String¶

Status: Stable

documented, exercised by the test suite and/or worked examples, with no known limitations recorded.

Description¶

String

is the head of string objects. As a type specification in Read and ReadList it reads a line, up to a newline.

Examples (3)¶

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

Applications (3)¶

String is the head of string objects

In[1]:= Head["abc"]
Out[1]= String

So _String matches any string

In[2]:= MatchQ["abc", _String]
Out[2]= True

The bare symbol String is itself a Symbol

In[3]:= Head[String]
Out[3]= Symbol

Performance¶

Against other systems, from the benchmark suite (same input, results cross-checked for agreement):

case	Mathilda	Wolfram	Python
Characters of 200k chars	4.38 s	2.54 s	0.419 s
StringSplit on space, 200k chars	3.12 s	4.13 s	0.723 s
StringCases regex, 200k chars	2.36 s	3.69 s	3.34 s
StringReplace regex, 200k chars	1.97 s	4.74 s	3.35 s
StringReplace literal, 200k chars	0.332 s	1.17 s	0.195 s
StringCount substring, 200k chars	0.224 s	0.364 s	0.102 s

Implementation notes¶

Definition. String has two roles. Primarily it is the head of string objects: a string leaf is an EXPR_STRING, and Head of one returns the symbol String, so _String is the pattern that matches any string. Secondarily it is a type specification in Read and ReadList, where it reads one line (up to a newline). The symbol itself is inert — no builtin, no value; its docstring is in info.c.

Representation. Strings are stored as EXPR_STRING nodes carrying a C string, not as String[...] compounds; String is the head those leaves report, supplied by the Head builtin in src/core.c (the EXPR_STRING case), which is why StringQ/MatchQ[..., _String] work. As a read type, the scanner in src/io/read.c maps n == SYM_String to the RT_STRING read tag, whose reader returns the next line as a string. The bare symbol String is itself an EXPR_SYMBOL, so Head[String] is Symbol.

Usage & limits. The head role is pervasive — any pattern, type test, or Cases/Select over strings leans on it. The read-type role needs a file or open stream, so it cannot be exercised on a bare literal. String performs no computation on its own in either role.

Attributes: none registered.

References¶

Source: src/core.c
Specification index: Mathilda_spec.md

Notes & additional examples¶

Notes¶

String is the head carried by string leaves — Head["text"] is String, which is what makes _String match any string in a pattern, type test, or Cases/Select. Strings are stored as EXPR_STRING nodes, not as String[...] compounds, so String appears as a head but never wraps anything. It is also a Read/ReadList type specification that reads one line (up to a newline); that role needs a file or open stream to exercise. The bare symbol String is an ordinary Symbol.