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Add support for functions declared in script

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This commit is contained in:
jonathandturner 2016-03-01 20:45:02 -05:00
parent a8fa76c2fc
commit d8dd673459
3 changed files with 236 additions and 116 deletions
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315
src/engine.rs
View File

@ -4,7 +4,7 @@ use std::any::Any;
use std::boxed::Box;
use std::fmt;
use parser::{lex, parse, Expr, Stmt };
use parser::{lex, parse, Expr, Stmt, FnDef };
use fn_register::FnRegister;
use std::ops::{Add, Sub, Mul, Div};
@ -16,7 +16,8 @@ pub enum EvalError {
FunctionArgMismatch,
FunctionCallNotSupported,
IfGuardMismatch,
VariableNotFound
VariableNotFound,
FunctionArityNotSupported
}
impl Error for EvalError {
@ -27,6 +28,7 @@ impl Error for EvalError {
EvalError::FunctionCallNotSupported => "Function call with > 2 argument not supported",
EvalError::IfGuardMismatch => "If guards expect boolean expression",
EvalError::VariableNotFound => "Variable not found",
EvalError::FunctionArityNotSupported => "Functions of more than 3 parameters are not yet supported"
}
}
@ -89,23 +91,52 @@ fn or(x: bool, y: bool) -> bool {
x || y
}
pub struct Engine {
pub fns_arity_3: HashMap<String, Vec<Box<Fn(&mut Box<Any>, &mut Box<Any>, &mut Box<Any>)->Result<Box<Any>, EvalError>>>>,
pub fns_arity_2: HashMap<String, Vec<Box<Fn(&mut Box<Any>, &mut Box<Any>)->Result<Box<Any>, EvalError>>>>,
pub fns_arity_1: HashMap<String, Vec<Box<Fn(&mut Box<Any>)->Result<Box<Any>, EvalError>>>>,
pub fns_arity_0: HashMap<String, Vec<Box<Fn()->Result<Box<Any>, EvalError>>>>,
pub scope: Vec<(String, Box<Any>)>
pub enum Arity3 {
ExternalFn(Box<Fn(&mut Box<Any>, &mut Box<Any>, &mut Box<Any>)->Result<Box<Any>, EvalError>>),
InternalFn(FnDef)
}
pub enum Arity2 {
ExternalFn(Box<Fn(&mut Box<Any>, &mut Box<Any>)->Result<Box<Any>, EvalError>>),
InternalFn(FnDef)
}
pub enum Arity1 {
ExternalFn(Box<Fn(&mut Box<Any>)->Result<Box<Any>, EvalError>>),
InternalFn(FnDef)
}
pub enum Arity0 {
ExternalFn(Box<Fn()->Result<Box<Any>, EvalError>>),
InternalFn(FnDef)
}
pub struct Engine {
pub fns_arity_3: HashMap<String, Vec<Arity3>>,
pub fns_arity_2: HashMap<String, Vec<Arity2>>,
pub fns_arity_1: HashMap<String, Vec<Arity1>>,
pub fns_arity_0: HashMap<String, Vec<Arity0>>,
}
pub type Scope = Vec<(String, Box<Any>)>;
impl Engine {
pub fn call_fn_0_arg(fns_arity_0: &HashMap<String, Vec<Box<Fn()->Result<Box<Any>, EvalError>>>>, name: &str) -> Result<Box<Any>, EvalError> {
match fns_arity_0.get(name) {
fn call_fn_0_arg(&self, name: &str) -> Result<Box<Any>, EvalError> {
match self.fns_arity_0.get(name) {
Some(vf) => {
for f in vf {
let invoke = f();
match invoke {
Ok(v) => return Ok(v),
_ => ()
for arr_f in vf {
match arr_f {
& Arity0::ExternalFn(ref f) => {
let invoke = f();
match invoke {
Ok(v) => return Ok(v),
_ => ()
}
}
& Arity0::InternalFn(ref f) => {
let mut new_scope: Scope = Vec::new();
return self.eval_stmt(&mut new_scope, &*f.body);
}
}
};
Err(EvalError::FunctionArgMismatch)
@ -114,16 +145,27 @@ impl Engine {
}
}
pub fn call_fn_1_arg(fns_arity_1: &HashMap<String, Vec<Box<Fn(&mut Box<Any>)->Result<Box<Any>, EvalError>>>>,
