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characterswhile

Characterswhile is a conceptual term used in computer science to describe an operation that consumes characters from a string or stream while a given predicate holds for each character. It is not an official keyword in mainstream programming languages, but it is used informally to discuss a common pattern in lexical analysis and text processing.

Formal definition and behavior

Given a string s and a predicate P(character) that returns true or false, characterswhile(s, P) returns the

Algorithmic outline

- Initialize a position index at the start of the string.

- While the current character satisfies P, advance the index.

- Return the substring from the start up to (but not including) the first non-satisfying character.

Applications and variants

Characterswhile is commonly used in tokenization, parsing, and validation tasks to extract runs of characters that

See also

- while loop

- tokenization

- lexical analysis

- prefix extraction

- string processing

longest
prefix
of
s
consisting
of
characters
for
which
P
holds.
In
practice,
it
scans
characters
from
the
start
of
s
until
it
encounters
a
character
for
which
P
is
false,
and
then
returns
the
collected
prefix.
For
example,
characterswhile("abc123",
isLetter)
yields
"abc",
because
the
letters
stop
at
the
first
non-letter.
match
a
rule
(e.g.,
letters,
digits,
whitespace).
Variants
may
apply
the
predicate
to
the
next
character,
a
stream
of
input,
or
to
a
character
class.
It
is
closely
related
to
the
concept
of
scanning
in
regular
expressions
and
lexical
analysis.