syntax

问题 I would like to parse sentences in propositional logic using BNFC. I wrote the following BNF grammar to facilitate this: Negation. N ::= "(" "-" L")"; Conjuction. C ::= "(" L "&" L ")"; Disjuction. D ::= "(" L "|" L ")"; Implication. I ::= "(" L "=>" L ")"; Equivalence. E ::= "(" L "<=>" L ")"; Atom. L ::= Ident | N | C | D | I | E ; However, with this construction I get the following error: syntax error at line 6, column 27 before `|' What is syntactically incorrect about the specification I

问题 In this answer the OP used: static int const var = 5; in the context of a Conditional Compilation Control. Is there a difference between using static const int and static int const ? Like for example: static const int var; vs. static int const var; I don´t know the technique to imply the type in the middle between static and const . Is there a difference? 回答1: The grammar for declaration specifiers is given in C 2018 6.7 1, and it shows that specifiers for storage class (such as static ),

问题 With Python 3.8 Assignment Expressions have been introduced, allowing to assign values in conditionals and lambdas as such: if x := True: print(x) However it appears this does not extends to attribute assignment, as trying to do something like this from typing import NamedTuple class Test(NamedTuple): field : bool test = Test(field=False) if test.field := True: print(test.field) Will result in the following error: SyntaxError: cannot use named assignment with attribute Is it really only

问题 With Python 3.8 Assignment Expressions have been introduced, allowing to assign values in conditionals and lambdas as such: if x := True: print(x) However it appears this does not extends to attribute assignment, as trying to do something like this from typing import NamedTuple class Test(NamedTuple): field : bool test = Test(field=False) if test.field := True: print(test.field) Will result in the following error: SyntaxError: cannot use named assignment with attribute Is it really only

问题 I was reading about list monads and encountered: [1,2] >>= \n -> ['a','b'] >>= \ch -> return (n,ch) it produces [(1,'a'),(1,'b'),(2,'a'),(2,'b')] Here's how I understand it: Implicit parentheses are: ([1,2] >>= \n -> ['a','b']) >>= (\ch -> return (n,ch)) ([1,2] >>= \n -> ['a','b']) should give [('a',1),('b',1),('a',2),('b',2)] because instance Monad [] where return x = [x] xs >>= f = concat (map f xs) -- this line fail _ = [] so concat (map f xs) is concat (map (\n -> ['a','b']) [1,2]) which

问题 I was reading about list monads and encountered: [1,2] >>= \n -> ['a','b'] >>= \ch -> return (n,ch) it produces [(1,'a'),(1,'b'),(2,'a'),(2,'b')] Here's how I understand it: Implicit parentheses are: ([1,2] >>= \n -> ['a','b']) >>= (\ch -> return (n,ch)) ([1,2] >>= \n -> ['a','b']) should give [('a',1),('b',1),('a',2),('b',2)] because instance Monad [] where return x = [x] xs >>= f = concat (map f xs) -- this line fail _ = [] so concat (map f xs) is concat (map (\n -> ['a','b']) [1,2]) which

问题 I have the following in .bat that is (this works): "%winscp%" /ini=nul ^ /log=C:\TEMP\winscplog.txt ^ /command "open scp://goofy:changeme@10.61.10.225/ -hostkey=""ssh-rsa 2048 d4:1c:1a:4c:c3:60:d5:05:12:02:d2:d8:d6:ae:6c:5d""" ^ "put ""%outfile%"" /home/public/somedir/somesubdir/%basename%" ^ "exit" I have tried to duplicate that into a powershell script like this: & $winscp "/ini=nul" ` "/log=C:\TEMP\winscplog.txt" ` "/command" 'open sftp://goofy:changeme@10.61.10.225/ -hostkey="ssh-rsa 2048

问题 I have the following in .bat that is (this works): "%winscp%" /ini=nul ^ /log=C:\TEMP\winscplog.txt ^ /command "open scp://goofy:changeme@10.61.10.225/ -hostkey=""ssh-rsa 2048 d4:1c:1a:4c:c3:60:d5:05:12:02:d2:d8:d6:ae:6c:5d""" ^ "put ""%outfile%"" /home/public/somedir/somesubdir/%basename%" ^ "exit" I have tried to duplicate that into a powershell script like this: & $winscp "/ini=nul" ` "/log=C:\TEMP\winscplog.txt" ` "/command" 'open sftp://goofy:changeme@10.61.10.225/ -hostkey="ssh-rsa 2048

问题 Maybe a facepalm for you guys, but as a SQL query newbie, I'm having a syntax issue. Anyone know what's wrong? SELECT * FROM company C OUTER JOIN company_address A ON C.company_id = A.company_id WHERE A.company_id IS NULL Giving the error: #1064 - You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'OUTER JOIN company_address A ON C.company_id = A.company_id WHERE A.address_id ' at line 2 回答1: In MySQL you

问题 Maybe a facepalm for you guys, but as a SQL query newbie, I'm having a syntax issue. Anyone know what's wrong? SELECT * FROM company C OUTER JOIN company_address A ON C.company_id = A.company_id WHERE A.company_id IS NULL Giving the error: #1064 - You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'OUTER JOIN company_address A ON C.company_id = A.company_id WHERE A.address_id ' at line 2 回答1: In MySQL you