Introduce Approx

src/eval.rs

@@ -23,6 +23,7 @@ pub enum Evaluated {
     // Literals
     Int(i64),
     Frac(Fraction),
+    Approx(f64),
     EmptyStr,
     Str(String),
     InterpolatedStr(Vec<(String, Ident)>, String),
@@ -61,6 +62,7 @@ pub fn scoped_eval(expr: Located<Expr>, vars: &Scope) -> Evaluated {
         Expr::EmptyStr => EmptyStr,
         Expr::Str(string) => Str(string),
         Expr::Frac(numerator, denominator) => Frac(fraction_from_i64s(numerator, denominator)),
+        Expr::Approx(num) => Approx(num),
         Expr::Char(ch) => Char(ch),
         Expr::Closure(args, body) => Closure(args.into_iter().map(|e| e.value).collect(), body, vars.clone()),
         Expr::EmptyRecord => EmptyRecord,
@@ -381,7 +383,6 @@ fn eval_operator(region: Region, left_expr: &Evaluated, op: Operator, right_expr
         (_, Caret, _) => EvalError(region, TypeMismatch("tried to use ^ on non-numbers".to_string())),
 
         // Slash
-        (Int(left_num), Slash, Int(right_num)) => Int(left_num.checked_div(*right_num).unwrap_or_else(|| panic!("Integer underflow on /"))),
         (Frac(left_num), Slash, Frac(right_num)) => {
             let answer = left_num / right_num;
 
@@ -392,22 +393,44 @@ fn eval_operator(region: Region, left_expr: &Evaluated, op: Operator, right_expr
             }
         },
 
+        (Int(_), Slash, Int(_)) => EvalError(region, TypeMismatch("tried to divide two Int values. Explicitly convert them to Frac values, or use Int division (the // operator).".to_string())),
+        (Approx(_), Slash, Approx(_)) => EvalError(region, TypeMismatch("tried to divide two Approx values. Explicitly convert them to Frac values, or use Approx division (the ~/ operator).".to_string())),
         (Int(_), Slash, Frac(_)) => EvalError(region, TypeMismatch("tried to divide Int by Frac. Explicitly convert them to the same type first!".to_string())),
-
         (Frac(_), Slash, Int(_)) => EvalError(region, TypeMismatch("tried to divide Frac by Int. Explicitly convert them to the same type first!".to_string())),
 
         (_, Slash, _) => EvalError(region, TypeMismatch("tried to divide non-numbers".to_string())),
 
         // DoubleSlash
         (Int(left_num), DoubleSlash, Int(right_num)) => Int(left_num / right_num),
-        (Frac(_), DoubleSlash, Frac(_)) => EvalError(region, TypeMismatch("tried to do integer division on two Frac values".to_string())),
 
+        (Approx(_), DoubleSlash, Approx(_)) => EvalError(region, TypeMismatch("tried to do integer division on two Approx values. Explicitly convert them to Int values, or use Approx division (the ~/ operator).".to_string())),
+        (Frac(_), DoubleSlash, Frac(_)) => EvalError(region, TypeMismatch("tried to do integer division on two Frac values. Explicitly conver them to Int values, or use Frac division (the / operator).".to_string())),
         (Int(_), DoubleSlash, Frac(_)) => EvalError(region,TypeMismatch("tried to integer-divide Int by Frac".to_string())),
-
         (Frac(_), DoubleSlash, Int(_)) => EvalError(region, TypeMismatch("tried to integer-divide Frac by Int".to_string())),
 
         (_, DoubleSlash, _) => EvalError(region, TypeMismatch("tried to do integer division on two non-numbers".to_string())),
 
