interpreter

[NewMan]

i was trying to create a scripting lang. i have searched the forum but did not get what i really wanted. i know how to execute functions like messagebox by getting their args etc. the only thing i was thinking how to do is assigning variables. for example user writes declare a long(or whatever) my program can catch that declare and know that user is trying to delcare a varible, but how do i create a variable with the provided name and type and if user further types a = 20 then how do i assign the value to the correct variable?

[jack]

viewtopic.php?t=10001

[LarsG]

You might want to check out this one:
http://compilers.iecc.com/crenshaw/

it shows you basically how to build a compiler from scratch..
allthough the source is originally made in Pascal, and the assembler
output is in 68K (IIRC), you can fairly easy convert it to PB and x86 ASM.

I have been following some chapters, and I've got a nice little parser,
handling complex math instructions and variable assignment..
I just wish my x86 ASM was better.. hehe

[edit]
I didn't see that the thread was about interpreters.. lol
but the link is still valid, as Crenshaw covers the basic interpreting as well..
[/edit]

[patrick88]

this example code is getting from example code of smallbasic
it is writing with the langage smallbasic...

another basic is ddsbasic finding on web or in linux distrib ... it's writing in c an is it small (5kb) easy to traduc in pb

excuse my bad english, i'm french

patrick

Code: Select all

' TinyBASIC, by Nicholas Christopoulos
' A SmallBASIC example :)

DIM variables(26)	' variables (one for each letter)
DIM stack(10)		' executor's stack (GOSUB/FOR-NEXT/WHILE-WEND)
DIM labels(), program()

DEF varidx(name) = asc(left(name))-65

ip = -1	' next command to execute (-1 = none, -2 = error)
sp = 0	' stack pointer

CLS
print cat(2);"TinyBASIC v1";cat(-2)
print "A 450-line (with expression parser) SmallBASIC example"
print
print "Type HELP for catalog."
print "Type QUIT to exit..."
print 
print "READY"
print

repeat
	input "> ", inpstr
	inpstr = trim(upper(inpstr))
	cmd = trim(leftof(inpstr+" ", " "))		' get command name
	if len(cmd)
		par = trim(rightof(inpstr, " "))
		if isnumber(cmd)					' store command
			addcmd val(cmd), par
		else								' execute command
			execute cmd, par
		fi
	fi
until cmd="QUIT"
end

' Store command to memory
sub addcmd(num, cmd)
local i, ins, rep

ins = len(labels): rep = -1
for i = 0 to len(labels)-1
	if labels(i) = num then rep=i:exit
	if labels(i) > num then ins=i:exit
next
if rep = -1			' new record
	if len(cmd)		' no error, insert (or append)
		insert labels, ins, num
		insert program, ins, cmd
	fi
else			
	if len(cmd)		' replace
		program(rep) = cmd
	else			' erase
		delete labels, rep
		delete program, rep
	fi
fi
end

' set value to a variable
sub setvar(varname, varval)
local	idx

if len(varname)>1
	TBError "ILLEGAL VARIABLES NAME, USE ONE-CHAR NAMES"
else
	idx = varidx(varname)
	varval = trim(varval)
	if left(varvar) = chr(34) ' it is a string
		variables(idx) = disclose(varval)
	else	' it is an expression
		variables(idx) = tbeval(varval)
	fi
fi
end

' execute a TB command
sub execute(cmd, par)
local idx, i, var, vstr
local parA, tstr, fstr, f, num

if cmd in ["END", "NEW"]
	' new program or end of program; syntax: NEW or END
	ip = -1
	sp = 0
	if cmd="NEW"
		erase labels, commands ' clear program
		dim variables(26) ' clear variables
		print:print "* DONE *":print
	fi
elif cmd in ["QUIT", "REM"]
	' do nothing
elif cmd="LET"
	' assigns a value to a variable; syntax: LET variable = expression
	sinput par; var, "=", vstr
	setvar var, vstr
elif cmd="LIST"
	' prints the program, syntax: LIST
	if len(labels) 
		for i=0 to len(labels)-1
			print using "####: &"; labels(i); program(i)
		next
	else
		TBError "NO PROGRAM IN MEMORY"
	fi
elif cmd="RUN"
	' run the program, syntax: RUN
	ip = 0
	while ip<len(labels)
		last_ip = ip

