从GNU Prolog的文件中读取一行 [英] Reading a line from a file in GNU Prolog
问题描述
如何做一个文件读取一行在GNU Prolog的线? (所以不能访问SWI所具有的方便的功能。)我认为它与get_char / 1和peek_char / 1(检查终止的换行符)有关,但是我尝试实现一个可行的解决方案迄今为止失败了。 / p>
这里是我得到的:
readl_as_list ID,X): -
current_input(ID),
readl_as_list(X)。
readl_as_list([X]): -
(peek_char(NextChar),==(NextChar,'\\\
');
get_code(Char1),
append([X],[Char1],X),
readl_as_list(X))。
printl_list([]): -
!,nl。
printl_list([H | X]): -
put_code(H),printl_list(X)。
将这个加载到解释器中,我得到了(空行为了便于阅读):
|打开('word_list.txt',阅读,ID)。
ID ='$ stream'(2)
是
| - readl_as_list(ID,X)。
ID ='$ stream'(0)
X = [_]?
%(口译员暂停,直到我按回车)
是
| ? - printl_list(X)。
X = []
是
这些行不一定非得以字符列表的形式阅读,但是因为我的目标是搜索匹配某些条件(例如不重复的字母)的单词列表,所以这似乎是最明智的做法。
我写了一个实用程序,获取一行代码。返回end_of_file结束...
read_line_codes(S,SoFar,L): -
get_code(S,C ),
(C == -1
- >(SoFar == []
- > L = end_of_file
; reverse(SoFar,L)
)
;(C == 0'\ $
→> reverse(SoFar,L)
; read_line_codes(S,[C | SoFar],L)
)
)。
测试:
< ('data_grid.pl',read,S),repeat,read_line_codes(S,[],L),format('〜s',[L])。
/ *文件:data_grid.pl
S =< stream>(0x335c9e0),
L = [47,42,32,32,70,105,108,101,58 | ...];
作者:Carlo ,,,
S =< stream>(0x335c9e0),
L = [32,32,32,32,65,117,116,104,111 | ..];
创建时间:2011年10月20日
S =(0x335c9e0),
L = [32,32, 。];
...
I feel like I'm bashing my head against a wall with something that I assume should be easy. Perhaps my approach is incorrect. I definitely don't feel like I understand the concept behind I/O in Prolog. (Such as: what is the difference between a stream alias and the variable bound by open/3?) But I digress:
How do a read a file line-by-line in GNU Prolog? (So without access to the handy functions that SWI has.) I assume it has something to do with get_char/1 and peek_char/1 (to check for a terminating newline) but my attempts to implement a workable solution have failed so far.
Here is as far as I've gotten:
readl_as_list(ID, X):-
current_input(ID),
readl_as_list(X).
readl_as_list([X]):-
(peek_char(NextChar), ==(NextChar, '\n');
get_code(Char1),
append([X], [Char1], X),
readl_as_list(X)).
printl_list([]):-
!, nl.
printl_list([H|X]):-
put_code(H), printl_list(X).
Loading this into the interpreter, I get (empty lines removed for readability):
| ?- open('word_list.txt', read, ID).
ID = '$stream'(2)
yes
| ?- readl_as_list(ID, X).
ID = '$stream'(0)
X = [_] ?
% (interpreter pauses until I press return)
yes
| ?- printl_list(X).
X = []
yes
The lines don't necessarily have to be read in as character lists, but since my goal is to search through a list of words for ones that match certain conditions (no repeat letters, for example), that seemed the most sensible way to do it.
I wrote an utility, that fetch a line of codes. Returns end_of_file at end...
read_line_codes(S, SoFar, L) :-
get_code(S, C),
( C == -1
-> ( SoFar == []
-> L = end_of_file
; reverse(SoFar, L)
)
; ( C == 0'\n
-> reverse(SoFar, L)
; read_line_codes(S, [C|SoFar], L)
)
).
test:
?- open('data_grid.pl',read,S),repeat,read_line_codes(S,[],L),format('~s',[L]).
/* File: data_grid.pl
S = <stream>(0x335c9e0),
L = [47, 42, 32, 32, 70, 105, 108, 101, 58|...] ;
Author: Carlo,,,
S = <stream>(0x335c9e0),
L = [32, 32, 32, 32, 65, 117, 116, 104, 111|...] ;
Created: Oct 20 2011
S = <stream>(0x335c9e0),
L = [32, 32, 32, 32, 67, 114, 101, 97, 116|...] ;
...
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