Elisp function to replace underscores for white spaces in the current line - elisp

Question

I'm trying to write a very simple function to replace all the underscores in the current line for whites paces.
This is what I have so far
(select-current-line)
(exit-minibuffer)
(query-replace "_" " " nil (if (and transient-mark-mode mark-active) (region-beginning)) (if (and transient-mark-mode mark-active) (region-end)))
But I get the following message:
No catch for tag: exit, nil
I'm not very convinced that using query-replace in an active selection is the best way, but I am not a elisp programmer at all.
Any ideas?
Thanks
UPDATE:
Based in the answers below, this is the piece code that I ended using:
(let ((end (copy-marker (line-end-position))))
(while (re-search-forward "_" end t)
(replace-match " " nil nil)))

Answer 1

C-h f query-replace RET doesn't say what I wanted to quote, but C-h f perform-replace RET does:
Don't use this in your own program unless you want to query and set the mark
just as `query-replace' does. Instead, write a simple loop like this:
(while (re-search-forward \"foo[ \\t]+bar\" nil t)
(replace-match \"foobar\" nil nil))
As for limiting it to the current line, the best way to do it is to use the second arg of re-search-forward:
(let ((end (copy-marker (line-end-position))))
(while (re-search-forward \"foo[ \\t]+bar\" end t)
(replace-match \"foobar\" nil nil)))
Notice the use of copy-marker because the position of the end-of-line will keep changing as you modify the line, so you don't want to keep the position as a plain integer but as a marker (which is tied to a place in the text).
A common alternative is to go backwards (since insertion/deletions only affect positions after the change):
(end-of-line)
(let ((beg (line-beginning-position)))
(while (re-search-backward \"foo[ \\t]+bar\" beg t)
(replace-match \"foobar\" nil nil)))