Basically, using the following code on a file stream, I get the following:
$basis = $2 * 1.0;
$cost = ($basis - 2500.0) ** 1.05;
# The above should ensure that both cost & basis are floats
printf " %f -> %f", $basis, $cost;
if ($basis gt $cost) { # <- *** THIS WAS MY ERROR: gt forces lexical!
$cost = $basis;
printf " -> %f", $cost;
}
Outputs:
10667.000000 -> 12813.438340
30667.000000 -> 47014.045519
26667.000000 -> 40029.842300
66667.000000 -> 111603.373367 -> 66667.000000
8000.000000 -> 8460.203780
10667.000000 -> 12813.438340
73333.000000 -> 123807.632158 -> 73333.000000
6667.000000 -> 6321.420427 -> 6667.000000
80000.000000 -> 136071.379474 -> 80000.000000
As you can see, for most values, the code appears to work fine.
But for some values.... 66667, 80000, and a few others, ActivePerl 5.14 tells me that 66667 > 1111603!!!
Does anyone know anything about this - or have an alternate Perl interpreter I might use (Windows). Because this is ridiculous.
You are using a lexical comparison instead of the numerical one
$cost = ($basis - 2500.0) ** 1.05;
printf " %f -> %f", $basis, $cost;
if ($basis > $cost) {
$cost = $basis;
printf " -> %f", $cost;
}
ps: revised to match the updated question
The first few chapters of Learning Perl will clear this up for you. Scalar values are can be either strings or numbers, or both at the same time. Perl uses the operator to decide how to treat them. If you want to do numeric comparisons, you use the numeric comparison operators. If you want to do string comparisons, you use the string comparison operators.
The scalar values themselves don't have a type, despite other answers and comments using words like "float" and "cast". It's just strings and numbers.
Not sure why you need to compare as lexical, but you can force it using sprintf
$basis_real = sprintf("%015.6f",$basis);
$cost_real = sprintf("%015.6f",$cost);
printf " %s -> %s", $basis_real, $cost_real;
if ($basis_real gt $cost_real) {
$cost = $basis;
printf " -> %015.6f", $cost;
}
Output:
00010667.000000 -> 00012813.438340
00030667.000000 -> 00047014.045519
00026667.000000 -> 00040029.842300
00066667.000000 -> 00111603.373367
00008000.000000 -> 00008460.203780
00010667.000000 -> 00012813.438340
00073333.000000 -> 00123807.632158
00006667.000000 -> 00006321.420427 -> 00006667.000000
00080000.000000 -> 00136071.379474
The reason it was failing as you noted, the lexical compare does character to character compare, so when it hits the decimal point in 6667. it actually is alphabetically before 111603. , so it is greater.
To fix this, you must make all the numbers the same size, especially where the decimal lines up. The %015 is the total size of number, including the period and the decimals.
Related
I need to build a lexical analyzer using Gocc, however no option to ignore case is mentioned in the documentation and I haven't been able to find anything related. Anyone have any idea how it can be done or should I use another tool?
/* Lexical part */
_digit : '0'-'9' ;
int64 : '1'-'9' {_digit} ;
switch: 's''w''i''t''c''h';
while: 'w''h''i''l''e';
!whitespace : ' ' | '\t' | '\n' | '\r' ;
/* Syntax part */
<<
import(
"github.com/goccmack/gocc/example/calc/token"
"github.com/goccmack/gocc/example/calc/util"
)
>>
Calc : Expr;
Expr :
Expr "+" Term << $0.(int64) + $2.(int64), nil >>
| Term
;
Term :
Term "*" Factor << $0.(int64) * $2.(int64), nil >>
| Factor
;
Factor :
"(" Expr ")" << $1, nil >>
| int64 << util.IntValue($0.(*token.Token).Lit) >>
;
For example, for "switch", I want to recognize no matter if it is uppercase or lowercase, but without having to type all the combinations. In Bison there is the option % option caseless, in Gocc is there one?
Looking through the docs for that product, I don't see any option for making character literals case-insensitive, nor do I see any way to write a character class, as in pretty well every regex engine and scanner generator. But nothing other than tedium, readability and style stops you from writing
switch: ('s'|'S')('w'|'W')('i'|'I')('t'|'T')('c'|'C')('h'|'H');
while: ('w'|'W')('h'|'H')('i'|'I')('l'|'L')('e'|'E');
(That's derived from the old way of doing it in lex without case-insensitivity, which uses character classes to make it quite a bit more readable:
[sS][wW][iI][tT][cC][hH] return T_SWITCH;
[wW][hH][iI][lL][eE] return T_WHILE;
You can come closer to the former by defining 26 patterns:
_a: 'a'|'A';
_b: 'b'|'B';
_c: 'c'|'C';
_d: 'd'|'D';
_e: 'e'|'E';
_f: 'f'|'F';
_g: 'g'|'G';
_h: 'h'|'H';
_i: 'i'|'I';
_j: 'j'|'J';
_k: 'k'|'K';
_l: 'l'|'L';
_m: 'm'|'M';
_n: 'n'|'N';
_o: 'o'|'O';
_p: 'p'|'P';
_q: 'q'|'Q';
_r: 'r'|'R';
_s: 's'|'S';
_t: 't'|'T';
_u: 'u'|'U';
_v: 'v'|'V';
_w: 'w'|'W';
_x: 'x'|'X';
_y: 'y'|'Y';
_z: 'z'|'Z';
and then explode the string literals:
switch: _s _w _i _t _c _h;
while: _w _h _i _l _e;
Do you gain any performance, even if it's minor, by chaining function calls as shown below or is it just coding style preference?
