Start adding regexp support to language

Starts #130.
Also part of #1125, #1132, #1130.

lang/check-grammar.sh

@@ -24,7 +24,7 @@ sed -e 's/<abbr>/\n<abbr>/g' $b/grammar.xml \
 join -a 2 -v 2 $b/defs.txt $b/used.txt >$b/undef.txt
 test -s $b/undef.txt && echo Undefined references found: `cat $b/undef.txt` 1>&2
 join -a 1 -v 1 $b/defs.txt $b/used.txt \
-     | grep -v '^TokenWhiteSpace\|module-part$' >$b/unused.txt
+     | grep -v '^TokenWhiteSpace\|module-part\|RegExp$' >$b/unused.txt
 test -s $b/unused.txt && echo Unused definitions found: `cat $b/unused.txt` 1>&2
 exit 0
 

lang/lib/regexp.bal

@@ -0,0 +1,54 @@
+// Copyright (c) 2022 WSO2 Inc. (http://www.wso2.org) All Rights Reserved.
+//
+// WSO2 Inc. licenses this file to you under the Apache License,
+// Version 2.0 (the "License"); you may not use this file except
+// in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+# The type RegExp refers to the tagged data basic type with tag `re`.
+@builtinSubtype
+public type RegExp any;
+
+public type Span readonly & object {
+   public int startIndex;
+   public int endIndex;
+   // This avoids constructtng a potentially long string unless and until it is needed
+   isolated function substring() returns string;
+};
+
+public type Groups readonly & [Span, Span?...];
+
+# Returns the span of the first match that starts at or after startIndex.
+public isolated function find(RegExp re, string str, int startIndex = 0) returns Span? = external;
+
+public isolated function findGroups(RegExp re, string str, int startIndex = 0) returns Groups? = external;
+
+# Return all non-overlapping matches
+public isolated function findAll(RegExp re, string str, int startIndex = 0) returns Span[] = external;
+public isolated function findAllGroups(RegExp re, string str, int startIndex = 0) returns Groups[] = external;
+
+public isolated function matchAt(RegExp re, string str, int startIndex = 0) returns Span? = external;
+public isolated function matchGroupsAt(RegExp re, string str, int startIndex = 0) returns Groups? = external;
+
+# Says whether there is a match of the RegExp that starts at the beginning of the string and ends at the end of the string.
+public isolated function isFullMatch(RegExp re, string str) returns boolean = external;
+public isolated function fullMatchGroups(RegExp re, string str) returns Groups? = external;
+
+public type ReplacerFunction function(Groups groups) returns string;
+public type Replacement ReplacerFunction|string;
+
+# Replaces the first occurrence of a regular expression.
+public isolated function replace(RegExp re, string str, @isolatedParam Replacement replacement, int startIndex = 0) returns string = external;
+# Replaces all occurrences of a regular expression.
+public isolated function replaceAll(RegExp re, string str, @isolatedParam Replacement replacement, int startIndex = 0) returns string = external;
+
+public isolated function fromString(string str) returns RegExp|error = external;