EndOfFile¶

Status: Experimental

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

Description¶

EndOfFile

is the symbol returned by Read at the end of a file. ReadList uses it to fill the unread slots of a type sequence truncated by end of file.

Examples (4)¶

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

Applications (4)¶

A bare sentinel symbol, not a function

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

In[2]:= str = OpenWrite["/tmp/mathilda_eof.txt"]; WriteString[str, "only\n"]; Close[str];

In[3]:= ins = OpenRead["/tmp/mathilda_eof.txt"]; Read[ins, Word]; eof = Read[ins, Word]; Close[ins]; eof
Out[3]= EndOfFile

A plain marker value, compared by identity

In[4]:= EndOfFile === EndOfFile
Out[4]= True

Implementation notes¶

Definition. EndOfFile is the sentinel symbol that Read returns when a stream has no more to read. It is a bare symbol, not a function — no builtin, no DownValues, not even the Protected attribute — carrying only the docstring set in info_init (src/info.c). It is produced, not consumed, by the reader src/io/read.c.

Representation. EndOfFile stays an inert EXPR_SYMBOL; evaluated on its own it is just EndOfFile, and Head[EndOfFile] is Symbol. The reader constructs it with expr_new_symbol(SYM_EndOfFile) at the two points where a read runs out of input (the scalar case, and the fallthrough that ends a ReadList loop).

Usage & limits. When Read[stream, type] is called at or past end of file it returns EndOfFile; ReadList uses the same sentinel to fill the unread trailing slots of a type sequence that end-of-file truncated, and stops its loop when it is produced. Code reading a stream incrementally tests for it to know when to stop — While[(x = Read[s, Word]) =!= EndOfFile, ...]. It is a plain marker value with no numeric or structural meaning of its own.

Attributes: none registered.

References¶

Source: src/io/read.c
Specification index: Mathilda_spec.md

Notes & additional examples¶

Notes¶

EndOfFile is the sentinel symbol Read returns at the end of a stream. It is an inert marker — no builtin, no DownValues — produced by the reader (src/io/read.c), not consumed: the second Read[ins, Word] above has already consumed the only word, so it hands back EndOfFile.

ReadList uses the same sentinel to pad the trailing slots of a type sequence that end-of-file truncated, and stops its loop when it appears. Incremental readers test for it by identity, as in While[(x = Read[s, Word]) =!= EndOfFile, ...]. It carries no numeric or structural meaning of its own.