mist-script/src/parser/mod.rs

use pest::Parser;
use pest_derive::Parser;

pub mod ast;
use ast::*;

#[derive(Parser)]
#[grammar = "./src/parser/grammar.pest"]
pub struct MistParser;

// convenience alias for pest errors
pub type ParseError = pest::error::Error<Rule>;

pub fn parse(source: &str) -> Result<Vec<TopLevel>, ParseError> {
    let mut pairs = MistParser::parse(Rule::program, source)?;

    let mut statements = vec![];

    for pair in pairs.next().unwrap().into_inner() {
        if let Some(stmt) = TopLevel::from_pair(pair) {
            statements.push(stmt);
        }
    }

    Ok(statements)
}

impl TypeExpr {
    pub fn from_pair(pair: pest::iterators::Pair<Rule>) -> Self {
        match pair.as_rule() {
            Rule::type_expr => {
                let inner = pair.into_inner().next().unwrap();
                TypeExpr::from_pair(inner)
            }
            Rule::identifier => TypeExpr::Identifier(pair.as_str().to_string()),
            _ => unimplemented!("TypeExpr parsing not implemented yet"),
        }
    }
}

impl ParamList {
    pub fn from_pair(pair: pest::iterators::Pair<Rule>) -> Self {
        let params = pair
            .into_inner()
            .map(|p| {
                let mut param_inner = p.into_inner();
                let param_name = param_inner.next().unwrap().as_str().to_string();
                let param_type = TypeExpr::from_pair(param_inner.next().unwrap());
                (param_name, param_type)
            })
            .collect();

        ParamList(params)
    }
}

impl TopLevel {
    pub fn from_pair(pair: pest::iterators::Pair<Rule>) -> Option<Self> {
        match pair.as_rule() {
            Rule::import => {
                let path = pair.into_inner().next().unwrap().as_str().to_string();
                Some(TopLevel::Import(path))
            }
            Rule::function_decl => {
                let mut inner = pair.into_inner();

                let export = if let Some(first) = inner.peek() {
                    if first.as_rule() == Rule::export {
                        inner.next();
                        true
                    } else {
                        false
                    }
                } else {
                    false
                };
                let name = inner.next().unwrap().as_str().to_string();
                let params_pair = inner.next().unwrap();
                let params = if params_pair.as_rule() == Rule::param_list {
                    ParamList::from_pair(params_pair)
                } else {
                    ParamList(vec![])
                };
                let return_type = if let Some(next) = inner.peek() {
                    if next.as_rule() == Rule::type_expr {
                        Some(TypeExpr::from_pair(inner.next().unwrap()))
                    } else {
                        None
                    }
                } else {
                    None
                };

                let body = Block::from_pair(inner.next().unwrap());

                Some(TopLevel::FunctionDecl {
                    export,
                    name,
                    params,
                    return_type,
                    body,
                })
            }

            Rule::struct_decl => {
                let mut inner = pair.into_inner();
                let export = if let Some(first) = inner.peek() {
                    if first.as_rule() == Rule::export {
                        inner.next();
                        true
                    } else {
                        false
                    }
                } else {
                    false
                };
                let name = inner.next().unwrap().as_str().to_string();
                let fields_pair = inner.next().unwrap();
                let fields = ParamList::from_pair(fields_pair);

                Some(TopLevel::StructDecl {
                    export,
                    name,
                    fields,
                })
            }

            Rule::EOI => None,
            _ => unimplemented!("TopLevel parsing not implemented yet {:?}", pair.as_rule()),
        }
    }
}

impl Block {
    pub fn from_pair(pair: pest::iterators::Pair<Rule>) -> Self {
        let statements = pair
            .into_inner()
            .flat_map(|pair| {
                if pair.as_rule() == Rule::statement_list {
                    pair.into_inner().map(Statement::from_pair).collect()
                } else {
                    vec![Statement::from_pair(pair)]
                }
            })
            .collect();
        Block(statements)
    }
}

impl Statement {
    pub fn from_pair(pair: pest::iterators::Pair<Rule>) -> Self {
        match pair.as_rule() {
            Rule::statement => {
                let inner = pair.into_inner().next().unwrap();
                Statement::from_pair(inner)
            }
            Rule::expr_stmt => {
                let expr_pair = pair.into_inner().next().unwrap();
                Statement::Expression(Expression::from_pair(expr_pair))
            }
            _ => unimplemented!(
                "Statement parsing not implemented yet: {:?}",
                pair.as_rule()
            ),
        }
    }
}

impl Expression {
    pub fn from_pair(pair: pest::iterators::Pair<Rule>) -> Self {
        match pair.as_rule() {
            Rule::expr => {
                let inner = pair.into_inner().next().unwrap();
                Expression::from_pair(inner)
            }
            Rule::identifier => Expression::Identifier(pair.as_str().to_string()),
            Rule::integer => {
                let value = pair.as_str().parse::<i64>().unwrap();
                Expression::IntLiteral(value)
            }
            Rule::float => {
                let value = pair.as_str().parse::<f64>().unwrap();
                Expression::FloatLiteral(value)
            }
            Rule::boolean => {
                let value = pair.as_str().parse::<bool>().unwrap();
                Expression::BoolLiteral(value)
            }
            Rule::string_lit => {
                let inner_str = pair.into_inner().next().unwrap().as_str();
                Expression::StringLiteral(inner_str.to_string())
            }
            _ => unimplemented!("Expression parsing not implemented yet"),
        }
    }
}