A tiny evaluator of scheme expressions
expression
- define-expr
define "{"
var value-expr |
proc"(" [arg,] ")"
"{"
expr [, expr]
"}"
"}"
- assign-expr
set var value-expr
- if-expr
if predict-expr
"{"
expr [, expr]
"}"
- lambda-expr
lambda"("[arg,] ")" "{" expr [,expr] "}" ["(" [,para] ")"]
- application-expr
proc-name"("[,para]")"
- perform-expr
perform application-expr
Remark
Core of evaluator is interleaving of eval and apply loop. Everytime eval enconters a
application it call apply to make actually calling.
A compound procedure is a sequence of expression to be evaluated
within a given environment.
Example
compute fibonacci with evaluator:
Eval-go INPUT:
define fib(n) {
if ==(n, 0) {0}
if ==(n, 1) {1}
+(fib(-(n,1)), fib(-(n,2)))
};
Eval-go INPUT:
fib(10);
Eval-go OUTPUT:
55