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Type-system diagnostics

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Type-system diagnostics use the E4000-E4999 range.

E4001 - Unknown type

• Category: Type System
• Explanation: A declaration names a type not provided by the implemented language.

• Trigger:

  Counter: word;
  

• Expected compiler output:

  E4001 demo.nsp:1:10
  
  Unknown type: word.
  

• Suggested fix: Use nes_color, byte, boolean, sprite, or metasprite.

E4002 - Invalid nes_color value

• Category: Type System
• Explanation: nes_color values are limited to the NES palette range $00..$3F in declarations, assignments, and every palette API.

• Trigger:

  BackgroundColor := $80;
  

• Expected compiler output:

  E4002 demo.nsp:1:20
  
  Value $80 is not valid for type nes_color.
  
  Allowed range: $00..$3F.
  

• Suggested fix: Use a hexadecimal value from $00 through $3F.

E4003 - Invalid byte value

• Category: Type System
• Explanation: A byte occupies one byte and cannot represent values above $FF.

• Trigger:

  Counter := $100;
  

• Expected compiler output:

  E4003 demo.nsp:1:12
  
  Value $100 is not valid for type byte.
  
  Allowed range: $00..$FF.
  

• Suggested fix: Use a hexadecimal value from $00 through $FF.

E4004 - Incompatible types

• Category: Type System
• Explanation: Assignments and intrinsic arguments require exact type matches. Numeric-to-boolean and other implicit conversions are forbidden. Arithmetic expressions and their operands must have type byte. Comparison operands must follow the comparison operator’s type rules, and Boolean operators require boolean operands. Increment/decrement targets and amounts, plus for control variables and bounds, must have type byte. Procedure arguments must exactly match their corresponding byte or boolean parameter types.

• Trigger:

  Counter := Active;
  

• Expected compiler output:

  E4004 demo.nsp:1:12
  
  Cannot assign a value of type boolean to variable Counter of type byte.
  
  The source and target types must match.
  

• Suggested fix: Use a source value with exactly the target type. Use true or false for a boolean literal, and use arithmetic only with byte values. Compare matching types, and use not, and, and or only with boolean values.

E4005 - Unsupported parameter type

• Category: Type System
• Explanation: The current value-parameter calling convention supports only byte and boolean. Although nes_color, sprite, and metasprite remain valid global types, they cannot be used for a parameter yet.

• Trigger:

  procedure SetColor(Color: nes_color);
  begin
  end;
  

• Expected compiler output:

  E4005 demo.nsp:1:27
  
  Type nes_color is not supported for procedure parameters.
  

• Suggested fix: Declare the value parameter as byte or boolean, or keep an nes_color value in global state.

E4006 - Invalid controller argument type

• Category: Type System
• Explanation: The controller index and button arguments describe compile-time byte values. Boolean values cannot select a port or button.
• Trigger: nes.controller_down(true, nes.button_a) or a boolean button argument.
• Expected compiler output: E4006 identifies the argument and its actual type.
• Suggested fix: Pass $01 or $02 as the controller and exactly one nes.button_* constant as the button.

E4007 - Invalid palette argument type

• Category: Type System
• Explanation: Palette and color indexes require compile-time byte values, while color arguments require nes_color. No implicit conversions are performed.
• Trigger: Pass a Boolean index or a byte variable as a palette color.
• Expected compiler output: E4007 identifies the argument, actual type, and required type.
• Suggested fix: Use a byte constant for indexes and an assigned nes_color value for colors.

E4008 - Invalid sprite value

• Category: Type System
• Explanation: A sprite is a strongly typed hardware OAM index and must select one of the NES’s 64 entries.
• Trigger: Compile tests/fixtures/diagnostics/invalid_sprite_value.nsp, or declare or assign a sprite value above $3F.
• Expected compiler output: E4008 identifies the invalid literal and the supported $00..$3F range.
• Suggested fix: Use a sprite index from $00 through $3F.

E4009 - Invalid metasprite value

• Category: Type System
• Explanation: A metasprite is an opaque static instance identity. A hexadecimal number is not a metasprite instance or symbolic frame.
• Trigger: Compile tests/fixtures/diagnostics/invalid_metasprite_value.nsp, which assigns a hexadecimal literal to a metasprite variable.
• Expected compiler output: E4009 rejects the literal without converting it to an instance identity.
• Suggested fix: Assign the result of nes.metasprite_create(imported.frame) to the variable.

E4010 - Invalid array element type

• Category: Type System
• Explanation: Fixed arrays currently support byte, boolean, or a declared record as the element type.
• Trigger: Declare array[$00..$03] of nes_color.
• Suggested fix: Use byte, boolean, or a declared record as the element type.