+        // TildeSlash
+        (Approx(left_num), TildeSlash, Approx(right_num)) => {
+            let answer = left_num / right_num;
+
+            if answer.is_finite() {
+                ok_variant(Approx(answer))
+            } else {
+                err_variant(ApplyVariant("DivisionByZero".to_string(), None))
+            }
+        },
+
+        (Int(_), TildeSlash, Int(_)) => EvalError(region, TypeMismatch("tried to do Approx division on two Int values. Explicitly convert them to Approx values, or use Int division (the // operator).".to_string())),
+        (Frac(_), TildeSlash, Frac(_)) => EvalError(region, TypeMismatch("tried to do Approx division on two Frac values. Explicitly conver them to Approx values, or use Frac division (the / operator).".to_string())),
+        (Int(_), TildeSlash, Approx(_)) => EvalError(region, TypeMismatch("tried to do Int ~/ Approx. Explicitly convert both to Approx first!".to_string())),
+        (Frac(_), TildeSlash, Approx(_)) => EvalError(region, TypeMismatch("tried to do Frac ~/ Approx. Explicitly convert both to Approx first!".to_string())),
+
+        (Approx(_), TildeSlash, Int(_)) => EvalError(region, TypeMismatch("tried to divide Approx ~/ Int. Explicitly convert both to Approx first!".to_string())),
+        (Approx(_), TildeSlash, Frac(_)) => EvalError(region, TypeMismatch("tried to divide Approx ~/ Frac. Explicitly convert both to Approx first!".to_string())),
+
+        (_, TildeSlash, _) => EvalError(region, TypeMismatch("tried to divide non-numbers".to_string())),
+
         // Percent
         (Int(left_num), Percent, Int(right_num)) => Int(left_num % right_num),
         (Frac(left_num), Percent, Frac(right_num)) => {

src/expr.rs

@@ -9,6 +9,7 @@ pub enum Expr {
     // Literals
     Int(i64),
     Frac(i64, i64),
+    Approx(f64),
     EmptyStr,
     Str(String),
     InterpolatedStr(Vec<(String, Located<Ident>)>, String),
@@ -55,7 +56,7 @@ impl Expr {
         let transformed = transform(self);
 
         match transformed {
-            Int(_) | Frac(_, _) | EmptyStr | Str(_) | Char(_) | Var(_) | EmptyRecord | InterpolatedStr(_, _) => transformed,
+            Int(_) | Frac(_, _) | Approx(_) | EmptyStr | Str(_) | Char(_) | Var(_) | EmptyRecord | InterpolatedStr(_, _) => transformed,
             Assign(pattern, expr1, expr2) => {
                 Assign(
                     pattern,

src/operator.rs

@@ -5,7 +5,7 @@ use self::Operator::*;
 pub enum Operator {
     // highest precedence
     Caret,
-    Star, Slash, DoubleSlash, Percent,
+    Star, Slash, DoubleSlash, TildeSlash, Percent,
     Plus, Minus,
     Equals, LessThan, GreaterThan, LessThanOrEq, GreaterThanOrEq,
     And,
@@ -40,7 +40,7 @@ impl Operator {
         use self::Associativity::*;
 
         match self {
-            Pizza | Star | Slash | DoubleSlash | Percent | Plus | Minus => LeftAssociative,
+            Pizza | Star | Slash | DoubleSlash | TildeSlash | Percent | Plus | Minus => LeftAssociative,
             And | Or | Caret => RightAssociative,
             Equals | LessThan | GreaterThan | LessThanOrEq | GreaterThanOrEq => NonAssociative
         }
@@ -49,7 +49,7 @@ impl Operator {
 	fn precedence(&self) -> u8 {
         match self {
             Caret => 7,
-            Star | Slash | DoubleSlash | Percent => 6,
+            Star | Slash | DoubleSlash | TildeSlash | Percent => 6,
             Plus | Minus => 5,
             Equals | LessThan | GreaterThan | LessThanOrEq | GreaterThanOrEq => 4,
             And => 3,

src/parse.rs

@@ -207,7 +207,7 @@ parser! {
             apply_with_parens(min_indent),
             string("{}").with(value(Expr::EmptyRecord)),
             string_literal(),
-            number_literal(),
+            int_or_frac_literal(),
             char_literal(),
             if_expr(min_indent),
             case_expr(min_indent),
@@ -433,6 +433,18 @@ where I: Stream<Item = char, Position = IndentablePosition>,
             char('>').map(|_| Operator:: Pizza)
                 .or(char('|').map(|_| Operator::Or))
         ),
+        // either / or //
+        char('/').with(
+            optional(char('/'))
+                .map(|opt_slash| {
+                    if opt_slash.is_none() {
+                        Operator::Slash
+                    } else {
+                        Operator::DoubleSlash
+                    }
+                })
+        ),
+        string("~/").map(|_| Operator::TildeSlash),
         char('+').map(|_| Operator::Plus),
         char('-').map(|_| Operator::Minus),
         char('*').map(|_| Operator::Star),
@@ -526,7 +538,7 @@ parser! {
             char('_').map(|_| Pattern::Underscore),
             string("{}").map(|_| Pattern::EmptyRecordLiteral),
             match_variant(min_indent),
-            number_pattern(), // This goes before ident() so number literals aren't mistaken for malformed idents.
+            int_or_frac_pattern(), // This goes before ident() so number literals aren't mistaken for malformed idents.
             ident().map(|name| Pattern::Identifier(name)),
         ))
     }
@@ -787,7 +799,7 @@ where
     })
 }
 
