[Coco] The Coco's first webserver, written in Basic09

[Wayne Campbell]

I was beginning with simply parsing an expression. I felt that if I could 
accomplish this, the rest would be easier to figure out. The problem with 
RUN is that it specifically launches a subroutine module (Basic09 I-Code or 
6809 object code), passing to it whatever parameters are required. This 
means that the eval() function , in the statement RUN eval(<string>), is a 
subroutine that does whatever parsing is necessary to evaluate the 
"expression". The parameter, in this case, would be the string to parse.

Wayne


----- Original Message ----- 
From: "Christian Lesage" <hyperfrog at gmail.com>
To: "CoCoList for Color Computer Enthusiasts" <coco at maltedmedia.com>
Sent: Wednesday, December 30, 2009 5:17 PM
Subject: Re: [Coco] The Coco's first webserver, written in Basic09



>I don't understand where you are heading to with this. You would need more 

>than an expression evaluator in order to program a server that can generate 

>dynamic content. In JavaScript, for instance, the eval() function parses 

>the string it is given as a parameter, looking for JavaScript code. If it 

>finds any JavaScript code, it will be executed. If you want to simulate the 

>same behaviour in BASIC09, you will end up writing a complete BASIC09 

>interpreter on top of the underlying one, unless you find a way to inject 

>an arbitrary string in the latter.

>

> Hint: Use RUN.

>

>

>

> Wayne Campbell wrote:

>> OK. I did a little. I really don't know what I'm doing here, but this is 

>> what I got for a start. There are many problems. First, Basic09's 

>> precedence ordering acts on the expression as follows:

>>

>> 2*3+5/2

>>

>> is evaluated as

>>

>> 2*3/2+5, yielding a result of 8

>>

>> To get the result of 5 (what we're looking for), it would have to be 

>> written as

>>

>> (2*3+5)/2 (the remainder of 1 is dropped)

>>

>> Because I am parsing the string "as I go", I am getting incorrect 

>> results. Not just 8 iunstead of 5, I am getting wierd numbers. It also 

>> does not account for numbers greater than 1 digit in length. Hopefully 

>> someone else can make the necessary corrections/modifications. I simply 

>> don't understand enough to do it right.

>>

>> Wayne

>>

>> PROCEDURE eval

>> DIM a,b,c,d,e,f:INTEGER

>> DIM mul,div,add,sub:BOOLEAN

>> DIM inputStr:STRING

>> a:=0 \b:=0 \c:=0 \d:=0 \e:=0 \f:=0

>> mul:=FALSE \div:=FALSE \add:=FALSE \sub:=FALSE

>> inputStr:="2*3+5/2"

>> REM a:=(2*3+5)/2

>> FOR b:=1 TO LEN(inputStr)

>>  IF MID$(inputStr,b,1)>="0" AND MID$(inputStr,b,1)<="9" THEN

>>    IF c=0 THEN

>>      c:=VAL(MID$(inputStr,b,1))

>>    ELSE IF d=0 THEN

>>      d:=VAL(MID$(inputStr,b,1))

>>      GOSUB 10

>>    ELSE IF e=0 THEN

>>      e:=VAL(MID$(inputStr,b,1))

>>      GOSUB 10

>>    ELSE IF f=0 THEN

>>      f:=VAL(MID$(inputStr,b,1))

>>      GOSUB 10

>>    ENDIF \ENDIF \ENDIF \ENDIF

>>  ELSE

>>    IF MID$(inputStr,b,1)="*" THEN

>>      mul:=TRUE

>>    ELSE IF MID$(inputStr,b,1)="/" THEN

>>      div:=TRUE

>>    ELSE IF MID$(inputStr,b,1)="+" THEN

>>      add:=TRUE

>>    ELSE IF MID$(inputStr,b,1)="-" THEN

>>      sub:=TRUE

>>    ENDIF \ENDIF \ENDIF \ENDIF

>>  ENDIF

>> NEXT b

>> PRINT a

>> END

>> 10 IF mul THEN

>>  a:=a+c*d

>>  mul:=FALSE

>> ELSE IF div THEN

>>  a:=a/e

>>  div:=FALSE

>> ELSE IF add THEN

>>  a:=a+f

>>  add:=FALSE

>> ENDIF \ENDIF \ENDIF

>> RETURN

>>

>> ----- Original Message ----- From: "Christian Lesage" 

>> <hyperfrog at gmail.com>

>> To: "CoCoList for Color Computer Enthusiasts" <coco at maltedmedia.com>

>> Sent: Wednesday, December 30, 2009 7:44 AM

>> Subject: Re: [Coco] The Coco's first webserver, written in Basic09

>>

>>

>>> If BASIC09 has an EVAL statement (I can't remember), you could easily 

>>> program an ASP-like server. That would be pretty cool. I did that using 

>>> another BASIC-like language a few years ago. I started from scratch, and 

>>> the server was small, but good enough for small projects.

>>>

>>> Christian

>>>

>>>

>>> -- 

>>> Coco mailing list

>>> Coco at maltedmedia.com

>>> http://five.pairlist.net/mailman/listinfo/coco

>>

>>

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>

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