3 ms·

The style reminds me of some J implementations! #define DO(n,x) {I i=0,_n=(n);for(;i<_n;++i){x;}} http://code.jsoftware.com/wiki/Essays/Incunabulum http://

• jnordwick 10y ago
  I think Arthur Whitney's (in)famous code makes its way to HN about once a year.
  • agumonkey 10y ago
    #A=As #I=it #S=sh #o=o #u=uld A I Sou
• dangerbird2 10y ago
  The worst part of that macro is that it is inherently unhygienic: it leaks the variable name 'i' up the scope
  • jacquesm 10y ago
    Presumably there is a #define I int floating around somewhere so that need not be the case (note the capital I inside the curly brace).
    • dangerbird2 10y ago
      the Big "I" is the type, which is a macro parameter. The variable name "i" is not a parameter. If There is another variable "i" in the scope, the loop variable will shadow it in the DO statement. Something like this float i = 10; DO({i+= 10;} 20); will evaluate to this, modifying the "i" declared inside the macro float i_1 = 10; {I i_2=0,_n=(n);for(;i_2<_n;++i_2){i_2 += 10;}}
      • jacquesm 10y ago
        Hm, in the linked page there is a typedef long for I. typedef long I; #define DO(n,x) {I i=0,_n=(n);for(;i<_n;++i){x;}} (I added a comma here after the }, 20 is the x parameters) DO({i+= 10;}, 20); expands to: typedef long I; {I i=0,_n=({i+= 10;});for(;i<_n;++i){20;}}; The '20' presumably should have been some kind of function call or action to repeat and the 'n' should have been the count (the reverse from your example). So that would make this: typedef long I; {I i=0,_n=(20);for(;i<_n;++i){ i+= 10; }}; You're still right that it will shadow any 'i' declared outside and so it won't work but it will not overwrite it as far as I can see. You'll just end up right where you started. What I really don't get is if they're going to use _n for the count anyway why not count it down to 0, that way the whole 'i' could be avoided. (you'd still have a problem with _n but that could be overcome with a convention, which of course someone will forget with some nasty bug as a result)
• dangerbird2 10y ago
  The worst part of that macro is that it is inherently unhygienic: it leaks the variable name 'i' up the scope