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| -rw-r--r-- | txr.1 | 208 |
1 files changed, 202 insertions, 6 deletions
@@ -191,8 +191,19 @@ . shift . \} . el \{\ -. as s \\$1 -. shift +. ie "\\$1"<2>" \{\ +. shift +. as s \\$1\fI<\\$2>\fP\\$3\fI<\\$4>\fP\\$5 +. shift +. shift +. shift +. shift +. shift +. \} +. el \{\ +. as s \\$1 +. shift +. \} . \} . \} . \} @@ -233,16 +244,27 @@ . shift . \} . el \{\ -. ie "\\$1"><" \{\ +. ie "\\$1"<2>" \{\ +. shift +. as s \\$1\\f5\\$2\\f4\\$3\\f5\\$4\\f4\\$5 +. shift . shift -. as s \\f5\\$1\\f4\\$2\f5\\$3\\f4 . shift . shift . shift . \} . el \{\ -. as s \\$1 -. shift +. ie "\\$1"><" \{\ +. shift +. as s \\f5\\$1\\f4\\$2\f5\\$3\\f4 +. shift +. shift +. shift +. \} +. el \{\ +. as s \\$1 +. shift +. \} . \} . \} . \} @@ -40547,6 +40569,180 @@ that being a syntactic sugar for .brev +.NP* Quasiliteral match +.synb +.mets <> "`...@" var "...`" +.syne +.desc +The quasiliteral syntax is supported as a pattern matching operator. +The corresponding object is required to be a character string, which +is analyzed according to the structure of the quasiliteral pattern, +and portions of the string are captured by variables. If the corresponding +object isn't a string according to +.code stringp +then the match fails. The quasiliteral pattern must match the entire +input string. + +Note: this feature is new, having been introduced in \*(TX 258, +and should be regarded as being in "beta" state, with requirements +that have not been finalized. This notice will be removed when +that is no longer the case. + +A quasiliteral pattern matches in a linear fashion, from left to right. +Variables bound earlier in the pattern can be referenced later in the pattern +as bound variables. + +Bound variables denote character strings in accordance with the usual +quasiliteral conversion and formatting rules. All of the modifier notations may +be used. For instance, if +.code x +is a bound variable, then +.code "@{x -40}" +denotes the value of +.code x +converted to a string, and right-aligned in a forty-character-wide field. +Consequently, the notation matches exactly such a forty-character text. + +In the following description of the quasiliteral pattern matching rules, the +symbols +.metn uv , +.meta uv0 +and +.meta uv1 +represent to unbound variables: variables which have no apparent +lexical binding and are not defined as global variables. Unless indicated +otherwise, +.mono +.meti >> @ uv +.onom +refers to a plain variable syntax such as +.code @abc +or else to braced syntax without modifiers, such as +.codn @{abc} . +The same remarks apply to +.meta uv0 +and +.metn uv1 . +The symbol +.meta bv +represents an unbound variables: a variable which has an existing binding, +which can occur in the form of the ordinary notation, or the braced notation +with or without modifiers. +The notation +.codn {P} , +.codn {P0} , +.codn {P1} ... +denotes a substring of the pattern, possibly empty. + +.RS +.coIP `` +The empty quasiliteral pattern matches an empty string. +.coIP `text{P}` +A quasiliteral pattern which begins with a portion of text matches a string +which begins with the same text. The remaining portion +.code {P} +of the pattern is then matched against a suffix of the input string which +excludes the matched text. +.meIP <> `@ uv ` +A simple unbound variable occurring as the last element of the pattern +matches and binds the entire rest of the input string. +.meIP <> `@ uv text{P}` +A simple unbound variable followed by a text element matches the input string if +.str text +occurs in that string as a substring. In that case, +.meta uv +is bound to the possibly empty prefix of the input string consisting of the +characters before the leftmost match for +.strn text . +The rest of the pattern +.code {P} +is then matched against that suffix of the input string which begins after the +last character of the leftmost match for +.strn text . +.meIP <2> `@ uv @ bv {P}` +The bound variable +.meta bv +is converted to text in the manner of an ordinary quasiliteral substitution. +The situation then reduces to the +.mono +.meti <> `@ uv text{P}` +.onom +pattern, where +.code text +denotes the character string produced by substitution of +.metn bv . +.meIP >> `@{ uv << integer }{P}` +An unbound variable +.meta uv +which uses the brace notation to specify a literal +.meta integer +modifier denotes +a match for that many characters. It is an error if the value is zero or +negative. The match succeeds if the input string has at least that +many characters, in which case the variable +.meta uv +takes on those characters, and the rest of the pattern is matched against +a suffix of the string with those characters removed. +.meIP >> `@{ uv <> #/ regex /}{P}` +An unbound variable +.meta uv +which carries a regular expression modifier specifies a regular expression +match. If a prefix of the input string matches +.metn regex , +then the match is successful and +.meta uv +captures that prefix. The rest of the pattern +.code {P} +is then matched against the rest of the string after the prefix. +.mono +.meti >> @ bv {R} +.onom +The bound variable +.meta bv +is converted to text the manner of an ordinary quasiliteral substitution. +The situation then reduces to the +.code `text{P}` +pattern, where +.code text +denotes the character string produced by substitution of +.metn bv . +.meIP <2> `@ uv0 @ uv1 {P0}` +Two consecutive unbound variables, where +.meta uv0 +is a plain variable with no modifiers, constitutes an invalid pattern. +This situation is diagnosed as an error. If +.meta uv0 +is braced, carrying an integer or regular expression modifier +.metn mod , +then the situation is treated as the pattern +.mono +.meti >> `@{ uv << mod }{P}` +.onom +where +.code {P} +refers to the +.mono +.meti <> @ uv1 {P0} +.onom +portion. +.RE +.IP +No other quasiliteral syntax, or combination of variable modifiers, is +supported in quasiliteral patterns. + +.TP* Examples: + +.verb + (when-match `@a-@b` "foo-bar" (list a b)) -> ("foo" "bar") + + (when-match `@{a #/\ed+/}@b` "123xy" (list a b)) -> ("123" "xy") + + (let ((a 42)) + (when-match `[@{a -8}] @b` "[ 42] packets` b)) + -> "packets" + +.brev + .coNP Pattern operator @ struct .synb .mets @(struct < name >> { slot-name << pattern }*) |