Added basic parsing

- Expressions
- If, Functio

src/ast.rs

@@ -5,7 +5,7 @@
 //!
 //! Expressions are just operations and they cannot be
 //! used as statements. Functions in AbleScript are in fact
-//! just plain subroutines and they do not return any value, 
+//! just plain subroutines and they do not return any value,
 //! so their calls are statements.
 
 use crate::variables::Value;
@@ -18,6 +18,12 @@ pub struct Iden {
     pub span: Span,
 }
 
+impl Iden {
+    pub fn new(iden: String, span: Span) -> Self {
+        Self { iden, span }
+    }
+}
+
 #[derive(Debug)]
 pub struct Block {
     pub block: Vec<Stmt>,

src/error.rs

@@ -1,6 +1,6 @@
 use std::ops::Range;
 
-use crate::brian::InterpretError;
+use crate::{brian::InterpretError, lexer::Token};
 
 #[derive(Debug, Clone)]
 pub struct Error {
@@ -11,7 +11,8 @@ pub struct Error {
 #[derive(Debug, Clone)]
 pub enum ErrorKind {
     SyntaxError(String),
-    EndOfTokenStream,
+    UnexpectedEof,
+    UnexpectedToken(Token),
     InvalidIdentifier,
     UnknownVariable(String),
     MeloVariable(String),
@@ -19,4 +20,15 @@ pub enum ErrorKind {
     TopLevelBreak,
     ArithmeticError,
     BfInterpretError(InterpretError),
+    MissingLhs,
+}
+
+impl Error {
+    pub fn new(kind: ErrorKind, span: Range<usize>) -> Self {
+        Self { kind, span }
+    }
+
+    pub fn unexpected_eof() -> Self {
+        Self::new(ErrorKind::UnexpectedEof, 0..0)
+    }
 }

src/lexer.rs

@@ -6,10 +6,10 @@ use crate::variables::Abool;
 pub enum Token {
     // Symbols
     #[token("(")]
-    LeftParenthesis,
+    LeftParen,
 
     #[token(")")]
-    RightParenthesis,
+    RightParen,
 
     #[token("[")]
     LeftBracket,
@@ -184,8 +184,8 @@ mod tests {
         let expected = &[
             Functio,
             Identifier("test".to_owned()),
-            LeftParenthesis,
+            LeftParen,
-            RightParenthesis,
+            RightParen,
             LeftCurly,
             Variable,
             Identifier("a".to_owned()),