-pub fn number_literal<I>() -> impl Parser<Input = I, Output = Expr>
+pub fn int_or_frac_literal<I>() -> impl Parser<Input = I, Output = Expr>
 where I: Stream<Item = char, Position = IndentablePosition>,
     I::Error: ParseError<I::Item, I::Range, I::Position>
 {
@@ -810,24 +822,24 @@ where I: Stream<Item = char, Position = IndentablePosition>,
         ))
     );
 
+    // Do this lookahead to decide if we should parse this as a number.
+    // This matters because once we commit to parsing it as a number,
+    // we may discover non-digit chars, indicating this is actually an
+    // invalid identifier. (e.g. "523foo" looks like a number, but turns
+    // out to be an invalid identifier on closer inspection.)
     optional(attempt(char('-')))
-        // Do this lookahead to decide if we should parse this as a number.
+        .skip(look_ahead(digit()))
-        // This matters because once we commit to parsing it as a number,
-        // we may discover non-digit chars, indicating this is actually an
-        // invalid identifier. (e.g. "523foo" looks like a number, but turns
-        // out to be an invalid identifier on closer inspection.)
-        .and(look_ahead(digit()))
         .and(digits_before_decimal)
         .and(optional(char('.').with(digits_after_decimal)))
-        .then(|(((opt_minus, _), int_digits), decimals): (((Option<char>, _), Vec<char>), Option<Vec<char>>)| {
+        .then(|((opt_minus, int_digits), decimals): ((Option<char>, Vec<char>), Option<Vec<char>>)| {
-            let is_positive = opt_minus.is_none();
+            let is_non_negative = opt_minus.is_none();
 
             // TODO check length of digits and make sure not to overflow
             let int_str: String = int_digits.into_iter().collect();
 
             match ( int_str.parse::<i64>(), decimals ) {
                 (Ok(int_val), None) => {
-                    if is_positive {
+                    if is_non_negative {
                         value(Expr::Int(int_val as i64)).right()
                     } else {
                         value(Expr::Int(-int_val as i64)).right()
@@ -844,7 +856,7 @@ where I: Stream<Item = char, Position = IndentablePosition>,
                             // Only the numerator may ever be signed!
                             let numerator = (int_val * denom) + (decimal as i64);
 
-                            if is_positive {
+                            if is_non_negative {
                                 value(Expr::Frac(numerator, denom)).right()
                             } else {
                                 value(Expr::Frac(-numerator, denom)).right()
@@ -861,11 +873,11 @@ where I: Stream<Item = char, Position = IndentablePosition>,
         })
 }
 
-/// TODO find a way to remove the code duplication between this and number_literal
+/// TODO find a way to remove the code duplication between this and int_or_frac_literal
 /// without sacrificing performance. I attempted to do this in 0062e83d03d389f0f07e33e1e7929e77825d774f
 /// but couldn't figure out how to address the resulting compiler error, which was:
 /// "cannot move out of captured outer variable in an `FnMut` closure"
-pub fn number_pattern<I>() -> impl Parser<Input = I, Output = Pattern>
+pub fn int_or_frac_pattern<I>() -> impl Parser<Input = I, Output = Pattern>
 where I: Stream<Item = char, Position = IndentablePosition>,
     I::Error: ParseError<I::Item, I::Range, I::Position>
 {

tests/test_parse.rs

@@ -30,7 +30,7 @@ mod test_parse {
     /// having to account for that.
     fn zero_loc_expr(expr: Expr) -> Expr {
         match expr {
-            Int(_) | Frac(_, _) | EmptyStr | Str(_) | Char(_) | Var(_) | EmptyRecord => expr,
+            Int(_) | Frac(_, _) | Approx(_) | EmptyStr | Str(_) | Char(_) | Var(_) | EmptyRecord => expr,
             InterpolatedStr(pairs, string) => InterpolatedStr(pairs.into_iter().map(|( prefix, ident )| ( prefix, zero_loc(ident))).collect(), string),
             Assign(pattern, expr1, expr2) => Assign(loc(pattern.value), loc_box(zero_loc_expr((*expr1).value)), loc_box(zero_loc_expr((*expr2).value))),
             CallByName(ident, args) => CallByName(ident, args.into_iter().map(|arg| loc(zero_loc_expr(arg.value))).collect()),