frontend: simplify uses of comparison operators by mikesamuel · Pull Request #466 · temperlang/temper

mikesamuel · 2026-07-21T23:19:39Z

This is preparatory work to changing the IR of comparison operators. Just making sure that non-overridden operators, especially the Int32 variants, are directly available.

Also, instead of using the == and != cover functions in other desugarings, use simpler tests like isNull.

This required changing frontend and backend test goldens so I thought I'd get it out of the way first.

Specific changes:

Coalescing operator, ??, now uses isNull in its desugaring, not != null.
Comparison operators like < are no longer null accepting. be-rust no longer wraps f64 as options to compare them but == and != still are.
CoverFunction.uncover is now a static method so users like new and DotHelper no longer have to create CoverFunctions under the hood.
Hardcoded ASTs in tests like ControlFlowTest use specific comparison operators, not the cover function values.

This is preparatory work to changing the IR of comparison operators. Just making sure that non-overridden operators, especially the Int32 variants, are directly available. Also, instead of using the `==` and `!=` cover functions in other desugarings, use simpler tests like `isNull`. This required changing frontend and backend test goldens so I thought I'd get it out of the way first. Specific changes: - Coalescing operator, `??`, now uses `isNull` in its desugaring, not `!= null`. - Comparison operators like `<` are no longer null accepting. be-rust no longer wraps f64 as options to compare them but `==` and `!=` still are. - CoverFunction.uncover is now a static method so users like `new` and DotHelper no longer have to create CoverFunctions under the hood. - Hardcoded ASTs in tests like ControlFlowTest use specific comparison operators, not the cover function values. This is a draft. There is a failure in be-rust. Functional tests that depend on std, like typesDate fail. The use of `.cmp` below is flagged as an error. ```rs fn decodeHexUnsigned__361(sourceText__708: impl temper_core::ToArcString, start__709: usize, limit__710: usize) -> i32 { let sourceText__708 = sourceText__708.to_arc_string(); let return__307: i32; let mut t___1642: bool; let mut t___1644: bool; let mut t___1647: bool; let mut t___1650: i32; 'fn__711: { let mut n__712: i32 = 0; let mut i__713: usize = start__709; 'loop___2712: loop { if ! (Some(i__713).cmp( & Some(limit__710)) as i32 < 0) { break; } ``` It corresponds to code from std/json: ```ts let decodeHexUnsigned( sourceText: String, start: StringIndex, limit: StringIndex ): Int { var n = 0; var i = start; while (i.compareTo(limit) < 0) { ``` Signed-off-by: Mike Samuel <mikesamuel@gmail.com>

mikesamuel · 2026-07-21T23:22:46Z

https://hackmd.io/@temper/SknfNmaVGl

mikesamuel · 2026-07-21T23:23:40Z

        translator: RustTranslator,
    ): Rust.Expr {
+        val cmpFn = when (operator) {
+            RustOperator.Equals, RustOperator.NotEquals -> "cmp_option"


I want == and != for ints to eventually be non-null accepting, but for now, they still are.

mikesamuel · 2026-07-21T23:25:40Z

+        BuiltinOperatorId.LtIntInt,
+    ) { cmp ->
+        TBoolean.value(cmp < 0)
+    }


Exposing these out so that the non-overloaded version is readily available.

This will make it easier to desugar overloaded comparisons to a use of <=> nested inside a guaranteed int comparison of its output.

mikesamuel · 2026-07-21T23:26:07Z

                {
                    Call {
-                        V(Value(BuiltinFuns.notEqualsFn))
+                        V(vIsNullFn)


One fewer use of a cover function.

mikesamuel · 2026-07-21T23:26:38Z

    ("..." to OutputTokenType.Name) to false, // ...Int
    (OutputTokenType.Word to "(") to true, // if (
    (OutputTokenType.Name to "{") to true, // f {
+    (OutputTokenType.NumericValue to "{") to true, // if x == 0 {