src/parser.rs

@@ -0,0 +1,261 @@
+//! AbleScript Parser
+//!
+//! Type of this parser is recursive descent
+
+use logos::{Lexer, Logos};
+
+use crate::ast::*;
+use crate::error::{Error, ErrorKind};
+use crate::lexer::Token;
+use crate::variables::Value;
+
+/// Parser structure which holds lexer and metadata
+///
+/// Make one using [`Parser::new`] function
+pub struct Parser<'source> {
+    lexer: Lexer<'source, Token>,
+}
+
+impl<'source> Parser<'source> {
+    /// Create a new parser from source code
+    pub fn new(source: &'source str) -> Self {
+        Self {
+            lexer: Token::lexer(source),
+        }
+    }
+
+    /// Start parsing tokens
+    ///
+    /// Loops trough lexer, parses statements, returns AST
+    pub fn init(&mut self) -> Result<Vec<Stmt>, Error> {
+        let mut ast = vec![];
+        while let Some(token) = self.lexer.next() {
+            ast.push(self.parse(token)?);
+        }
+        Ok(ast)
+    }
+
+    /// Parse a token
+    ///
+    /// This function will route to corresponding flow functions
+    /// which may advance the lexer iterator
+    fn parse(&mut self, token: Token) -> Result<Stmt, Error> {
+        let start = self.lexer.span().start;
+
+        match token {
+            Token::If => Ok(Stmt::new(self.if_flow()?, start..self.lexer.span().end)),
+            Token::Functio => Ok(Stmt::new(
+                self.functio_flow()?,
+                start..self.lexer.span().end,
+            )),
+            t => Err(Error {
+                kind: ErrorKind::UnexpectedToken(t),
+                span: start..self.lexer.span().end,
+            }),
+        }
+    }
+
+    /// Require next item to be equal with expected one
+    fn require(&mut self, expected: Token) -> Result<(), Error> {
+        match self.lexer.next() {
+            Some(t) if t == expected => Ok(()),
+            Some(t) => Err(Error::new(ErrorKind::UnexpectedToken(t), self.lexer.span())),
+            None => Err(Error::unexpected_eof()),
+        }
+    }
+
+    /// Get an Identifier
+    fn get_iden(&mut self) -> Result<Iden, Error> {
+        match self.lexer.next().ok_or(Error::unexpected_eof())? {
+            Token::Identifier(iden) => Ok(Iden {
+                iden,
+                span: self.lexer.span(),
+            }),
+            t => Err(Error::new(ErrorKind::UnexpectedToken(t), self.lexer.span())),
+        }
+    }
+
+    /// Parse an expression
+    ///
+    /// AbleScript strongly separates expressions from statements.
+    /// Expressions do not have any side effects and the are
+    /// only mathematial and logical operations or values.
+    fn parse_expr(&mut self, token: Token, buf: &mut Option<Expr>) -> Result<Expr, Error> {
+        let start = self.lexer.span().start;
+
+        match token {
+            // Values
+            Token::Identifier(i) => Ok(Expr::new(
+                ExprKind::Variable(i),
+                start..self.lexer.span().end,
+            )),
+            Token::Abool(a) => Ok(Expr::new(
+                ExprKind::Literal(Value::Abool(a)),
+                start..self.lexer.span().end,
+            )),
+            Token::Bool(b) => Ok(Expr::new(
+                ExprKind::Literal(Value::Bool(b)),
+                start..self.lexer.span().end,
+            )),
+            Token::Integer(i) => Ok(Expr::new(
+                ExprKind::Literal(Value::Int(i)),
+                start..self.lexer.span().end,
+            )),
+            Token::String(s) => Ok(Expr::new(
+                ExprKind::Literal(Value::Str(s)),
+                start..self.lexer.span().end,
+            )),
+            Token::Nul => Ok(Expr::new(
+                ExprKind::Literal(Value::Nul),
+                start..self.lexer.span().end,
+            )),
+
+            // Operations
+            Token::Plus => Ok(Expr::new(
+                self.op_flow(BinOpKind::Add, buf)?,
+                start..self.lexer.span().end,
+            )),
+            Token::Minus => Ok(Expr::new(
+                self.op_flow(BinOpKind::Subtract, buf)?,
+                start..self.lexer.span().end,
+            )),
+            Token::Star => Ok(Expr::new(
+                self.op_flow(BinOpKind::Multiply, buf)?,
+                start..self.lexer.span().end,
+            )),
+            Token::FwdSlash => Ok(Expr::new(
+                self.op_flow(BinOpKind::Divide, buf)?,
+                start..self.lexer.span().end,
+            )),
+            Token::EqualEqual => Ok(Expr::new(
+                self.op_flow(BinOpKind::Equal, buf)?,
