☜	$PIECE 1984 Version of ANSI Standard					☞

3.2.8 Functions function

$P[IECE] ( expr₁ , expr₂ )

is defined here with the aid of a function, NF, which is used for definitional purposes only, called "find the position number following the mth occurrence".

NF(s,d,m) is defined, for strings s, d, and integer in, as follows:

• When d is the empty string, the result is zero.
• When m ≤ 0, the result is zero.
• When d is not a substring of s, i.e., when $F(s,d) = 0, then the result is $L(s) + $L(d) + 1.
• Otherwise, NF(s,d,1) $F(s,d).
• For m > 1, NF(s,d,m) = NF($E(s,$F(s,d),$L(s)),d,m–1) + $F(s,d) - 1.
• That is, NF generalizes $F to give the position number of the character to the right of the mth occurrence of the string d in s.

Let s be the value of expr₁, and let d be the value of expr₂. $P(s,d) returns the substring of s bounded on the right but not including the first (leftmost) occurrence of d.

$P(s,d) = $E(s,O,NF(s,d,1) - $L(d) - 1).

$P[IECE]( expr₁ , expr₂ , intexpr₃ )

Let m be the integer value of intexpr₃. $P(s,d,m) returns the substring of s bounded by but not including the m-lth and the mth occurrence of d.

$P(s,d,m) _ $E(s,NF(s,d,m–1),NF(s,d,m) - $L(d) - 1).

$P[IECE]( expr₁ , expr₂ , intexpr₃ , intexpr₄ )

Let n be the integer value of intexpr₄. $P(s,d,m,n) returns the substring of s bounded on the left but not including the m–1th occurrence of d in s, and bounded on the right but not including the nth occurrence of d in s.

$P(s,d,m,n) _ $E(s,NF(s,d,m–1),NF(s,d,n) - $L(d) - 1).

Note that $P(s,d,m,m) - $P(s,d,m), and that $P(s,d,1) - $P(s,d).

See also the transition diagram for $Piece.

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Copyright © Annotations: 2003-2008 Jacquard Systems Research
Copyright © Annotations: 2008-2024 Ed de Moel.

This page most recently updated on 15-Nov-2023, 13:11:13.

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