ToC DocOverview CGDoc RelNotes Index PermutedIndex
Allegro CL
Home Previous Up Next Table of Contents Index
  ANSI Common Lisp   23 Reader   23.1 Reader Concepts   23.1.3 Argument Conventions of Some Reader Functions The EOF-ERROR-P argument

Eof-error-p in input function calls controls what happens if input is from a file (or any other input source that has a definite end) and the end of the file is reached. If eof-error-p is true (the default), an error of type end-of-file is signaled at end of file. If it is false, then no error is signaled, and instead the function returns eof-value.

Functions such as read that read the representation of an object rather than a single character always signals an error, regardless of eof-error-p, if the file ends in the middle of an object representation. For example, if a file does not contain enough right parentheses to balance the left parentheses in it, read signals an error. If a file ends in a symbol or a number immediately followed by end-of-file, read reads the symbol or number successfully and when called again will act according to eof-error-p. Similarly, the function read-line successfully reads the last line of a file even if that line is terminated by end-of-file rather than the newline character. Ignorable text, such as lines containing only whitespace2 or comments, are not considered to begin an object; if read begins to read an expression but sees only such ignorable text, it does not consider the file to end in the middle of an object. Thus an eof-error-p argument controls what happens when the file ends between objects.

Home Previous Up Next Table of Contents Index
© Franz Inc. All Rights Reserved - File last updated 2022-07-25