fstep
This is my learning python project, mock up pku-minic/first-step with python.
instal
$ pip install fstep
example
# calculate the nth term of the Fibonacci sequence
fib(n) {
if n <= 2 {
return 1
}
else {
return fib(n - 1) + fib(n - 2)
}
}
main() {
print(fib(input()))
return 0
}
You can evaluate this program using the interpreter by running:
$ fstep -s examples/fib.fstep -i
20
6765
0
Or compile it to RISC-V assembly:
$ fstep -s examples/fib.fstep -a
EBNF of first-step
Program ::= {FunctionDef};
FunctionDef ::= IDENT "(" [ArgsDef] ")" Block;
ArgsDef ::= IDENT {"," IDENT};
Block ::= "{" {Statement} "}";
Statement ::= IDENT ":=" Expression
| IDENT "=" Expression
| FunctionCall
| IfElse
| "return" Expression;
IfElse ::= "if" Expression Block ["else" (IfElse | Block)];
Expression ::= LOrExpr;
LOrExpr ::= LAndExpr {"||" LAndExpr};
LAndExpr ::= EqExpr {"&&" EqExpr};
EqExpr ::= RelExpr {("==" | "!=") RelExpr};
RelExpr ::= AddExpr {("<" | "<=") AddExpr};
AddExpr ::= MulExpr {("+" | "-") MulExpr};
MulExpr ::= UnaryExpr {("*" | "/" | "%") UnaryExpr};
UnaryExpr ::= ["-" | "!"] Value;
Value ::= INTEGER
| IDENT
| FunctionCall
| "(" Expression ")";
FunctionCall ::= IDENT "(" [Args] ")";
Args ::= Expression {"," Expression};
