Character Pattern Functions

Constructs a pattern that immediately stops the pattern match. The matcher does not back up and retry any alternatives. Conditional assignments are not made. Immediate assignments that were already made are kept.

0 when a match is stopped.

Pat Altern(pattern1, <pattern 2, ...>)

none

Constructs a pattern that matches any one of the pattern arguments.

A pattern.

One or more patterns.

Pat Any("string")

Constructs a pattern that matches a single character in the argument.

Constructs a pattern that matches an arbitrary string. It initially matches the null string. It then matches one additional character each time the pattern matcher backs into it.

p = "the beginning" + Pat Arb() >? stuffInTheMiddle + "the end";

Pat Match( "in the beginning of the story, and not near the end, there are three bears", p );

Show( stuffInTheMiddle );

stuffInTheMiddle = " of the story, and not near "

Pat Arb No(pattern)

Constructs a pattern that matches zero or more copies of pattern.

adjectives = "large" | "medium" | "small" | "warm" | "cold" | "hot" | "sweet";

rc = Pat Match( "I would like a medium hot, sweet tea please",

               Pat Arbno( adjectives | Pat Any(", ") ) >> adj +

               ("tea" | "coffee" | "milk") );

Show( rc, adj );

rc = 1;

adj = " medium hot, sweet ";

Pat At(varName)

the name of a variable to store the result in.

Constructs a pattern that matches the null string and stores the current position in the source string into the specified JSL variable (varName). The assignment is immediate, and the variable can be used with expr() to affect the remainder of the match.

p = ":" + Pat At( listStart ) + Expr(

	If( listStart == 1,

		Pat Immediate( Pat Len( 3 ), early ),

		Pat Immediate( Pat Len( 2 ), late )

);

early = "";

late = "";

Pat Match( ":123456789", p );

Show( early, late );

early = "";

late = "";

Pat Match( "   :123456789", p );

Show( early, late );

First this is produced:

early = "123"

late = ""

and later this:

early = ""

late = "12"

Pat Break("string")

Constructs a pattern that matches zero or more characters that are not in its argument; it stops or breaks on a character in its argument. It fails if a character in its argument is not found (in particular, it fails to match if it finds the end of the source string without finding a break character).

Pat Concat(pattern1, pattern2 <pattern 3, ...>)

Pattern1 + Pattern2 + ...

Constructs a pattern that matches each pattern argument in turn.

A pattern.

Pat Conditional(pattern, varName)

Two or more patterns.

Saves the result of the pattern match, if it succeeds, to a variable named as the second argument (varName) after the match is finished.

the name of a variable to store the result in.

varName

type = "undefined";

rc = Pat Match(

	"green apples",

	Pat Conditional( "red" | "green", type ) + " apples"

);

Show( rc, type );

rc = 1;

type = "green";

Pat Fail()

Constructs a pattern that fails whenever the matcher attempts to move forward through it. The matcher backs up and tries different alternatives. If and when there are no alternatives left, the match fails and Pat Match returns 0.

Constructs a pattern that succeeds and matches the null string when the matcher moves forward through it, but fails when the matcher tries to back up through it. It is a one-way trap door that can be used to optimize some matches.

0 when a match fails.

1 when the match succeeds, 0 otherwise.

Pat Immediate(pattern, varName)

none

Saves the result of the pattern match to a variable named as the second argument (varName) immediately.

the name of a variable to store the result in.

varName

Even though the match failed, the immediate assignment was made.

type = "undefined";

rc = Pat Match(

	"green apples",

	("red" | "green") >> type + " pears"

);

Show( rc, type );

rc = 0

type = "green"

Pat Len(int)

Constructs a pattern that matches n characters.

an integer that specifies the number of characters.

Pat Match(SourceText, Pattern, <ReplacementText>, <NULL>, <ANCHOR>, <MATCHCASE>, <FULLSCAN>)

Pat Match executes the Pattern against the SourceText. The pattern must be constructed first, either inline or by assigning it to a JSL variable elsewhere.

1 if the pattern is found, 0 otherwise.

Arguments

SourceText

A string or string variable that contains the text to be searched.

Pattern

A pattern or pattern variable that contains the text to be searched for.

ReplacementText

Optional string that defines text to replace the pattern in the source text.

NULL

A placeholder for the third argument if ANCHOR, MATCHCASE, or FULLSCAN are necessary and there is no replacement text.

ANCHOR

Optional command to start the pattern match to the beginning of the string. The following match fails because the pattern, “cream”, is not found at the beginning of the string:

Pat Match( "coffee with cream and sugar", "cream", NULL, ANCHOR );

MATCHCASE

Optional command to consider capitalization in the match. By default, Pat Match() is case insensitive.

FULLSCAN

Optional command to force Pat Match to try all alternatives, which uses more memory as the match expands. By default, Pat Match() does not use FULLSCAN, and makes some assumptions that allow the recursion to stop and the match to succeed.

Pat Not Any("string")

Constructs a pattern that matches a single character that is not in the argument.

Constructs patterns that match the null string if the current position is int from the left end of the string, and fail otherwise.

Pat R Pos(int)

Constructs patterns that match the null string if the current position is int from the right end of the string, and fails otherwise.

Pat R Tab(int)

Constructs a pattern that matches up to position n from the end of the string. It can match 0 or more characters. It fails if it would have to move backwards or beyond the end of the string.

Pat Regex(string)

Pat Repeat(pattern, minimum, maximum, GREEDY|RELUCTANT)

Constructs a pattern that matches the regular expression in the quoted string argument.

Constructs a pattern that matches the remainder of the string. It is equivalent to Pat R Tab(0).

Matches pattern between minimum and maximum times.

An integer that must be smaller than maximum.

minimum

maximum

An integer that must be greater than minimum.

GREEDY|RELUCTANT

If GREEDY is specified, it tries the maximum first and works back to the minimum. If RELUCTANT is specified, it tries the minimum first and works up to the maximum.

Notes

Pat Arbno(p) is the same as Pat Repeat(p, 0, infinity, RELUCTANT)

Pat Repeat(p) is the same as Pat Repeat(p, 1, infinity, GREEDY)

Pat Repeat(p, n) is the same as Pat Repeat(p, n, infinity, GREEDY)

Pat Repeat(p, n, m) is the same as Pat Repeat(p, n, m, GREEDY)

Pat Span("string")

Constructs a pattern that matches one or more (not zero) occurrences of characters in its argument. It is greedy; it always matches the longest possible string. It fails rather than matching zero characters.

Constructs a pattern that matches its string argument.

Constructs a pattern that always succeeds, even when the matcher backs into it. It matches the null string.

1 when the match succeeds.

Constructs a pattern that matches forward to position int in the source string. It can match 0 or more characters. It fails if it would have to move backwards or beyond the end of the string.

Pat Test(expr)

Constructs a pattern that succeeds and matches the null string if expr is not zero and fails otherwise.

Usually the argument is wrapped with expr() because the test needs to be made on the current value of variables set by Pat Immediate, Pat Conditional, and Pat At. Without expr, the test is based on values that were known when the pattern was constructed, which means the test always succeeds or always fails at pattern execution time, which is probably not what you want.

Regex Match(source, pattern, <MATCHCASE>)

nCats = 0;

whichCat = 3;

string = "catch a catnapping cat in a catsup factory";

rc = Pat Match(

	string,

	"cat" + Pat Test(

		Expr(

			nCats = nCats + 1;

			nCats == whichCat;

),

	"dog"

);

Show( rc, string, nCats );

rc = 1

string = "catch a catnapping dog in a catsup factory"

nCats = 3