name: &str, arg1: &mut Box<Any>) -> Result<Box<Any>, EvalError> {
match fns_arity_1.get(name) {
fn call_fn_1_arg(&self, name: &str, arg1: &mut Box<Any>) -> Result<Box<Any>, EvalError> {
match self.fns_arity_1.get(name) {
Some(vf) => {
for f in vf {
let invoke = f(arg1);
match invoke {
Ok(v) => return Ok(v),
_ => ()
for arr_f in vf {
match arr_f {
& Arity1::ExternalFn(ref f) => {
let invoke = f(arg1);
match invoke {
Ok(v) => return Ok(v),
_ => ()
}
}
& Arity1::InternalFn(ref f) => {
let mut new_scope: Scope = Vec::new();
let result = self.call_fn_1_arg("clone", arg1);
match result {
Ok(r) => new_scope.push((f.params[0].clone(), r)),
_ => return Err(EvalError::FunctionArgMismatch)
}
return self.eval_stmt(&mut new_scope, &*f.body);
}
}
};
Err(EvalError::FunctionArgMismatch)
@ -132,16 +174,31 @@ impl Engine {
}
}
pub fn call_fn_2_arg(fns_arity_2: &HashMap<String, Vec<Box<Fn(&mut Box<Any>, &mut Box<Any>)->Result<Box<Any>, EvalError>>>>,
name: &str, arg1: &mut Box<Any>, arg2: &mut Box<Any>) -> Result<Box<Any>, EvalError> {
match fns_arity_2.get(name) {
fn call_fn_2_arg(&self, name: &str, arg1: &mut Box<Any>, arg2: &mut Box<Any>) -> Result<Box<Any>, EvalError> {
match self.fns_arity_2.get(name) {
Some(vf) => {
for f in vf {
let invoke = f(arg1, arg2);
match invoke {
Ok(v) => return Ok(v),
_ => ()
for arr_f in vf {
match arr_f {
& Arity2::ExternalFn(ref f) => {
let invoke = f(arg1, arg2);
match invoke {
Ok(v) => return Ok(v),
_ => ()
}
}
& Arity2::InternalFn(ref f) => {
let mut new_scope: Scope = Vec::new();
let result1 = self.call_fn_1_arg("clone", arg1);
let result2 = self.call_fn_1_arg("clone", arg2);
match (result1, result2) {
(Ok(r1), Ok(r2)) => {
new_scope.push((f.params[0].clone(), r1));
new_scope.push((f.params[1].clone(), r2));
},
_ => return Err(EvalError::FunctionArgMismatch)
}
return self.eval_stmt(&mut new_scope, &*f.body);
}
}
};
Err(EvalError::FunctionArgMismatch)
@ -150,16 +207,33 @@ impl Engine {
}
}
pub fn call_fn_3_arg(fns_arity_3: &HashMap<String, Vec<Box<Fn(&mut Box<Any>, &mut Box<Any>, &mut Box<Any>)->Result<Box<Any>, EvalError>>>>,
name: &str, arg1: &mut Box<Any>, arg2: &mut Box<Any>, arg3: &mut Box<Any>) -> Result<Box<Any>, EvalError> {
match fns_arity_3.get(name) {
pub fn call_fn_3_arg(&self, name: &str, arg1: &mut Box<Any>, arg2: &mut Box<Any>, arg3: &mut Box<Any>) -> Result<Box<Any>, EvalError> {
match self.fns_arity_3.get(name) {
Some(vf) => {
for f in vf {
let invoke = f(arg1, arg2, arg3);
match invoke {
Ok(v) => return Ok(v),
_ => ()
for arr_f in vf {
match arr_f {
& Arity3::ExternalFn(ref f) => {
let invoke = f(arg1, arg2, arg3);
match invoke {
Ok(v) => return Ok(v),
_ => ()
}
}
& Arity3::InternalFn(ref f) => {
let mut new_scope: Scope = Vec::new();
let result1 = self.call_fn_1_arg("clone", arg1);
let result2 = self.call_fn_1_arg("clone", arg2);
let result3 = self.call_fn_1_arg("clone", arg3);
match (result1, result2, result3) {
(Ok(r1), Ok(r2), Ok(r3)) => {
new_scope.push((f.params[0].clone(), r1));
new_scope.push((f.params[1].clone(), r2));
new_scope.push((f.params[2].clone(), r3));
},
_ => return Err(EvalError::FunctionArgMismatch)
}
return self.eval_stmt(&mut new_scope, &*f.body);
}
}
};
Err(EvalError::FunctionArgMismatch)
@ -174,14 +248,15 @@ impl Engine {
