177 lines
5.1 KiB
Markdown
177 lines
5.1 KiB
Markdown
# Advanced Static Typing
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Claro v1.18.26 adds the first advanced static-typing foundation: typed containers checked by `claro typecheck`.
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## Typed lists
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```claro
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SET names AS LIST OF TEXT TO LIST
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ADD "Ada" TO names
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ADD "Grace" TO names
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```
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The type checker now rejects wrong item types:
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```claro
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SET names AS LIST OF TEXT TO LIST
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ADD 123 TO names
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```
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Output:
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```text
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Type mismatch for list names: expected TEXT item, but this value looks like NUMBER.
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```
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## Typed maps
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```claro
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SET scores AS MAP OF NUMBER TO MAP
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PUT scores KEY "math" VALUE 98
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```
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The type checker rejects wrong value types:
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```claro
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SET scores AS MAP OF NUMBER TO MAP
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PUT scores KEY "oops" VALUE "high"
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```
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Output:
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```text
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Type mismatch for map scores: expected NUMBER value, but this value looks like TEXT.
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```
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## Function parameter checks
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Claro now has a small static-checking foundation for function arguments. Keep the beginner-friendly function syntax, then put the expected type inside the function with `CHECK TYPE`:
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```claro
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TEACH square amount
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CHECK TYPE amount IS NUMBER
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SAY amount
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END
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DO square 4
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```
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If a learner calls the function with the wrong kind of value, `claro typecheck` explains which parameter needs which type:
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```claro
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TEACH square amount
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CHECK TYPE amount IS NUMBER
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SAY amount
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END
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DO square "oops"
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```
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Output:
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```text
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Type mismatch for function square: parameter amount needs NUMBER, but this argument looks like TEXT.
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```
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Multiple checked parameters are reported separately, so a learner can fix each argument one at a time:
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```claro
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TEACH label TAKES name, age
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CHECK TYPE name IS TEXT
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CHECK TYPE age IS NUMBER
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SAY name
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SAY age
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END
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CALL label WITH 7, "old"
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```
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Output:
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```text
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Type mismatch for function label: parameter name needs TEXT, but this argument looks like NUMBER.
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Type mismatch for function label: parameter age needs NUMBER, but this argument looks like TEXT.
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```
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## Object method parameter checks
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Claro also checks simple object method arguments when the method body names a parameter with `CHECK TYPE`. This keeps the method syntax beginner-readable while giving a clearer error before the program runs:
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```claro
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CLASS Player
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HAS score NUMBER
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TEACH add points
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CHECK TYPE points IS NUMBER
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SET score score + points
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END
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END
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NEW Player player
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DO player.add 5
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```
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If the learner passes text where the method expects a number:
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```claro
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DO player.add "five"
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```
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Output:
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```text
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Type mismatch for method Player.add: parameter points needs NUMBER, but this argument looks like TEXT.
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```
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Both sides of this narrow method foundation are covered by validation: `tests/typecheck_method_good.claro` checks that `DO player.add 5` is accepted, and `tests/typecheck_method_bad.claro` checks the friendly wrong-type diagnostic.
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## Object field assignment checks
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Claro also has a narrow static diagnostic for direct object-field assignments. If a class declares a typed field and a script creates a simple object with `NEW Class name`, `claro typecheck` remembers the field type:
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```claro
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CLASS Player
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HAS score NUMBER
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END
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NEW Player player
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SET player.score 10
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```
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If a learner assigns the wrong value type directly to that known field:
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```claro
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SET player.score "ten"
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```
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Output:
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```text
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Type mismatch for field player.score: expected NUMBER, but this value looks like TEXT.
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```
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If a learner assigns to a field the class did not declare, `claro typecheck` now names the object class and suggests the matching `HAS` line:
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```claro
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CLASS Player
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HAS score NUMBER
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END
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NEW Player player
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SET player.level 3
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```
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Output:
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```text
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Object Player has no field level. Check the field name or add HAS level NUMBER to the class.
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```
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Both sides of this narrow field foundation are covered by validation: `tests/typecheck_object_field_good.claro` checks that `SET player.score 10` is accepted for a `HAS score NUMBER` field, `tests/typecheck_object_field_text_good.claro` checks that `SET player.name "Ada"` is accepted for a `HAS name TEXT` field, `tests/typecheck_object_field_yesno_good.claro` checks that `SET player.ready YES` is accepted for a `HAS ready YESNO` field, `tests/typecheck_object_field_bad.claro` checks the NUMBER wrong-type diagnostic, `tests/typecheck_object_field_text_bad.claro` checks the TEXT wrong-type diagnostic, `tests/typecheck_object_field_yesno_bad.claro` checks the YESNO wrong-type diagnostic, and `tests/typecheck_object_field_unknown_bad.claro` checks the unknown-field diagnostic.
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This slice is intentionally small: it covers direct `NEW Class object` plus `SET object.field value` cases in one file. Broader object flows, aliases, method return checks, and richer object signatures remain future work.
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## Status
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This is currently a static checker feature. It improves `claro typecheck` and validation confidence for `DO` and compatibility `CALL ... WITH` function calls, simple `DO object.method ...` calls where the object was created with `NEW Class name`, and direct assignments to known object fields. Runtime enforcement for every container mutation and richer function/object signatures can be added later after the syntax is classroom-tested.
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