execute() ->
step4(step3(step2(step1())).
Instead of
execute() ->
S1 = step1(),
S2 = step2(S1),
S3 = step3(S2),
step4(S3).
I was thinking whether in the 2nd version the garbage collector has some work to do for S1, S2, S3. Should that apply for the 1st version as well?
They are identical after compilation. You can confirm this by running the erl file through erlc -S and reading the generated .S file:
$ cat a.erl
-module(a).
-compile(export_all).
step1() -> ok.
step2(_) -> ok.
step3(_) -> ok.
step4(_) -> ok.
execute1() ->
step4(step3(step2(step1()))).
execute2() ->
S1 = step1(),
S2 = step2(S1),
S3 = step3(S2),
step4(S3).
$ erlc -S a.erl
$ cat a.S
{module, a}. %% version = 0
...
{function, execute1, 0, 10}.
{label,9}.
{line,[{location,"a.erl",9}]}.
{func_info,{atom,a},{atom,execute1},0}.
{label,10}.
{allocate,0,0}.
{line,[{location,"a.erl",10}]}.
{call,0,{f,2}}.
{line,[{location,"a.erl",10}]}.
{call,1,{f,4}}.
{line,[{location,"a.erl",10}]}.
{call,1,{f,6}}.
{call_last,1,{f,8},0}.
{function, execute2, 0, 12}.
{label,11}.
{line,[{location,"a.erl",12}]}.
{func_info,{atom,a},{atom,execute2},0}.
{label,12}.
{allocate,0,0}.
{line,[{location,"a.erl",13}]}.
{call,0,{f,2}}.
{line,[{location,"a.erl",14}]}.
{call,1,{f,4}}.
{line,[{location,"a.erl",15}]}.
{call,1,{f,6}}.
{call_last,1,{f,8},0}.
...
As you can see, both execute1 and execute2 result in identical code (the only thing different are line numbers and label numbers.
I have a variable of type float. Xcode displays it using scientific notation (i.e. 3.37626e+07). I'm trying to get it to display using dot notation (i.e. 33762616.00).
I've tried every format provided by lldb, but none displays the float using decimals. I read other posts and watched the WWDC2012 session 415 (as suggested here), but I must be too close the forest to see the trees. Any help would be greatly appreciated!
Try adding a custom data formatter in your ~/.lldbinit file for type float. e.g.
Process 13204 stopped
* thread #1: tid = 0xb6f8d, 0x0000000100000f33 a.out`main + 35 at a.c:5, stop reason = step over
#0: 0x0000000100000f33 a.out`main + 35 at a.c:5
2 int main ()
3 {
4 float f = 33762616.0;
-> 5 printf ("%f\n", f);
6 }
(lldb) p f
(float) $0 = 3.37626e+07
(lldb) type summ add -v -o "return '%f' % valobj.GetData().GetFloat(lldb.SBError(), 0)" float
(lldb) p f
(float) $1 = 33762616.000000
(lldb)
The default set of formatters provided by lldb can't do this, but dropping into Python allows you a lot of flexibility.
I am new to Haskell. Previously I have programmed in Python and Java. When I am debugging some code I have a habit of littering it with print statements in the middle of code. However doing so in Haskell will change semantics, and I will have to change my function signatures to those with IO stuff. How do Haskellers deal with this? I might be missing something obvious. Please enlighten.
Other answers link the official doco and the Haskell wiki but if you've made it to this answer let's assume you bounced off those for whatever reason. The wikibook also has an example using Fibonacci which I found more accessible. This is a deliberately basic example which might hopefully help.
Let's say we start with this very simple function, which for important business reasons, adds "bob" to a string, then reverses it.
bobreverse x = reverse ("bob" ++ x)
Output in GHCI:
> bobreverse "jill"
"llijbob"
We don't see how this could possibly be going wrong, but something near it is, so we add debug.
import Debug.Trace
bobreverse x = trace ("DEBUG: bobreverse" ++ show x) (reverse ("bob" ++ x))
Output:
> bobreverse "jill"
"DEBUG: bobreverse "jill"
llijbob"
We are using show just to ensure x is converted to a string correctly before output. We also added some parenthesis to make sure the arguments were grouped correctly.
