Demonstrate a simple AST with Python (abstract syntax tree)

If the ' A + 3 * b ' is interpreted, the a=2,b=5

The code is so easy that it is no longer a specific explanation.

Num = Lambda env, N:nvar = lambda env, X:env[x]add = Lambda env, A, b:_eval (env, a) + _eval (env, b) Mul = Lambda env, A, B:_eval (env, a) * _eval (env, b) _eval = Lambda env, expr:expr[0] (env, *expr[1:]) env = {' A ': 2, ' B ': 5}tree = (ADD, (Var, ' a ') ,             (Mul, (Num, 3),                   (Var, ' B '))) print _eval (env, tree)

Output is 17

Demonstrate a simple AST with Python (abstract syntax tree)