+                start..self.lexer.span().end,
+            )),
+            Token::NotEqual => Ok(Expr::new(
+                self.op_flow(BinOpKind::NotEqual, buf)?,
+                start..self.lexer.span().end,
+            )),
+            Token::And => Ok(Expr::new(
+                self.op_flow(BinOpKind::And, buf)?,
+                start..self.lexer.span().end,
+            )),
+            Token::Or => Ok(Expr::new(
+                self.op_flow(BinOpKind::Or, buf)?,
+                start..self.lexer.span().end,
+            )),
+            Token::LessThan => Ok(Expr::new(
+                self.op_flow(BinOpKind::Less, buf)?,
+                start..self.lexer.span().end,
+            )),
+            Token::GreaterThan => Ok(Expr::new(
+                self.op_flow(BinOpKind::Greater, buf)?,
+                start..self.lexer.span().end,
+            )),
+
+            Token::Not => Ok(Expr::new(
+                {
+                    let next = self.lexer.next().ok_or(Error::unexpected_eof())?;
+                    ExprKind::Not(Box::new(self.parse_expr(next, buf)?))
+                },
+                start..self.lexer.span().end,
+            )),
+            Token::LeftParen => self.expr_flow(Token::RightParen),
+            t => Err(Error::new(
+                ErrorKind::UnexpectedToken(t),
+                start..self.lexer.span().end,
+            )),
+        }
+    }
+
+    /// Flow for operators
+    ///
+    /// Generates operation from LHS buffer and next expression as RHS
+    ///
+    /// This is unaware of precedence, as AbleScript do not have it
+    fn op_flow(&mut self, kind: BinOpKind, lhs: &mut Option<Expr>) -> Result<ExprKind, Error> {
+        Ok(ExprKind::BinOp {
+            lhs: Box::new(
+                lhs.take()
+                    .ok_or(Error::new(ErrorKind::MissingLhs, self.lexer.span()))?,
+            ),
+            rhs: {
+                let next = self.lexer.next().ok_or(Error::unexpected_eof())?;
+                Box::new(self.parse_expr(next, &mut None)?)
+            },
+            kind,
+        })
+    }
+
+    /// Parse expressions until terminate token
+    fn expr_flow(&mut self, terminate: Token) -> Result<Expr, Error> {
+        let mut buf = None;
+        Ok(loop {
+            match self.lexer.next().ok_or(Error::unexpected_eof())? {
+                t if t == terminate => break buf.take().unwrap(),
+                t => buf = Some(self.parse_expr(t, &mut buf)?),
+            }
+        })
+    }
+
+    /// Parse a list of statements between curly braces
+    fn parse_block(&mut self) -> Result<Block, Error> {
+        self.require(Token::LeftCurly)?;
+        let mut block = vec![];
+
+        loop {
+            match self.lexer.next().ok_or(Error::unexpected_eof())? {
+                Token::RightCurly => break,
+                t => block.push(self.parse(t)?),
+            }
+        }
+        Ok(Block { block })
+    }
+
+    /// Parse If flow
+    ///
+    /// Consists of condition and block, there is no else
+    fn if_flow(&mut self) -> Result<StmtKind, Error> {
+        self.require(Token::LeftParen)?;
+
+        let cond = self.expr_flow(Token::RightParen)?;
+        
+        let body = self.parse_block()?;
+
+        Ok(StmtKind::If { cond, body })
+    }
+
+    /// Parse functio flow
+    ///
+    /// functio $iden (a, b, c) { ... }
+    fn functio_flow(&mut self) -> Result<StmtKind, Error> {
+        let iden = self.get_iden()?;
+
+        self.require(Token::LeftParen)?;
+
+        let mut args = vec![];
+        loop {
+            match self.lexer.next().ok_or(Error::unexpected_eof())? {
+                Token::RightParen => break,
+                Token::Identifier(i) => {
+                    args.push(Iden::new(i, self.lexer.span()));
+
+                    match self.lexer.next().ok_or(Error::unexpected_eof())? {
+                        Token::Comma => continue,
+                        Token::RightParen => break,
+                        t => {
+                            return Err(Error::new(
+                                ErrorKind::UnexpectedToken(t),
+                                self.lexer.span(),
+                            ))
+                        }
+                    }
+                }
+                t => return Err(Error::new(ErrorKind::UnexpectedToken(t), self.lexer.span())),
+            }
+        }
+
+        let body = self.parse_block()?;
+
+        Ok(StmtKind::Functio { iden, args, body })
+    }
+}