		cmd = trim(leftof(program(ip)+" ", " "))
		par = trim(rightof(program(ip), " "))
		execute cmd, par

		if ip = -2
			print "* ERROR AT ";labels(last_ip);" *"
			sp = 0
			exit
		elif ip = -1
			print:print "* DONE *":print
			sp = 0
			exit
		else
			ip = ip + 1
		fi
	wend
elif cmd="INPUT"
	' get a value form console, syntax: INPUT [prompt,] variable
	split par, ",", para, chr(34)+chr(34) use trim(x)
	if len(para) = 0
		ip = -2
	else
		if len(para) = 2
			idx = 1
			input disclose(para(i)); vstr
		else
			idx = 0
			input "? ", vstr
		fi
		setvar para(idx), vstr
	fi
elif cmd="PRINT"
	' print to console, syntax: PRINT [var1 [, varN]]
	split par, ",", para, chr(34)+chr(34)+"()" use trim(x)
	for vstr in para
		if left(vstr)=chr(34)		' print string
			print disclose(vstr); " ";
		else						' print number (expression)
			print tbeval(vstr); " ";
		fi
	next
	print
elif cmd in ["GOTO", "GOSUB"]
	' Syntax: GOTO line or GOSUB line
	search labels, val(par), idx
	if idx = -1
		TBError "LABEL "+par+" DOES NOT EXIST"
	else
		if cmd="GOSUB"
			stack(sp) = ["R", ip]	' "R" = a 'return' command  must read it
			sp = sp + 1
		fi
		ip = idx-1
	fi
elif cmd="RETURN"
	' syntax: RETURN
	if sp > 0
		sp = sp - 1
		if stack(sp)(0) = "R"	' later you can add code for FOR and WHILE 
			ip = stack(sp)(1)
		else
			TBError "STACK MESS"
		fi
	else
		TBError "STACK UNDERFLOW"
	fi
elif cmd="IF"
	' IF! what else?. Syntax: IF expression THEN line [ ELSE line ] 
	sinput par; vstr, " THEN ", tstr, " ELSE ", fstr
	if tbeval(vstr)
		execute "GOTO",tstr
	elif len(fstr)
		execute "GOTO",fstr
	fi
elif cmd="SAVE"
	f=disclose(par)
	if len(f)=0
		TBError "MISSING: FILENAME"
	else
		if isarray(labels) 
		if instr(f, ".TBAS")=0 THEN f=f+".tbas" ELSE f=leftoflast(f, ".TBAS")+".tbas"
			open f for output as #1
			for i=0 to len(labels)-1
				print #1; labels(i); " "; program(i)
			next
			close #1
			print:print "* DONE *":print
		else
			TBError "NO PROGRAM IN MEMORY"
		fi
	fi
elif cmd="LOAD"
	f=disclose(par)
	if len(f)=0
		TBError "MISSING: FILENAME"
	else
		ip = -1
		sp = 0
		erase labels, commands ' clear program
		dim variables(26) ' clear variables
		if instr(f, ".TBAS")=0 THEN f=f+".tbas" ELSE f=leftoflast(f, ".TBAS")+".tbas"
		open f for input as #1
		while not eof(1)
			line input #1; vstr
			num  = leftof (vstr, " ")
			par  = rightof(vstr, " ")
			addcmd val(num), par
		wend
		close #1
		print:print "* DONE *":print
	fi
elif cmd="FILES"
	print files("*.tbas")
elif cmd="HELP"
	PRINT
	print "  ";cat(2);"TinyBASIC, v1";cat(-2)
	PRINT
	print "  * All variables are real numbers."
	print "  * There are 26 variables, one for each letter"
	print "  * INPUT return real number (not string)"
	print "  * IF-THEN accepts only line-numbers (IF x THEN line ELSE line)"
	print "  * PRINT uses only , as separator"
	PRINT
	print "  HELP";tab(15);"This screen"
	print "  NEW";tab(15);"New program"
	print "  RUN";tab(15);"Run program"
	print "  LIST";tab(15);"Prints program to screen"
	print "  SAVE";tab(15);"Saves program to disk"
	print "  LOAD";tab(15);"Loads a program from disk"
	print "  FILES";tab(15);"Prints the list of TB programs"
	print "  REM";tab(15);"Remarks"
	print "  GOTO";tab(15);"Transfers control to ..."
	print "  LET";tab(15);"Assigns a value to a variable"
	print "  PRINT";tab(15);"Prints an expression"
	print "  INPUT";tab(15);"Inputs a value"
	print "  IF";tab(15);" "
	print "  GOSUB";tab(15);" "
	print "  RETURN";tab(15);" "
	print "  END";tab(15);"Terminate the program"
	PRINT
else
	TBError "BAD COMMAND"
fi
end

