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| -rw-r--r-- | lib/pure/strscans.nim | 143 |
1 files changed, 142 insertions, 1 deletions
diff --git a/lib/pure/strscans.nim b/lib/pure/strscans.nim index fc400173f..83b86fd54 100644 --- a/lib/pure/strscans.nim +++ b/lib/pure/strscans.nim @@ -62,7 +62,7 @@ Startswith vs full match ======================== ``scanf`` returns true if the input string **starts with** the specified -pattern. If instead it should only return true if theres is also nothing +pattern. If instead it should only return true if there is also nothing left in the input, append ``$.`` to your pattern. @@ -112,6 +112,147 @@ It also possible to pass arguments to a user definable matcher: if scanf("2013-01-03", "${ndigits(4)}-${ndigits(2)}-${ndigits(2)}$.", year, month, day): ... + +The scanp macro +=============== + +This module also implements a ``scanp`` macro, which syntax somewhat resembles +an EBNF or PEG grammar, except that it uses Nim's expression syntax and so has +to use prefix instead of postfix operators. + +============== =============================================================== +``(E)`` Grouping +``*E`` Zero or more +``+E`` One or more +``?E`` Zero or One +``E{n,m}`` From ``n`` up to ``m`` times ``E`` +``~Ε`` Not predicate +``a ^* b`` Shortcut for ``?(a *(b a))``. Usually used for separators. +``a ^* b`` Shortcut for ``?(a +(b a))``. Usually used for separators. +``'a'`` Matches a single character +``{'a'..'b'}`` Matches a character set +``"s"`` Matches a string +``E -> a`` Bind matching to some action +``$_`` Access the currently matched character +============== =============================================================== + +Note that unordered or ordered choice operators (``/``, ``|``) are +not implemented. + +Simple example that parses the ``/etc/passwd`` file line by line: + +.. code-block:: nim + + const + etc_passwd = """root:x:0:0:root:/root:/bin/bash + daemon:x:1:1:daemon:/usr/sbin:/bin/sh + bin:x:2:2:bin:/bin:/bin/sh + sys:x:3:3:sys:/dev:/bin/sh + nobody:x:65534:65534:nobody:/nonexistent:/bin/sh + messagebus:x:103:107::/var/run/dbus:/bin/false + """ + + proc parsePasswd(content: string): seq[string] = + result = @[] + var idx = 0 + while true: + var entry = "" + if scanp(content, idx, +(~{'\L', '\0'} -> entry.add($_)), '\L'): + result.add entry + else: + break + +The ``scanp`` maps the grammar code into Nim code that performs the parsing. +The parsing is performed with the help of 3 helper templates that that can be +implemented for a custom type. + +These templates need to be named ``atom`` and ``nxt``. ``atom`` should be +overloaded to handle both single characters and sets of character. + +.. code-block:: nim + + import streams + + template atom(input: Stream; idx: int; c: char): bool = + ## Used in scanp for the matching of atoms (usually chars). + peekChar(input) == c + + template atom(input: Stream; idx: int; s: set[char]): bool = + peekChar(input) in s + + template nxt(input: Stream; idx, step: int = 1) = + inc(idx, step) + setPosition(input, idx) + + if scanp(content, idx, +( ~{'\L', '\0'} -> entry.add(peekChar($input))), '\L'): + result.add entry + + +Calling ordinary Nim procs inside the macro is possible: + +.. code-block:: nim + + proc digits(s: string; intVal: var int; start: int): int = + var x = 0 + while result+start < s.len and s[result+start] in {'0'..'9'} and s[result+start] != ':': + x = x * 10 + s[result+start].ord - '0'.ord + inc result + intVal = x + + proc extractUsers(content: string): seq[string] = + # Extracts the username and home directory + # of each entry (with UID greater than 1000) + const + digits = {'0'..'9'} + result = @[] + var idx = 0 + while true: + var login = "" + var uid = 0 + var homedir = "" + if scanp(content, idx, *(~ {':', '\0'}) -> login.add($_), ':', * ~ ':', ':', + digits($input, uid, $index), ':', *`digits`, ':', * ~ ':', ':', + *('/', * ~{':', '/'}) -> homedir.add($_), ':', *('/', * ~{'\L', '/'}), '\L'): + if uid >= 1000: + result.add login & " " & homedir + else: + break + +When used for matching, keep in mind that likewise scanf, no backtracking +is performed. + +.. code-block:: nim + + proc skipUntil(s: string; until: string; unless = '\0'; start: int): int = + # Skips all characters until the string `until` is found. Returns 0 + # if the char `unless` is found first or the end is reached. + var i = start + var u = 0 + while true: + if s[i] == '\0' or s[i] == unless: + return 0 + elif s[i] == until[0]: + u = 1 + while i+u < s.len and u < until.len and s[i+u] == until[u]: + inc u + if u >= until.len: break + inc(i) + result = i+u-start + + iterator collectLinks(s: string): string = + const quote = {'\'', '"'} + var idx, old = 0 + var res = "" + while idx < s.len: + old = idx + if scanp(s, idx, "<a", skipUntil($input, "href=", '>', $index), + `quote`, *( ~`quote`) -> res.add($_)): + yield res + res = "" + idx = old + 1 + + for r in collectLinks(body): + echo r ]## |