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backend/src/evaluator.rs

@@ -0,0 +1,168 @@
+use crate::cell::{Cell, CellRef};
+use crate::parser::*;
+use crate::tokenizer::Literal;
+use std::collections::HashMap;
+use std::fmt;
+
+#[derive(Debug, PartialEq, Clone)]
+pub enum Eval {
+    Literal(Literal),
+}
+
+impl fmt::Display for Eval {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            Eval::Literal(lit) => write!(f, "{lit:?}"),
+        }
+    }
+}
+
+pub struct Evaluator {
+    cells: HashMap<CellRef, Cell>,
+}
+
+impl Evaluator {
+    pub fn new() -> Evaluator {
+        return Evaluator {
+            cells: HashMap::new(),
+        };
+    }
+
+    pub fn set_cell(&mut self, cell_ref: CellRef, raw_val: String) -> Result<(), String> {
+        if self.cells.contains_key(&cell_ref) && self.cells[&cell_ref].raw() == raw_val {
+            return Ok(());
+        }
+
+        let eval: Eval;
+
+        if let Some(c) = raw_val.chars().nth(0)
+            && c == '='
+        {
+            eval = self.evaluate(raw_val[1..].to_owned())?;
+        } else {
+            match self.evaluate(raw_val.to_owned()) {
+                Ok(e) => {
+                    eval = e;
+                }
+                Err(_) => eval = Eval::Literal(Literal::String(raw_val.to_owned())),
+            }
+        }
+
+        self.cells.insert(cell_ref, Cell::new(eval, raw_val));
+        Ok(())
+    }
+
+    pub fn get_cell(&mut self, cell_ref: CellRef) -> Result<(String, Eval), String> {
+        if !self.cells.contains_key(&cell_ref) {
+            return Err(format!("Cell at {:?} not found.", cell_ref));
+        }
+
+        let cell = &self.cells[&cell_ref];
+
+        Ok((cell.raw(), cell.eval()))
+    }
+
+    pub fn evaluate(&mut self, str: String) -> Result<Eval, String> {
+        let (mut expr, mut deps) = parse(&str)?;
+
+        self.evaluate_expr(&mut expr)
+    }
+
+    fn evaluate_expr(&mut self, expr: &mut Expr) -> Result<Eval, String> {
+        let res = match expr {
+            Expr::Literal(lit) => Eval::Literal(lit.clone()),
+            Expr::CellRef(re) => self.get_cell(re.to_owned())?.1,
+            Expr::Infix { op, lhs, rhs } => {
+                let lval = self.evaluate_expr(lhs)?;
+                let rval = self.evaluate_expr(rhs)?;
+
+                match op {
+                    InfixOp::ADD => eval_add(&lval, &rval)?,
+                    InfixOp::SUB => eval_sub(&lval, &rval)?,
+                    InfixOp::MUL => eval_mul(&lval, &rval)?,
+                    InfixOp::DIV => eval_div(&lval, &rval)?,
+                    _ => return Err(format!("Evaluation error: Unsupported operator {:?}", op)),
+                }
+            }
+            it => return Err(format!("Evaluation error: Unsupported expression {:?}", it)),
+        };
+
+        Ok(res)
+    }
+}
+
+fn eval_add(lval: &Eval, rval: &Eval) -> Result<Eval, String> {
+    match (lval, rval) {
+        (Eval::Literal(a), Eval::Literal(b)) => {
+            if let Some(res) = eval_numeric_infix(a, b, |x, y| x + y, |x, y| x + y) {
+                return Ok(Eval::Literal(res));
+            }
+
+            // Try string concatenation
+            if let (Literal::String(x), Literal::String(y)) = (a, b) {
+                let mut res = x.to_owned();
+                res.push_str(y);
+                return Ok(Eval::Literal(Literal::String(res)));
+            }
+
+            Err("Evaluation error: expected string or numeric types for ADD function.".to_string())
+        }
+    }
+}
+
+fn eval_sub(lval: &Eval, rval: &Eval) -> Result<Eval, String> {
+    match (lval, rval) {
+        (Eval::Literal(a), Eval::Literal(b)) => {
+            if let Some(res) = eval_numeric_infix(a, b, |x, y| x - y, |x, y| x - y) {
+                return Ok(Eval::Literal(res));
+            }
+
+            Err("Evaluation error: expected string or numeric types for SUB function.".to_string())
+        }
+    }
+}
+fn eval_mul(lval: &Eval, rval: &Eval) -> Result<Eval, String> {
+    match (lval, rval) {
+        (Eval::Literal(a), Eval::Literal(b)) => {
+            if let Some(res) = eval_numeric_infix(a, b, |x, y| x * y, |x, y| x * y) {
+                return Ok(Eval::Literal(res));
+            }
+
+            Err("Evaluation error: expected string or numeric types for MUL function.".to_string())
+        }
+    }
+}
+fn eval_div(lval: &Eval, rval: &Eval) -> Result<Eval, String> {
+    match (lval, rval) {
+        (Eval::Literal(a), Eval::Literal(b)) => {
+            if let Some(res) = eval_numeric_infix(a, b, |x, y| x / y, |x, y| x / y) {
+                return Ok(Eval::Literal(res));
+            }
+
+            Err("Evaluation error: expected string or numeric types for DIV function.".to_string())
+        }
+    }
+}
+
+fn eval_numeric_infix<FInt, FDouble>(
+    lhs: &Literal,
+    rhs: &Literal,
+    int_op: FInt,
+    double_op: FDouble,
+) -> Option<Literal>
+where
+    FInt: Fn(i64, i64) -> i64,
+    FDouble: Fn(f64, f64) -> f64,
+{
+    match (lhs, rhs) {
+        (Literal::Integer(a), Literal::Integer(b)) => Some(Literal::Integer(int_op(*a, *b))),
+        (Literal::Double(a), Literal::Double(b)) => Some(Literal::Double(double_op(*a, *b))),
+        (Literal::Integer(a), Literal::Double(b)) => {
+            Some(Literal::Double(double_op(*a as f64, *b)))
+        }
+        (Literal::Double(a), Literal::Integer(b)) => {
+            Some(Literal::Double(double_op(*a, *b as f64)))
+        }
+        _ => None,
+    }
+}