' Run-time error
sub TBError(errmsg)
PRINT
print chr(7);"* ";errmsg;" *"
PRINT
ip = -2
end

' ==== expression parser ====

' evaluate an expression
def TBEval(expr)
local result, rmn, c

result = 0
expr = ltrim(expr)
if len(expr) then logical result, expr
TBEval = result
end

' number
def valueof(byref expr)
local c, i, v

for i=1 to len(expr)
	c = mid(expr, i, 1)
	if not (c in "0123456789.") then exit
next
if i < len(expr)
	v = left(expr, i-1)
	expr = mid(expr, i)
else
	v = expr
	expr = ""
fi
valueof = val(v)
end

' operators: ( ) or value
sub parenth(byref l, byref expr)
local	op, vname

op = left(expr)
if op = "("
	expr = mid(expr, 2)
	logical l, expr
	if left(expr)=")" then expr = mid(expr, 2)
else
	if op in "0123456789."
		l = valueof(expr)
	' elif, check for function
	else ' variable
		l = variables(varidx(expr))
		expr = if(len(expr)>1, mid(expr, 2), "")
	fi
fi
end

' unary operators: - + NOT
sub unary(byref l, byref expr)
local op

if left(expr,3) = "NOT"
	op="NOT"
	expr = mid(expr,4)
elif left(expr,1) in ["-", "+"]
	op=left(expr)
	expr=mid(expr,2)
fi
parenth l, expr
if op="NOT"
	l = NOT l
elif op="-"
	l = -l
elif op="+"
	' ignore it
fi
end

' operators: * /
sub muldiv(byref l, byref expr)
local	op, r

unary l, expr
while left(expr) in "*/"
	op = left(expr)
	expr = mid(expr, 2)
	unary r, expr
	if op = "*"
		l *= r
	elif op = "/"
		if r=0 
			TBError "DIVISION BY ZERO" 
		else
			l /= r
		fi
	fi
wend
end

' operators: + -
sub addsub(byref l, byref expr)
local	op, r

muldiv l, expr
while left(expr) in "+-"
	op = left(expr)
	expr = mid(expr, 2)
	muldiv r, expr
	if op = "+" 
		l += r
	elif op = "-"
		l -= r
	fi
wend
end

' returns the logical operator
func getlogopr(expr)
local	idx, op3, op2, op1

op3=["AND"]
op2=["OR", "<=", ">=", "=<", "=>", "<>"]
op1=["=", ">", "<"]
search op3, left(expr,3), idx
if idx >= 0 then getlogopr=op3(idx):exit
search op2, left(expr,2), idx
if idx >= 0 then getlogopr=op2(idx):exit
search op1, left(expr,1), idx
if idx >= 0 then getlogopr=op1(idx):exit
getlogopr=""
end

' logical and comparation operators
sub logical(byref l, byref expr)
local	op, r

addsub l, expr
while getlogopr(expr) <> ""
	op = getlogopr(expr)
	expr = mid(expr, len(op)+1)
	addsub r, expr
	if op = "AND"
		l = l AND r
	elif op = "OR"
		l = l OR r
	elif op = "="
		l = (l = r)
	elif op = "<"
		l = l < r
	elif op = ">"
		l = l > r
	elif op = ">=" or op = "=>"
		l = l >= r
	elif op = "<=" or op = "=<"
		l = l <= r
	elif op = "<>"
		l = l <> r
	fi
wend
end