E4011 - Invalid array index type

• Category: Type System
• Explanation: An array index must be a strict byte expression.
• Trigger: Index an array with a boolean value.
• Suggested fix: Use an assigned byte variable, literal, constant, or arithmetic expression.

E4012 - Array index out of bounds

• Category: Type System
• Explanation: A compile-time-known index is outside the array’s inclusive declared range.
• Trigger: Read or write Values[$08] when Values is declared as array[$00..$07] of byte.
• Suggested fix: Use a constant index inside the declared bounds. Variable indexes remain the program’s runtime responsibility.

E4013 - Invalid array usage

• Category: Type System
• Explanation: A scalar was indexed, or an array was used or assigned as a whole scalar value.
• Trigger: Compile Counter[$00] := $01 or Counter := Values.
• Suggested fix: Index a declared array and read or write one element.

E4014 - Invalid array bounds

• Category: Type System
• Explanation: Arrays use a zero-based byte range with lower bound $00 and upper bound no greater than $FF.
• Trigger: Declare array[$01..$04] of byte.
• Suggested fix: Declare a range such as array[$00..$03] of byte.

E4015 - Duplicate enumeration member

• Category: Type System
• Explanation: Every member name in one enumeration must be unique.
• Trigger: Declare GameState = (Title, Playing, Title).
• Suggested fix: Rename or remove the repeated member.

E4016 - Too many enumeration members

• Category: Type System
• Explanation: Enum values are byte-sized and can represent at most 256 members.
• Trigger: Declare an enumeration with 257 members.
• Suggested fix: Reduce the declaration to 256 or fewer members.

E4017 - Invalid enumeration comparison

• Category: Type System
• Explanation: Enums expose equality and inequality, not ordinal ordering.
• Trigger: Compile State < Playing for an enum variable.
• Suggested fix: Use = or <>, or model ordered state separately with a byte if ordinal behavior is genuinely needed.

E4018 - Unknown enumeration member

• Category: Type System
• Explanation: A value expected to be a member of an enum is not declared by that enum.
• Trigger: Assign Missing to a GameState variable.
• Suggested fix: Use a member declared by the target enum type.

E4019 - Duplicate record field

• Category: Type System
• Explanation: Field names must be unique within one record, using the language’s case-insensitive name rules.
• Trigger: Compile tests/fixtures/diagnostics/duplicate_record_field.nsp.
• Suggested fix: Rename or remove the repeated field.

E4020 - Unknown record field

• Category: Type System
• Explanation: The selected field is not declared by the record type.
• Trigger: Compile tests/fixtures/diagnostics/unknown_record_field.nsp.
• Suggested fix: Select a field declared by the target record.

E4021 - Field access on non-record

• Category: Type System
• Explanation: Dot field selection requires a record variable or a record array element.
• Trigger: Compile tests/fixtures/diagnostics/field_access_on_non_record.nsp.
• Suggested fix: Remove the field selector or use a declared record value.

E4022 - Unsupported record field type

• Category: Type System
• Explanation: Record fields currently support only byte, boolean, and declared enumeration types. Arrays and nested records are not fields in this milestone.
• Trigger: Compile tests/fixtures/diagnostics/unsupported_record_field_type.nsp.
• Suggested fix: Store the nested data separately or use a supported one-byte field type.

E4023 - Recursive record definition

• Category: Type System
• Explanation: A record cannot contain itself directly. Recursive layouts have no finite static size.
• Trigger: Compile tests/fixtures/diagnostics/recursive_record_definition.nsp.
• Suggested fix: Remove the recursive field and store an explicit byte identity or index instead.

E4024 - Invalid record layout or indexed offset

• Category: Type System
• Explanation: A record is empty or exceeds the supported 256-byte layout, or a variable record-array access could require an offset above $FF and be truncated by 6502 indexed addressing.
• Trigger: Declare an empty record, a record with more than 256 one-byte fields, or variable-index a sufficiently large record array.
• Suggested fix: Give the record a supported fixed layout, reduce its size, split the array, or use a compile-time constant index.

E4025 - Invalid record usage

• Category: Type System
• Explanation: Records are static aggregates, not whole expression values in milestone 0.5.10.
• Trigger: Compile tests/fixtures/diagnostics/invalid_record_usage.nsp.
• Suggested fix: Read, assign, or compare the individual typed fields.

E4026 - Unsupported function return type

• Category: Type System
• Explanation: User functions currently return only byte or boolean; arrays, records, enums, and NES-specific handle types are not supported return values.
• Trigger: Compile tests/fixtures/diagnostics/unsupported_function_return_type.nsp.
• Suggested fix: Return a byte or boolean and store aggregate or hardware state in explicitly declared variables.

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