) " and " (@L (@H "&ldquo;") (kbd "zettel") (@H "&rdquo;")) " denote different symbols.") (h2 (@ (id . "syntax-of-string-atom")) "Syntax of string (atom)") (p "A string starts with a quotation mark (" (@L (@H "&ldquo;") (kbd "\"") (@H "&rdquo;")) ", U+0022), contains a possibly empty sequence of Unicode characters, and ends with a quotation mark." " " "To allow a string to contain a quotations mark, it must be prefixed by one backslash (" (@L (@H "&ldquo;") (kbd "\\") (@H "&rdquo;")) ", U+005C)." " " "To allow a string to contain a backslash, it also must be prefixed by one backslash." " " "Unicode characters with a code less than U+FF are encoded by by the sequence " (@L (@H "&ldquo;") (kbd "\\xNM") (@H "&rdquo;")) ", where " (kbd "NM") " is the hex encoding of the character." " " "Unicode characters with a code less than U+FFFF are encoded by by the sequence " (@L (@H "&ldquo;") (kbd "\\uNMOP") (@H "&rdquo;")) ", where " (kbd "NMOP") " is the hex encoding of the character." " " "Unicode characters with a code less than U+FFFFFF are encoded by by the sequence " (@L (@H "&ldquo;") (kbd "\\UNMOPQR") (@H "&rdquo;")) ", where " (kbd "NMOPQR") " is the hex encoding of the character." " " "In addition, the sequence " (@L (@H "&ldquo;") (kbd "\\t") (@H "&rdquo;")) " encodes a horizontal tab (U+0009), the sequence " (@L (@H "&ldquo;") (kbd "\\n") (@H "&rdquo;")) " encodes a line feed (U+000A).") (h2 (@ (id . "see-also")) "See also") (ul (li (p "Currently, Zettelstore uses " (a (@ (href . "https://t73f.de/r/sx") (rel . "external")) "Sx") " (" (@L (@H "&ldquo;") "Symbolic eXpression framework" (@H "&rdquo;")) ") to implement symbolic expressions." " " "The project page might contain additional information about the full syntax.") (p "Zettelstore only uses lists, numbers, string, and symbols to represent zettel."))))