Join semantics

src/eval/mod.rs

@@ -327,7 +327,8 @@ impl Eval for BlockExpr {
 
         let mut output = Value::None;
         for expr in &self.exprs {
-            output = expr.eval(ctx);
+            let value = expr.eval(ctx);
+            output = output.join(ctx, value, expr.span());
         }
 
         if self.scoping {
@@ -584,19 +585,15 @@ impl Eval for WhileExpr {
     type Output = Value;
 
     fn eval(&self, ctx: &mut EvalContext) -> Self::Output {
-        let mut output = vec![];
+        let mut output = Value::None;
         loop {
             let condition = self.condition.eval(ctx);
             if let Some(condition) = ctx.cast(condition, self.condition.span()) {
                 if condition {
-                    match self.body.eval(ctx) {
-                        Value::Template(v) => output.extend(v),
-                        Value::Str(v) => output.push(TemplateNode::Str(v)),
-                        Value::Error => return Value::Error,
-                        _ => {}
-                    }
+                    let value = self.body.eval(ctx);
+                    output = output.join(ctx, value, self.body.span());
                 } else {
-                    return Value::Template(output);
+                    return output;
                 }
             } else {
                 return Value::Error;
@@ -611,26 +608,19 @@ impl Eval for ForExpr {
     fn eval(&self, ctx: &mut EvalContext) -> Self::Output {
         macro_rules! iter {
             (for ($($binding:ident => $value:ident),*) in $iter:expr) => {{
-                let mut output = vec![];
+                let mut output = Value::None;
                 ctx.scopes.enter();
 
                 #[allow(unused_parens)]
                 for ($($value),*) in $iter {
                     $(ctx.scopes.def_mut($binding.as_str(), $value);)*
 
-                    match self.body.eval(ctx) {
-                        Value::Template(v) => output.extend(v),
-                        Value::Str(v) => output.push(TemplateNode::Str(v)),
-                        Value::Error => {
-                            ctx.scopes.exit();
-                            return Value::Error;
-                        }
-                        _ => {}
-                    }
+                    let value = self.body.eval(ctx);
+                    output = output.join(ctx, value, self.body.span());
                 }
 
                 ctx.scopes.exit();
-                Value::Template(output)
+                output
             }};
         }
 

src/eval/ops.rs

@@ -3,6 +3,33 @@ use std::cmp::Ordering::*;
 use super::{TemplateNode, Value};
 use Value::*;
 
+/// Join a value with another value.
+pub fn join(lhs: Value, rhs: Value) -> Result<Value, Value> {
+    Ok(match (lhs, rhs) {
+        (_, Error) => Error,
+        (Error, _) => Error,
+
+        (a, None) => a,
+        (None, b) => b,
+
+        (Str(a), Str(b)) => Str(a + &b),
+        (Array(a), Array(b)) => Array(concat(a, b)),
+        (Dict(a), Dict(b)) => Dict(concat(a, b)),
+
+        (Template(a), Template(b)) => Template(concat(a, b)),
+        (Template(mut a), Str(b)) => Template({
+            a.push(TemplateNode::Str(b));
+            a
+        }),
+        (Str(a), Template(mut b)) => Template({
+            b.insert(0, TemplateNode::Str(a));
+            b
+        }),
+
+        (a, _) => return Err(a),
+    })
+}
+
 /// Apply the plus operator to a value.
 pub fn pos(value: Value) -> Value {
     match value {
@@ -60,8 +87,6 @@ pub fn add(lhs: Value, rhs: Value) -> Value {
         (Dict(a), Dict(b)) => Dict(concat(a, b)),
 
         (Template(a), Template(b)) => Template(concat(a, b)),
-        (Template(a), None) => Template(a),
-        (None, Template(b)) => Template(b),
         (Template(mut a), Str(b)) => Template({
             a.push(TemplateNode::Str(b));
             a

src/eval/value.rs

@@ -5,6 +5,7 @@ use std::fmt::{self, Debug, Display, Formatter};
 use std::ops::Deref;
 use std::rc::Rc;
 
+use super::ops;
 use super::EvalContext;
 use crate::color::{Color, RgbaColor};
 use crate::exec::ExecContext;
@@ -61,14 +62,6 @@ impl Value {
         Self::Template(vec![TemplateNode::Func(TemplateFunc::new(name, f))])
     }
 