Rust was formatting oddly: if x < 0{. Now there's a space before the bracket.

mikesamuel · 2026-07-21T23:27:20Z

      while (i.compareTo(limit) < 0) {
        let cp = sourceText[i];
-        let digit = if (char'0' <= cp && cp <= char'0') {
+        let digit = if (char'0' <= cp && cp <= char'9') {


mikesamuel · 2026-07-21T23:27:48Z

            accessibleMembers.isEmpty() && extensions.isNotEmpty() &&
            extensions.all { (it as? FunctionResolution)?.fn is CallableValue }
        ) {
-            val cover = CoverFunction(extensions.map { (it as FunctionResolution).fn as CallableValue })


Fewer creations of cover functions under the hood.

mikesamuel · 2026-07-21T23:28:35Z

-            TODO("Link to a macro environment so we can evaluate the value tree")
+            val (_, newValue) = newValues[index]
+                ?: TODO("Link to a macro environment so we can evaluate the value tree $index, $interpMode")
+            newValue.valueContained ?: Fail


new now cherry picks arguments to pass and the this argument reaches this path.

mikesamuel · 2026-07-21T23:29:23Z

+            cb: InterpreterCallback,
+            interpMode: InterpMode,
+            covered: List<CallableValue>,
+            otherwise: CallableValue? = null,


Only change from above is these two arguments passed in instead of being accessed as fields, and a change to the recursive call at L129.

Signed-off-by: Tom <tom@temper.systems>

tjpalmer · 2026-07-22T00:03:00Z

            |        let mut i__0: usize = start__0;
            |        'loop___0: loop {
-            |            if ! (Some(Some(i__0).cmp( & Some(limit__0)) as i32) < Some(0)) {
+            |            if ! (Some(i__0).cmp( & Some(limit__0)) as i32 < 0) {


Looks like the outer Some(...) was masking the now exposed as i32 < 0.

Address this error: ```rs --> C:\Users\work2\AppData\Local\Temp\temper-test3896171247360590248\rust\std\src\json\mod.rs:1782:64 | 1782 | if ! (Some(i__713).cmp( & Some(limit__710)) as i32 < 0) { | ^ -- interpreted as generic arguments | | | not interpreted as comparison | help: try comparing the cast value | 1782 | if ! ((Some(i__713).cmp( & Some(limit__710)) as i32) < 0) { | + + ```

Signed-off-by: Mike Samuel <mikesamuel@gmail.com>

tjpalmer · 2026-07-22T20:05:49Z

            |pub fn hi(n__0: i32) {
            |    let mut i__0: i32 = 0;
-            |    'loop___0: while Some(i__0) < Some(n__0) {
+            |    'loop___0: while i__0 < n__0 {


Losing the Some is nice.

Yeah. Comparisons were just doing too much. Uses of non-nullable types shouldn't pay for null-safety.

mikesamuel commented Jul 21, 2026

View reviewed changes

tjpalmer added 2 commits July 21, 2026 16:56

be-rust: Require parens for as inside cmp

1da4744

Signed-off-by: Tom <tom@temper.systems>

Fix backend tests

3f3210f

Signed-off-by: Tom <tom@temper.systems>

tjpalmer reviewed Jul 22, 2026

View reviewed changes

mikesamuel added 2 commits July 21, 2026 18:41

fix obvious bug in Temper code in a testcase

9243cd0

Signed-off-by: Mike Samuel <mikesamuel@gmail.com>

mikesamuel marked this pull request as ready for review July 22, 2026 16:48

tjpalmer approved these changes Jul 22, 2026

View reviewed changes

mikesamuel merged commit 2912533 into main Jul 22, 2026
2 checks passed

mikesamuel deleted the pre-cmp-refactoring branch July 22, 2026 21:10

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mikesamuel commented Jul 21, 2026 •

edited by tjpalmer

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