There are many great tutorials about this subject on the internet written by clever people. Maybe my post will not be as great as them or academic style like them but i will always try to keep it simple as possible as. KISS
In this post we are adding basic arithmetic to our interpreter.
class Interpreter:
def __init__(self):
pass
def run(self,code):
for xs in code:
self.eval(xs)
def eval(self,xs):
if isinstance(xs,list):
return self.__getattribute__(xs[0])(xs)
return xs
def Print(self,xs):
if len(xs)==1:
print()
return
l=len(xs)-1
for i,x in enumerate(xs[1:]):
e=self.eval(x)
if i<l-1:
print(e,end="")
else:
if e!=",":
print(e)
else:
print(e,end="")
# Basic arithmetic operations,
# Notice how we call self.eval function recursively:
def Add(self,xs):
return self.eval(xs[1])+self.eval(xs[2])
def Sub(self,xs):
return self.eval(xs[1])-self.eval(xs[2])
def Mul(self,xs):
return self.eval(xs[1])*self.eval(xs[2])
def Div(self,xs):
return self.eval(xs[1])/self.eval(xs[2])
code=[
["Print","3 + 5 = ", ["Add", 3, 5] ],
["Print","1 - 2 * 3 = ", ["Sub", 1, ["Mul", 2, 3] ] ],
["Print",["Add", "Hello ", "again "],"W",["Mul","o",10],"rld!"],
]
interpreter=Interpreter()
interpreter.run(code)
Output:
3 + 5 = 8
1 - 2 * 3 = -5
Hello again Woooooooooorld!
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