evaluation.md

Evaluation

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Add a method def eval(self, variables) to every AST node and recursively call eval until you reach the terminal leaves.

For now we will disregard all runtime errors.

Value

class Value(AST):
    ...
    def eval(self, variables):
        return self.value

Variable

class Variable(AST):
    ...
    def eval(self, variables):
        return variables[self.name]

FuncCall

class FuncCall(AST):
    ...
    def eval(self, variables):
        args = [arg.eval(variables) for arg in self.args]
        return variables[self.name](args)

BinaryOp

class BinaryOp(AST):
    ...
    def eval(self, variables):
        left = self.left.eval(variables)
        right = self.right.eval(variables)
        if self.op == '+':
            return left + right
        if self.op == '-':
            return left - right
        if self.op == '*':
            return left * right
        if self.op == '/':
            return left / right
        if self.op == '%':
            return left % right

UnaryOp

class UnaryOp(AST):
    ...
    def eval(self, variables):
        item = self.item.eval(variables)
        if self.op == '+':
            return +item # redundant, but ey why not
        if self.op == '-':
            return -item

And we are done!

%>py main.py
2.2704074859237844

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