&(clone_helper as fn(T)->T).register(self, "clone");
}
fn eval_expr(&mut self, expr: &Expr) -> Result<Box<Any>, EvalError> {
fn eval_expr(&self, scope: &mut Scope, expr: &Expr) -> Result<Box<Any>, EvalError> {
match *expr {
Expr::IntConst(i) => Ok(Box::new(i)),
Expr::Identifier(ref id) => {
for &mut (ref name, ref mut val) in &mut self.scope.iter_mut().rev() {
for &mut (ref name, ref mut val) in &mut scope.iter_mut().rev() {
if *id == *name {
//Ideally, we wouldn't have to inline this call above
//let result = self.call_fn_1_arg("clone", val);
let result = self.call_fn_1_arg("clone", val);
/*
let result = match self.fns_arity_1.get("clone") {
Some(vf) => {
for f in vf {
@ -195,7 +270,7 @@ impl Engine {
}
None => Err(EvalError::FunctionNotFound)
};
*/
return result;
}
}
@ -204,8 +279,8 @@ impl Engine {
Expr::Assignment(ref id, ref rhs) => {
match **id {
Expr::Identifier(ref n) => {
let rhs_val = try!(self.eval_expr(rhs));
for &mut (ref name, ref mut val) in &mut self.scope.iter_mut().rev() {
let rhs_val = try!(self.eval_expr(scope, rhs));
for &mut (ref name, ref mut val) in &mut scope.iter_mut().rev() {
if *n == *name {
*val = rhs_val;
@ -220,25 +295,25 @@ impl Engine {
}
Expr::FnCall(ref fn_name, ref args) => {
if args.len() == 0 {
Engine::call_fn_0_arg(&self.fns_arity_0, &fn_name)
self.call_fn_0_arg(&fn_name)
}
else if args.len() == 1 {
let mut arg = try!(self.eval_expr(&args[0]));
let mut arg = try!(self.eval_expr(scope, &args[0]));
Engine::call_fn_1_arg(&self.fns_arity_1, &fn_name, &mut arg)
self.call_fn_1_arg(&fn_name, &mut arg)
}
else if args.len() == 2 {
let mut arg1 = try!(self.eval_expr(&args[0]));
let mut arg2 = try!(self.eval_expr(&args[1]));
let mut arg1 = try!(self.eval_expr(scope, &args[0]));
let mut arg2 = try!(self.eval_expr(scope, &args[1]));
Engine::call_fn_2_arg(&self.fns_arity_2, &fn_name, &mut arg1, &mut arg2)
self.call_fn_2_arg(&fn_name, &mut arg1, &mut arg2)
}
else if args.len() == 3 {
let mut arg1 = try!(self.eval_expr(&args[0]));
let mut arg2 = try!(self.eval_expr(&args[1]));
let mut arg3 = try!(self.eval_expr(&args[1]));
let mut arg1 = try!(self.eval_expr(scope, &args[0]));
let mut arg2 = try!(self.eval_expr(scope, &args[1]));
let mut arg3 = try!(self.eval_expr(scope, &args[1]));
Engine::call_fn_3_arg(&self.fns_arity_3, &fn_name, &mut arg1, &mut arg2, &mut arg3)
self.call_fn_3_arg(&fn_name, &mut arg1, &mut arg2, &mut arg3)
}
else {
Err(EvalError::FunctionCallNotSupported)
@ -246,30 +321,30 @@ impl Engine {
}
Expr::MethodCall(ref target, ref fn_name, ref args) => {
if args.len() == 0 {
for &mut (ref name, ref mut val) in &mut self.scope.iter_mut().rev() {
for &mut (ref name, ref mut val) in &mut scope.iter_mut().rev() {
if *target == *name {
return Engine::call_fn_1_arg(&self.fns_arity_1, &fn_name, val);
return self.call_fn_1_arg(&fn_name, val);
}
}
Err(EvalError::VariableNotFound)
}
else if args.len() == 1 {
let mut arg = try!(self.eval_expr(&args[0]));
let mut arg = try!(self.eval_expr(scope, &args[0]));
for &mut (ref name, ref mut val) in &mut self.scope.iter_mut().rev() {
for &mut (ref name, ref mut val) in &mut scope.iter_mut().rev() {
if *target == *name {
return Engine::call_fn_2_arg(&self.fns_arity_2, &fn_name, val, &mut arg);
return self.call_fn_2_arg(&fn_name, val, &mut arg);
}
}
Err(EvalError::VariableNotFound)
}
else if args.len() == 2 {
let mut arg1 = try!(self.eval_expr(&args[0]));
let mut arg2 = try!(self.eval_expr(&args[1]));
let mut arg1 = try!(self.eval_expr(scope, &args[0]));
let mut arg2 = try!(self.eval_expr(scope, &args[1]));
for &mut (ref name, ref mut val) in &mut self.scope.iter_mut().rev() {
for &mut (ref name, ref mut val) in &mut scope.iter_mut().rev() {
if *target == *name {
return Engine::call_fn_3_arg(&self.fns_arity_3, &fn_name, val, &mut arg1, &mut arg2);
return self.call_fn_3_arg(&fn_name, val, &mut arg1, &mut arg2);
}
}
Err(EvalError::VariableNotFound)
@ -287,31 +362,31 @@ impl Engine {
}
}
fn eval_stmt(&mut self, stmt: &Stmt) -> Result<Box<Any>, EvalError> {
fn eval_stmt(&self, scope: &mut Scope, stmt: &Stmt) -> Result<Box<Any>, EvalError> {
match *stmt {
Stmt::Expr(ref e) => {
self.eval_expr(e)
self.eval_expr(scope, e)
}
Stmt::Block(ref b) => {
let prev_len = self.scope.len();
let prev_len = scope.len();
let mut last_result : Result<Box<Any>, EvalError> = Ok(Box::new(0));
for s in b.iter() {
last_result = self.eval_stmt(s)
last_result = self.eval_stmt(scope, s)
}
while self.scope.len() > prev_len {
self.scope.pop();
while scope.len() > prev_len {
scope.pop();
}
return last_result;
}
Stmt::If(ref guard, ref body) => {
let guard_result = try!(self.eval_expr(guard));
let guard_result = try!(self.eval_expr(scope, guard));
match guard_result.downcast::<bool>() {
Ok(g) => {
if *g {
self.eval_stmt(body)
self.eval_stmt(scope, body)
}
else {
Ok(Box::new(()))
@ -322,11 +397,11 @@ impl Engine {
}
Stmt::While(ref guard, ref body) => {
loop {
let guard_result = try!(self.eval_expr(guard));
let guard_result = try!(self.eval_expr(scope, guard));
match guard_result.downcast::<bool>() {
Ok(g) => {
if *g {
try!(self.eval_stmt(body));
try!(self.eval_stmt(scope, body));
}
else {
return Ok(Box::new(()));
@ -339,11 +414,11 @@ impl Engine {
Stmt::Var(ref name, ref init) => {
match init {
& Some(ref v) => {
let i = try!(self.eval_expr(v));
self.scope.push((name.clone(), i));
let i = try!(self.eval_expr(scope, v));
scope.push((name.clone(), i));
},
& None => {
self.scope.push((name.clone(), Box::new(())));
scope.push((name.clone(), Box::new(())));
}
};
Ok(Box::new(()))
@ -352,6 +427,12 @@ impl Engine {
}
pub fn eval(&mut self, input: String) -> Result<Box<Any>, EvalError> {
let mut scope: Scope = Vec::new();
self.eval_with_scope(&mut scope, input)
}
pub fn eval_with_scope(&mut self, scope: &mut Scope, input: String) -> Result<Box<Any>, EvalError> {
let tokens = lex(&input);
let mut peekables = tokens.peekable();
@ -360,23 +441,43 @@ impl Engine {
match tree {
Ok((ref os, ref fns)) => {
let mut x: Result<Box<Any>, EvalError> = Ok(Box::new(()));
for f in fns {
if f.params.len() == 0 {
let local_f = f.clone();
let ent = self.fns_arity_0.entry(local_f.name).or_insert(Vec::new());
let wrapped : Box<Fn()->Result<Box<Any>, EvalError>> =
Box::new(move || { Ok(Box::new(0)) } );
//move || { self.eval_stmt(&local_f.body) }
(*ent).push(wrapped);
match f.params.len() {
0 => {
let name = f.name.clone();
let local_f = f.clone();
let ent = self.fns_arity_0.entry(name).or_insert(Vec::new());
(*ent).push(Arity0::InternalFn(local_f));
},
1 => {
let name = f.name.clone();
let local_f = f.clone();
let ent = self.fns_arity_1.entry(name).or_insert(Vec::new());
(*ent).push(Arity1::InternalFn(local_f));
},
2 => {
let name = f.name.clone();
let local_f = f.clone();
let ent = self.fns_arity_2.entry(name).or_insert(Vec::new());
(*ent).push(Arity2::InternalFn(local_f));
},
3 => {
let name = f.name.clone();
let local_f = f.clone();
let ent = self.fns_arity_3.entry(name).or_insert(Vec::new());
(*ent).push(Arity3::InternalFn(local_f));
},
_ => return Err(EvalError::FunctionArityNotSupported)
}
}
for o in os {
x = self.eval_stmt(&o)
x = self.eval_stmt(scope, &o);
}
x
}
Err(_) => Err(EvalError::FunctionArgMismatch),
Err(_) => Err(EvalError::FunctionArgMismatch)
}
}
@ -428,8 +529,7 @@ impl Engine {
fns_arity_0: HashMap::new(),
fns_arity_1: HashMap::new(),
fns_arity_2: HashMap::new(),
fns_arity_3: HashMap::new(),
scope: Vec::new()
fns_arity_3: HashMap::new()
};
Engine::register_default_lib(&mut engine);
@ -464,7 +564,7 @@ fn test_addition() {
}
#[test]
fn test_bool_op() {
fn test_bool_op1() {
let mut engine = Engine::new();
if let Ok(result) = engine.eval("true && (false || true)".to_string()).unwrap().downcast::<bool>() {
@ -473,6 +573,11 @@ fn test_bool_op() {
else {
assert!(false);
}
}
#[test]
fn test_bool_op2() {
let mut engine = Engine::new();
if let Ok(result) = engine.eval("false && (false || true)".to_string()).unwrap().downcast::<bool>() {
assert_eq!(*result, false);
@ -507,30 +612,32 @@ fn test_if() {
}
#[test]
fn test_var_scope() {
let mut engine = Engine::new();
let mut scope: Scope = Vec::new();
if let Ok(_) = engine.eval("var x = 4 + 5".to_string()) { } else { assert!(false); }
if let Ok(_) = engine.eval_with_scope(&mut scope, "var x = 4 + 5".to_string()) { } else { assert!(false); }
if let Ok(result) = engine.eval("x".to_string()).unwrap().downcast::<i32>() {
if let Ok(result) = engine.eval_with_scope(&mut scope, "x".to_string()).unwrap().downcast::<i32>() {
assert_eq!(*result, 9);
}
else {
assert!(false);
}
if let Ok(_) = engine.eval("x = x + 1; x = x + 2;".to_string()) { } else { assert!(false); }
if let Ok(_) = engine.eval_with_scope(&mut scope, "x = x + 1; x = x + 2;".to_string()) { } else { assert!(false); }
if let Ok(result) = engine.eval("x".to_string()).unwrap().downcast::<i32>() {
if let Ok(result) = engine.eval_with_scope(&mut scope, "x".to_string()).unwrap().downcast::<i32>() {
assert_eq!(*result, 12);
}
else {
assert!(false);
}
if let Ok(_) = engine.eval("{var x = 3}".to_string()) { } else { assert!(false); }
if let Ok(_) = engine.eval_with_scope(&mut scope, "{var x = 3}".to_string()) { } else { assert!(false); }
if let Ok(result) = engine.eval("x".to_string()).unwrap().downcast::<i32>() {
if let Ok(result) = engine.eval_with_scope(&mut scope, "x".to_string()).unwrap().downcast::<i32>() {
assert_eq!(*result, 12);
}
else {
@ -570,3 +677,15 @@ fn test_method_call() {
}
}
#[test]
fn test_internal_fn() {
let mut engine = Engine::new();
if let Ok(result) = engine.eval( "fn addme(a, b) { a+b } addme(3, 4)".to_string()).unwrap().downcast::<i32>() {
assert_eq!(*result, 7);
}
else {
assert!(false);
}
}

16
src/fn_register.rs
View File

@ -1,7 +1,7 @@
