EmptyLine: Recognize empty lines

In parcr: Construct Parsers for Structured Text Files

Recognize empty lines

Description

An empty line is a line that consists entirely of space-like characters. EmptyLine is a parser that recognizes one empty line, Spacer recognizes one or more empty lines and MaybeEmpty recognizes zero or more empty lines. EmptyLine returns the empty line but Spacer and MaybeEmpty discard these.

Usage

EmptyLine()

Spacer()

MaybeEmpty()

Value

A parser.

Pseudocode

space_like_eraser(x):
    d = x in which all "\\s+" are replaced by ""
    if d=="" TRUE else FALSE

Emptyline: satisfy(space_like_eraser)

Spacer: one_or_more(EmptyLine()) %ret% null

MaybeEmpty: zero_or_more(EmptyLine()) %ret% null

where null is the empty vector.

Examples

EmptyLine() (" \t  ") # success
EmptyLine() ("    .") # failure
EmptyLine() ("") # success
Spacer() (c("   \t  ", "    ", "abc"))
Spacer() (c("            ", "    ", "Important text"))
Spacer() (c("Important text")) # failure, missing empty line
MaybeEmpty() (c("            ", "    ", "Important text")) # success, just as Spacer()
MaybeEmpty() (c("Important text")) # success, in contrast to Spacer()

parcr documentation built on Aug. 8, 2025, 6:20 p.m.