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NullWords

Status: Experimental

present and registered, but lightly documented and not yet covered by dedicated tests.

Description

NullWords

is an option for Read and ReadList specifying whether a null word is assumed between two adjacent word separators. The default is False.

Examples (5)

Every input below was run against the current Mathilda build and its output recorded.

Applications (5)

A bare Read/ReadList option symbol

In[1]:= Head[NullWords]
Out[1]= Symbol

The default is False

In[2]:= Options[ReadList, NullWords]
Out[2]= {NullWords -> False}

In[3]:= str = OpenWrite["/tmp/mathilda_nw.txt"]; WriteString[str, "a  b\n"]; Close[str];

Default: the empty field is skipped

In[4]:= ReadList["/tmp/mathilda_nw.txt", Word]
Out[4]= {"a", "b"}

Now kept as ""

In[5]:= ReadList["/tmp/mathilda_nw.txt", Word, NullWords -> True]
Out[5]= {"a", "", "b"}

Implementation notes

Definition. NullWords is an option name for Read and ReadList specifying whether a null (empty) word is assumed between two adjacent word separators. It is a bare option symbol, not a function — no builtin, no DownValues, not even the Protected attribute — carrying only the docstring in info_init (src/info.c). The reader src/io/read.c reads it out of the option list (its default NullWords -> False is part of Options[Read] / Options[ReadList]).

Representation. NullWords stays an inert EXPR_SYMBOL, appearing only on the left of a rule; FullForm[NullWords -> True] is Rule[NullWords, True]. The value is a boolean; the default is False.

Usage & limits. With NullWords -> False (the default) the word reader skips an empty field between adjacent separators — two spaces read as one gap. With NullWords -> True it emits an empty string "" for that field, so "a b" reads as {"a", "", "b"}. It is one of the tokenisation options alongside WordSeparators, TokenWords, RecordSeparators and NullRecords, all defaulting from Options[Read] so SetOptions[Read, ...] adjusts them globally.

Attributes: none registered.

References

Notes & additional examples

Notes

NullWords is an option for Read and ReadList deciding whether an empty word is assumed between two adjacent word separators. It is an inert option-name symbol — no builtin, no DownValues — read out of a call's option list by the reader.

The default False makes the word reader skip the empty field, so the double space above reads as {"a", "b"}; NullWords -> True keeps it, giving {"a", "", "b"}. It is one of the tokenisation options (with WordSeparators, TokenWords, RecordSeparators, NullRecords), all defaulting from Options[Read], so SetOptions[Read, NullWords -> True] would change the global default.