CODEWITHSUNDEEP
lispcommon-lisp
Srv19
Srv19

Reputation: 3618

How to handle end-of-file error when using read-from-string?

I am trying to make use of function read-from-string, however i cannot make heads from tails with it.

If i understand documentation correctly, if second parameter is not true, then unbalanced expression in supplied string should not cause an error. However, if in try it out, i get:

> (read-from-string "(1 2" t 'EOF)

Condition of type: END-OF-FILE Unexpected end of file on #<string-input stream from "(1 2">.

Available restarts:

  1. (RESTART-TOPLEVEL) Go back to Top-Level REPL.

Broken at SI:BYTECODES. [Evaluation of: (READ-FROM-STRING "(1 2" ...)] In: #<process TOP-LEVEL>.

>> 1

1

>> (read-from-string "(1 2" nil 'EOF)

Debugger received error of type: END-OF-FILE Unexpected end of file on #<string-input stream from "(1 2">. Error flushed.

No matter shat i send, i always get an error.

I am using ECL 15.3.7

Upvotes: 0

Views: 884

Answers (1)

user5920214
user5920214

Reputation:

The eof-error-p and eof-value optional arguments control the result if you hit the end of the string before finding anything at all. So:

> (read-from-string "")

Error: ...

while

> (read-from-string "" nil 'foo)
foo
0

If the end of the string occurs part-way through an incomplete object an error is always signaled. The spec is clear on this although it's fairly far down the entry:

If the end of the supplied substring occurs before an object can be read, an error is signaled if eof-error-p is true. An error is signaled if the end of the substring occurs in the middle of an incomplete object.

Upvotes: 3

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