Regular expression patterns
++(New since 7 January 2006.) +
++To define string operations computed at compile time, such +as in morphology, it is handy to use regular expression patterns: +
+-
+
- p
+q : token consisting of p followed by q + - p
*: token p repeated 0 or more times + (max the length of the string to be matched) + -p : matches anything that p does not match +- x
@p : bind to x what p matches + - p
|q : matches what either p or q matches +
+The last three apply to all types of patterns, the first two only to token strings. +Example: plural formation in Swedish 2nd declension +(pojke-pojkar, nyckel-nycklar, seger-segrar, bil-bilar): +
+
+ plural2 : Str -> Str = \w -> case w of {
+ pojk + "e" => pojk + "ar" ;
+ nyck + "e" + l@("l" | "r" | "n") => nyck + l + "ar" ;
+ bil => bil + "ar"
+ } ;
+
++Another example: English noun plural formation. +
+
+ plural : Str -> Str = \w -> case w of {
+ _ + ("s" | "z" | "x" | "sh") => w + "es" ;
+ _ + ("a" | "o" | "u" | "e") + "y" => w + "s" ;
+ x + "y" => x + "ies" ;
+ _ => w + "s"
+ } ;
+
+
+
+Semantics: variables are always bound to the first match, which is the first
+in the sequence of binding lists Match p v defined as follows. In the definition,
+p is a pattern and v is a value.
+
+ Match (p1|p2) v = Match p1 v ++ Match p2 v + Match (p1+p2) s = [Match p1 s1 ++ Match p2 s2 | i <- [0..length s], (s1,s2) = splitAt i s] + Match p* s = Match "" s ++ Match p s ++ Match (p + p) s ++ ... + Match c v = [[]] if c == v -- for constant and literal patterns c + Match x v = [[(x,v)]] -- for variable patterns x + Match x@p v = [[(x,v)]] + M if M = Match p v /= [] + Match p v = [] otherwise -- failure ++
+Examples: +
+-
+
x + "e" + ymatches"peter"withx = "p", y = "ter"+x@("foo"*)matches any token withx = ""+x + y@("er"*)matches"burgerer"withx = "burg", y = "erer"+
Prefix-dependent choices
The construct exemplified in @@ -2064,7 +2130,7 @@ This very example does not work in all situations: the prefix } ;
- +Predefined types and operations
GF has the following predefined categories in abstract syntax: @@ -2087,11 +2153,11 @@ they can be used as arguments. For example: -- e.g. (StreetAddress 10 "Downing Street") : Address
- -More features of the module system
-Interfaces, instances, and functors
+More features of the module system
+Interfaces, instances, and functors
+Resource grammars and their reuse
A resource grammar is a grammar built on linguistic grounds, @@ -2144,19 +2210,19 @@ The rest of the modules (black) come from the resource.
Restricted inheritance and qualified opening
-More concepts of abstract syntax
+Restricted inheritance and qualified opening
-Dependent types
+More concepts of abstract syntax
-Higher-order abstract syntax
+Dependent types
-Semantic definitions
+Higher-order abstract syntax
-List categories
+Semantic definitions
+List categories
+Transfer modules
Transfer means noncompositional tree-transforming operations. @@ -2175,9 +2241,9 @@ See the transfer language documentation for more information.
- -Practical issues
+Practical issues
+Lexers and unlexers
Lexers and unlexers can be chosen from
@@ -2213,7 +2279,7 @@ Given by help -lexer, help -unlexer:
Efficiency of grammars
Issues: @@ -2224,7 +2290,7 @@ Issues:
