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//! Module implementing custom syntax for [`Engine`].
use crate::ast::Expr;
use crate::engine::EvalContext;
use crate::fn_native::SendSync;
use crate::stdlib::{boxed::Box, format, string::ToString};
use crate::token::{is_valid_identifier, Token};
use crate::{
Dynamic, Engine, EvalAltResult, ImmutableString, LexError, ParseError, Position, Shared,
StaticVec,
};
pub const MARKER_EXPR: &str = "$expr$";
pub const MARKER_BLOCK: &str = "$block$";
pub const MARKER_IDENT: &str = "$ident$";
/// A general expression evaluation trait object.
#[cfg(not(feature = "sync"))]
pub type FnCustomSyntaxEval =
dyn Fn(&mut EvalContext, &[Expression]) -> Result<Dynamic, Box<EvalAltResult>>;
/// A general expression evaluation trait object.
#[cfg(feature = "sync")]
pub type FnCustomSyntaxEval =
dyn Fn(&mut EvalContext, &[Expression]) -> Result<Dynamic, Box<EvalAltResult>> + Send + Sync;
/// A general expression parsing trait object.
#[cfg(not(feature = "sync"))]
pub type FnCustomSyntaxParse =
dyn Fn(&[ImmutableString], &str) -> Result<Option<ImmutableString>, ParseError>;
/// A general expression parsing trait object.
#[cfg(feature = "sync")]
pub type FnCustomSyntaxParse =
dyn Fn(&[ImmutableString], &str) -> Result<Option<ImmutableString>, ParseError> + Send + Sync;
/// An expression sub-tree in an [`AST`][crate::AST].
#[derive(Debug, Clone)]
pub struct Expression<'a>(&'a Expr);
impl<'a> From<&'a Expr> for Expression<'a> {
#[inline(always)]
fn from(expr: &'a Expr) -> Self {
Self(expr)
}
}
impl Expression<'_> {
/// If this expression is a variable name, return it. Otherwise [`None`].
#[inline(always)]
pub fn get_variable_name(&self) -> Option<&str> {
self.0.get_variable_access(true)
}
/// Get the expression.
#[inline(always)]
pub(crate) fn expr(&self) -> &Expr {
&self.0
}
/// Get the position of this expression.
#[inline(always)]
pub fn position(&self) -> Position {
self.0.position()
}
}
impl EvalContext<'_, '_, '_, '_, '_, '_, '_, '_, '_> {
/// Evaluate an [expression tree][Expression].
///
/// # WARNING - Low Level API
///
/// This function is very low level. It evaluates an expression from an [`AST`][crate::AST].
#[inline(always)]
pub fn eval_expression_tree(
&mut self,
expr: &Expression,
) -> Result<Dynamic, Box<EvalAltResult>> {
self.engine.eval_expr(
self.scope,
self.mods,
self.state,
self.lib,
self.this_ptr,
expr.expr(),
self.level,
)
}
}
/// Definition of a custom syntax definition.
pub struct CustomSyntax {
/// A parsing function to return the next keyword in a custom syntax based on the
/// keywords parsed so far.
pub parse: Box<FnCustomSyntaxParse>,
/// Custom syntax implementation function.
pub func: Shared<FnCustomSyntaxEval>,
/// Delta number of variables in the scope.
pub scope_delta: isize,
}
impl Engine {
/// Register a custom syntax with the [`Engine`].
///
/// * `keywords` holds a slice of strings that define the custom syntax.
/// * `new_vars` is the number of new variables declared by this custom syntax, or the number of variables removed (if negative).
/// * `func` is the implementation function.
///
/// # Notes
///
/// If `new_vars` is positive, then a number of new variables are expected to be pushed into the
/// current [`Scope`][crate::Scope].
///
/// If `new_vars` is negative, then it is expected that only the top `new_vars` variables in the
/// current [`Scope`][crate::Scope] will be _popped_. Do not randomly remove variables.
pub fn register_custom_syntax<S: AsRef<str> + Into<ImmutableString>>(
&mut self,
keywords: impl AsRef<[S]>,
new_vars: isize,
func: impl Fn(&mut EvalContext, &[Expression]) -> Result<Dynamic, Box<EvalAltResult>>
+ SendSync
+ 'static,
) -> Result<&mut Self, ParseError> {
let keywords = keywords.as_ref();
let mut segments: StaticVec<ImmutableString> = Default::default();
for s in keywords {
let s = s.as_ref().trim();
// skip empty keywords
if s.is_empty() {
continue;
}
let token = Token::lookup_from_syntax(s);
let seg = match s {
// Markers not in first position
MARKER_IDENT | MARKER_EXPR | MARKER_BLOCK if !segments.is_empty() => s.into(),
// Standard or reserved keyword/symbol not in first position
s if !segments.is_empty() && token.is_some() => {
// Make it a custom keyword/symbol if it is disabled or reserved
if (self.disabled_symbols.contains(s)
|| matches!(token, Some(Token::Reserved(_))))
&& !self.custom_keywords.contains_key(s)
{
self.custom_keywords.insert(s.into(), None);
}
s.into()
}
// Standard keyword in first position
s if segments.is_empty()
&& token
.as_ref()
.map(|v| v.is_keyword() || v.is_reserved())
.unwrap_or(false) =>
{
return Err(LexError::ImproperSymbol(
s.to_string(),
format!(
"Improper symbol for custom syntax at position #{}: '{}'",
segments.len() + 1,
s
),
)
.into_err(Position::NONE)
.into());
}
// Identifier in first position
s if segments.is_empty() && is_valid_identifier(s.chars()) => {
// Make it a custom keyword/symbol if it is disabled or reserved
if (self.disabled_symbols.contains(s)
|| matches!(token, Some(Token::Reserved(_))))
&& !self.custom_keywords.contains_key(s)
{
self.custom_keywords.insert(s.into(), None);
}
s.into()
}
// Anything else is an error
_ => {
return Err(LexError::ImproperSymbol(
s.to_string(),
format!(
"Improper symbol for custom syntax at position #{}: '{}'",
segments.len() + 1,
s
),
)
.into_err(Position::NONE)
.into());
}
};
segments.push(seg);
}
// If the syntax has no keywords, just ignore the registration
if segments.is_empty() {
return Ok(self);
}
// The first keyword is the discriminator
let key = segments[0].clone();
self.register_custom_syntax_raw(
key,
// Construct the parsing function
move |stream, _| {
if stream.len() >= segments.len() {
Ok(None)
} else {
Ok(Some(segments[stream.len()].clone()))
}
},
new_vars,
func,
);
Ok(self)
}
/// Register a custom syntax with the [`Engine`].
///
/// # WARNING - Low Level API
///
/// This function is very low level.
///
/// * `new_vars` is the number of new variables declared by this custom syntax, or the number of variables removed (if negative).
/// * `parse` is the parsing function.
/// * `func` is the implementation function.
///
/// All custom keywords must be manually registered via [`Engine::register_custom_operator`].
/// Otherwise, custom keywords won't be recognized.
pub fn register_custom_syntax_raw(
&mut self,
key: impl Into<ImmutableString>,
parse: impl Fn(&[ImmutableString], &str) -> Result<Option<ImmutableString>, ParseError>
+ SendSync
+ 'static,
new_vars: isize,
func: impl Fn(&mut EvalContext, &[Expression]) -> Result<Dynamic, Box<EvalAltResult>>
+ SendSync
+ 'static,
) -> &mut Self {
let syntax = CustomSyntax {
parse: Box::new(parse),
func: (Box::new(func) as Box<FnCustomSyntaxEval>).into(),
scope_delta: new_vars,
};
self.custom_syntax.insert(key.into(), syntax);
self
}
}