use std::any::Any;
use std::boxed::Box;
use engine::{EvalError, Engine};
use engine::{EvalError, Engine, Arity0, Arity1, Arity2, Arity3};
pub trait FnRegister {
fn register(self, engine: &mut Engine, name: &str);
@ -24,7 +24,7 @@ impl<T: Any+Clone, U: Any+Clone, V: Any+Clone, W: Any+Clone> FnRegister for fn(&
);
let ent = engine.fns_arity_3.entry(name.to_string()).or_insert(Vec::new());
(*ent).push(wrapped);
(*ent).push(Arity3::ExternalFn(wrapped));
}
}
@ -45,7 +45,7 @@ impl<T: Any+Clone, U: Any+Clone, V: Any+Clone, W: Any+Clone> FnRegister for fn(T
);
let ent = engine.fns_arity_3.entry(name.to_string()).or_insert(Vec::new());
(*ent).push(wrapped);
(*ent).push(Arity3::ExternalFn(wrapped));
}
}
@ -65,7 +65,7 @@ impl<T: Any+Clone, U: Any+Clone, V: Any+Clone> FnRegister for fn(&mut T, U)->V {
);
let ent = engine.fns_arity_2.entry(name.to_string()).or_insert(Vec::new());
(*ent).push(wrapped);
(*ent).push(Arity2::ExternalFn(wrapped));
}
}
@ -85,7 +85,7 @@ impl<T: Any+Clone, U: Any+Clone, V: Any+Clone> FnRegister for fn(T, U)->V {
);
let ent = engine.fns_arity_2.entry(name.to_string()).or_insert(Vec::new());
(*ent).push(wrapped);
(*ent).push(Arity2::ExternalFn(wrapped));
}
}
@ -104,7 +104,7 @@ impl<T: Any+Clone, U: Any+Clone> FnRegister for fn(&mut T)->U {
);
let ent = engine.fns_arity_1.entry(name.to_string()).or_insert(Vec::new());
(*ent).push(wrapped);
(*ent).push(Arity1::ExternalFn(wrapped));
}
}
@ -122,7 +122,7 @@ impl<T: Any+Clone, U: Any+Clone> FnRegister for fn(T)->U {
);
let ent = engine.fns_arity_1.entry(name.to_string()).or_insert(Vec::new());
(*ent).push(wrapped);
(*ent).push(Arity1::ExternalFn(wrapped));
}
}
@ -134,6 +134,6 @@ impl<T: Any+Clone> FnRegister for fn()->T {
);
let ent = engine.fns_arity_0.entry(name.to_string()).or_insert(Vec::new());
(*ent).push(wrapped);
(*ent).push(Arity0::ExternalFn(wrapped));
}
}

21
src/main.rs
View File

@ -23,17 +23,18 @@ fn showit<T: Display>(x: &mut T) -> () {
}
fn main() {
let mut engine = Engine::new();
&(showit as fn(x: &mut i32)->()).register(&mut engine, "print");
&(showit as fn(x: &mut i64)->()).register(&mut engine, "print");
&(showit as fn(x: &mut u32)->()).register(&mut engine, "print");
&(showit as fn(x: &mut u64)->()).register(&mut engine, "print");
&(showit as fn(x: &mut f32)->()).register(&mut engine, "print");
&(showit as fn(x: &mut f64)->()).register(&mut engine, "print");
&(showit as fn(x: &mut bool)->()).register(&mut engine, "print");
&(showit as fn(x: &mut String)->()).register(&mut engine, "print");
for fname in env::args().skip(1) {
let mut engine = Engine::new();
&(showit as fn(x: &mut i32)->()).register(&mut engine, "print");
&(showit as fn(x: &mut i64)->()).register(&mut engine, "print");
&(showit as fn(x: &mut u32)->()).register(&mut engine, "print");
&(showit as fn(x: &mut u64)->()).register(&mut engine, "print");
&(showit as fn(x: &mut f32)->()).register(&mut engine, "print");
&(showit as fn(x: &mut f64)->()).register(&mut engine, "print");
&(showit as fn(x: &mut bool)->()).register(&mut engine, "print");
&(showit as fn(x: &mut String)->()).register(&mut engine, "print");
if let Ok(mut f) = File::open(fname.clone()) {
let mut contents = String::new();
if let Ok(_) = f.read_to_string(&mut contents) {