[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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