In summary, the trace function is a decorator which prints the first argument and returns the second. It looks like a pure function, so you don't need to bring IO or other signatures into the functions to use it. It does this by cheating, which is explained further in the linked documentation above, if you are curious.
Read this. You can use Debug.Trace.trace in place of print statements.
I was able to create a dual personality IO / ST monad typeclass, which will print debug statements when a monadic computation is typed as IO, them when it's typed as ST. Demonstration and code here: Haskell -- dual personality IO / ST monad? .
Of course Debug.Trace is more of a swiss army knife, especially when wrapped with a useful special case,
trace2 :: Show a => [Char] -> a -> a
trace2 name x = trace (name ++ ": " ++ show x) x
which can be used like (trace2 "first arg" 3) + 4
edit
You can make this even fancier if you want source locations
{-# LANGUAGE TemplateHaskell #-}
import Language.Haskell.TH
import Language.Haskell.TH.Syntax as TH
import Debug.Trace
withLocation :: Q Exp -> Q Exp
withLocation f = do
let error = locationString =<< location
appE f error
where
locationString :: Loc -> Q Exp
locationString loc = do
litE $ stringL $ formatLoc loc
formatLoc :: Loc -> String
formatLoc loc = let file = loc_filename loc
(line, col) = loc_start loc
in concat [file, ":", show line, ":", show col]
trace3' (loc :: String) msg x =
trace2 ('[' : loc ++ "] " ++ msg) x
trace3 = withLocation [| trace3' |]
then, in a separate file [from the definition above], you can write
{-# LANGUAGE TemplateHaskell #-}
tr3 x = $trace3 "hello" x
and test it out
> tr3 4
[MyFile.hs:2:9] hello: 4
You can use Debug.Trace for that.
I really liked Dons short blog about it:
https://donsbot.wordpress.com/2007/11/14/no-more-exceptions-debugging-haskell-code-with-ghci/
In short: use ghci, example with a program with code called HsColour.hs
$ ghci HsColour.hs
*Main> :set -fbreak-on-exception
*Main> :set args "source.hs"
Now run your program with tracing on, and GHCi will stop your program at the call to error:
*Main> :trace main
Stopped at (exception thrown)
Ok, good. We had an exception… Let’s just back up a bit and see where we are. Watch now as we travel backwards in time through our program, using the (bizarre, I know) “:back” command:
[(exception thrown)] *Main> :back
Logged breakpoint at Language/Haskell/HsColour/Classify.hs:(19,0)-(31,46)
_result :: [String]
This tells us that immediately before hitting error, we were in the file Language/Haskell/HsColour/Classify.hs, at line 19. We’re in pretty good shape now. Let’s see where exactly:
[-1: Language/Haskell/HsColour/Classify.hs:(19,0)-(31,46)] *Main> :list
18 chunk :: String -> [String]
vv
19 chunk [] = head []
20 chunk ('\r':s) = chunk s -- get rid of DOS newline stuff
21 chunk ('\n':s) = "\n": chunk s
^^
When printing string with StyleBox by default we get nicely formatted numbers inside string:
StyleBox["some text 1000000"] // DisplayForm
I mean that the numbers look as if would have additional little spaces: "1 000 000".
But in Messages all numbers are displayed without formatting:
f::NoMoreMemory =
"There are less than `1` bytes of free physical memory (`2` bytes \
is free). $Failed is returned.";
Message[f::NoMoreMemory, 1000000, 98000000]
Is there a way to get numbers inside Messages to be formatted?
I'd use Style to apply the AutoNumberFormatting option:
You can use it to target specific messages:
f::NoMoreMemory =
"There are less than `1` bytes of free physical memory (`2` bytes is free). $Failed is returned.";
Message[f::NoMoreMemory,
Style[1000000, AutoNumberFormatting -> True],
Style[98000000, AutoNumberFormatting -> True]]
or you can use it with $MessagePrePrint to apply it to all the messages:
$MessagePrePrint = Style[#, AutoNumberFormatting -> True] &;
Message[f::NoMoreMemory, 1000000, 98000000]
I think you want $MessagePrePrint
$MessagePrePrint =
NumberForm[#, DigitBlock -> 3, NumberSeparator -> " "] &;
Or, incorporating Sjoerd's suggestion:
With[
{opts =
AbsoluteOptions[EvaluationNotebook[],
{DigitBlock, NumberSeparator}]},
$MessagePrePrint = NumberForm[#, Sequence ## opts] &];
Adapting Brett Champion's method, I believe this allows for copy & paste as you requested:
$MessagePrePrint = StyleForm[#, AutoNumberFormatting -> True] &;