-    /// Try to cast the value into a specific type.
-    pub fn cast<T>(self) -> CastResult<T, Self>
-    where
-        T: Cast<Value>,
-    {
-        T::cast(self)
-    }
-
     /// The name of the stored value's type.
     pub fn type_name(&self) -> &'static str {
         match self {
@@ -125,6 +118,26 @@ impl Value {
             _ => None,
         }
     }
+
+    /// Try to cast the value into a specific type.
+    pub fn cast<T>(self) -> CastResult<T, Self>
+    where
+        T: Cast<Value>,
+    {
+        T::cast(self)
+    }
+
+    /// Join with another value.
+    pub fn join(self, ctx: &mut EvalContext, other: Self, span: Span) -> Self {
+        let (lhs, rhs) = (self.type_name(), other.type_name());
+        match ops::join(self, other) {
+            Ok(joined) => joined,
+            Err(prev) => {
+                ctx.diag(error!(span, "cannot join {} with {}", lhs, rhs));
+                prev
+            }
+        }
+    }
 }
 
 impl Default for Value {

tests/typ/code/block-invalid.typ

@@ -7,8 +7,9 @@
 {1u}
 
 // Should output `1`.
-// Error: 3 expected semicolon or line break
-{0 1}
+// Error: 2:3 expected semicolon or line break
+// Error: 1:4-1:5 cannot join integer with integer
+{1 2}
 
 // Should output `2`.
 // Error: 2:12 expected semicolon or line break

tests/typ/code/block.typ

@@ -9,7 +9,7 @@ All none
 // Let evaluates to none.
 { let v = 0 }
 
-// Trailing none evaluates to none.
+// Type is joined with trailing none, evaluates to string.
 {
     type("")
     none
@@ -19,15 +19,35 @@ All none
 // Evaluates to single expression.
 { "Hello" }
 
-// Evaluates to trailing expression.
+// Evaluates to string.
 { let x = "Hel"; x + "lo" }
 
-// Evaluates to concatenation of for loop bodies.
+// Evaluates to join of none, [He] and the two loop bodies.
 {
-    let parts = ("Hel", "lo")
+    let parts = ("l", "lo")
+    [He]
     for s in parts [{s}]
 }
 
+---
+// Evaluates to join of the templates and strings.
+{
+    [Hey, ]
+    if true {
+        "there!"
+    }
+    [ ]
+    if false [Nope]
+    [How are ] + "you?"
+}
+
+{
+    [A]
+    // Error: 5-6 cannot join template with integer
+    1
+    [B]
+}
+
 ---
 // Works the same way in code environment.
 // Ref: false

tests/typ/code/for.typ

@@ -20,14 +20,13 @@
 
 // String.
 {
-    let out = ""
     let first = true
-    for c in "abc" {
+    let out = for c in "abc" {
         if not first {
-            out += ", "
+            ", "
         }
+        c
         first = false
-        out += c
     }
     test(out, "a, b, c")
 }
@@ -36,14 +35,16 @@
 // Block body.
 // Should output `[1st, 2nd, 3rd, 4th, 5th, 6th]`.
 {
-    "[" + for v in (1, 2, 3, 4, 5, 6) {
-        (if v > 1 [, ]
-            + [{v}]
-            + if v == 1 [st]
-            + if v == 2 [nd]
-            + if v == 3 [rd]
-            + if v >= 4 [th])
-     } + "]"
+    "["
+    for v in (1, 2, 3, 4, 5, 6) {
+        if v > 1 [, ]
+        [#v]
+        if v == 1 [st]
+        if v == 2 [nd]
+        if v == 3 [rd]
+        if v >= 4 [th]
+     }
+     "]"
 }
 
 // Template body.
@@ -53,8 +54,8 @@
 ---
 // Value of for loops.
 // Ref: false
-#test(type(for v in () {}), "template")
-#test(type(for v in () []), "template")
+#test(for v in "" [], none)
+#test(type(for v in "1" []), "template")
 
 ---
 // Ref: false
@@ -67,7 +68,7 @@
 // Error: 11-18 cannot add integer and string
 #for v in 1 + "2" {}
 
-// A single error stops iteration.
+// Errors taint everything.
 #test(error, for v in (1, 2, 3) {
     if v < 2 [Ok] else {error}
 })

tests/typ/code/while.typ

@@ -23,8 +23,10 @@
 // Value of while loops.
 // Ref: false
 
-#test(type(while false {}), "template")
-#test(type(while false []), "template")
+#test(while false {}, none)
+
+#let i = 0
+#test(type(while i < 1 [{ i += 1 }]), "template")
 
 ---
 // Ref: false
@@ -37,13 +39,13 @@
 // Error: 8-15 unknown variable
 #while nothing {}
 
-// A single error stops iteration.
+// Errors taint everything.
 #let i = 0
 #test(error, while i < 10 {
     i += 1
     if i < 5 [nope] else { error }
 })
-#test(i, 5)
+#test(i, 10)
 
 ---
 // Error: 7 expected expression

tests/typeset.rs

@@ -327,10 +327,8 @@ fn register_helpers(scope: &mut Scope, panics: Rc<RefCell<Vec<Panic>>>) {
         let rhs = args.expect::<Value>(ctx, "right-hand side");
         if lhs != rhs {
             panics.borrow_mut().push(Panic { pos: args.span.start, lhs, rhs });
-            Value::Str(format!("(panic)"))
-        } else {
-            Value::None
         }
+        Value::None
     };
 
     scope.def_const("error", Value::Error);