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Ingy döt Net 2023-07-01 11:58:00 -04:00
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Task/Arithmetic-evaluation/Liberty-BASIC/arithmetic-evaluation.basic Normal file
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'[RC] Arithmetic evaluation.bas
'Buld the tree (with linked nodes, in array 'cause LB has no pointers)
'applying shunting yard algorythm.
'Then evaluate tree
global stack$ 'operator/brakets stack
stack$=""
maxStack = 100
dim stack(maxStack) 'nodes stack
global SP 'stack pointer
SP = 0
'-------------------
global maxNode,curFree
global FirstOp,SecondOp,isNumber,NodeCont
global opList$
opList$ = "+-*/^"
maxNode=100
FirstOp=1 'pointers to other nodes; 0 means no pointer
SecondOp=2
isNumber=3 'like, 1 is number, 0 is operator
NodeCont=4 'number if isNumber; or mid$("+-*/^", i, 1) for 1..5 operator
dim node(NodeCont, maxNode)
'will be used from 1, 0 plays null pointer (no link)
curFree=1 'first free node
'-------------------
in$ = " 1 + 2 ^ 3 * 4 - 12 / 6 "
print "Input: "
print in$
'read tokens
token$ = "#"
while 1
i=i+1
token$ = word$(in$, i)
if token$ = "" then i=i-1: exit while
select case
case token$ = "("
'If the token is a left parenthesis, then push it onto the stack.
call stack.push token$
case token$ = ")"
'If the token is a right parenthesis:
'Until the token at the top of the stack is a left parenthesis, pop operators off the stack onto the output queue.
'Pop the left parenthesis from the stack, but not onto the output queue.
'If the stack runs out without finding a left parenthesis, then there are mismatched parentheses.
while stack.peek$() <> "("
'if stack is empty
if stack$="" then print "Error: no matching '(' for token ";i: end
'add operator node to tree
child2=node.pop()
child1=node.pop()
call node.push addOpNode(child1,child2,stack.pop$())
wend
discard$=stack.pop$() 'discard "("
case isOperator(token$)
'If the token is an operator, o1, then:
'while there is an operator token, o2, at the top of the stack, and
'either o1 is left-associative and its precedence is equal to that of o2,
'or o1 has precedence less than that of o2,
' pop o2 off the stack, onto the output queue;
'push o1 onto the stack
op1$=token$
while(isOperator(stack.peek$()))
op2$=stack.peek$()
if (op2$<>"^" and precedence(op1$) = precedence(op2$)) _
OR (precedence(op1$) < precedence(op2$)) then
'"^" is the only right-associative operator
'add operator node to tree
child2=node.pop()
child1=node.pop()
call node.push addOpNode(child1,child2,stack.pop$())
else
exit while
end if
wend
call stack.push op1$
case else 'number
'actually, wrohg operator could end up here, like say %
'If the token is a number, then
'add leaf node to tree (number)
call node.push addNumNode(val(token$))
end select
wend
'When there are no more tokens to read:
'While there are still operator tokens in the stack:
' If the operator token on the top of the stack is a parenthesis, then there are mismatched parentheses.
' Pop the operator onto the output queue.
while stack$<>""
if stack.peek$() = "(" then print "no matching ')'": end
'add operator node to tree
child2=node.pop()
child1=node.pop()
call node.push addOpNode(child1,child2,stack.pop$())
wend
root = node.pop()
'call dumpNodes
print "Tree:"
call drawTree root, 1, 0, 3
locate 1, 10
print "Result: ";evaluate(root)
end
'------------------------------------------
function isOperator(op$)
isOperator = instr(opList$, op$)<>0 AND len(op$)=1
end function
function precedence(op$)
if isOperator(op$) then
precedence = 1 _
+ (instr("+-*/^", op$)<>0) _
+ (instr("*/^", op$)<>0) _
+ (instr("^", op$)<>0)
end if
end function
'------------------------------------------
sub stack.push s$
stack$=s$+"|"+stack$
end sub
function stack.pop$()
'it does return empty on empty stack or queue
stack.pop$=word$(stack$,1,"|")
stack$=mid$(stack$,instr(stack$,"|")+1)
end function
function stack.peek$()
'it does return empty on empty stack or queue
stack.peek$=word$(stack$,1,"|")
end function
'---------------------------------------
sub node.push s
stack(SP)=s
SP=SP+1
end sub
function node.pop()
'it does return -999999 on empty stack
if SP<1 then pop=-999999: exit function
SP=SP-1
node.pop=stack(SP)
end function
'=======================================
sub dumpNodes
for i = 1 to curFree-1
print i,
for j = 1 to 4
print node(j, i),
next
print
next
print
end sub
function evaluate(node)
if node=0 then exit function
if node(isNumber, node) then
evaluate = node(NodeCont, node)
exit function
end if
'else operator
op1 = evaluate(node(FirstOp, node))
op2 = evaluate(node(SecondOp, node))
select case node(NodeCont, node) 'opList$, "+-*/^"
case 1
evaluate = op1+op2
case 2
evaluate = op1-op2
case 3
evaluate = op1*op2
case 4
evaluate = op1/op2
case 5
evaluate = op1^op2
end select
end function
sub drawTree node, level, leftRight, offsetY
if node=0 then exit sub
call drawTree node(FirstOp, node), level+1, leftRight-1/2^level, offsetY
'print node
'count on 80 char maiwin
x = 40*(1+leftRight)
y = level+offsetY
locate x, y
'print x, y,">";
if node(isNumber, node) then
print node(NodeCont, node)
else
print mid$(opList$, node(NodeCont, node),1)
end if
call drawTree node(SecondOp, node), level+1, leftRight+1/2^level, offsetY
end sub
function addNumNode(num)
'returns new node
newNode=curFree
curFree=curFree+1
node(isNumber,newNode)=1
node(NodeCont,newNode)=num
addNumNode = newNode
end function
function addOpNode(firstChild, secondChild, op$)
'returns new node
'FirstOrSecond ignored if parent is 0
newNode=curFree
curFree=curFree+1
node(isNumber,newNode)=0
node(NodeCont,newNode)=instr(opList$, op$)
node(FirstOp,newNode)=firstChild
node(SecondOp,newNode)=secondChild
addOpNode = newNode
end function