MLton 20210117

# MLBasisAnnotations

ML Basis annotations control options that affect the elaboration of SML source files. Conceptually, a basis file is elaborated in a default annotation environment (just as it is elaborated in an empty basis). The declaration ann "ann" in basdec end merges the annotation ann with the "current" annotation environment for the elaboration of basdec. To allow for future expansion, "ann" is lexed as a single SML string constant. To conveniently specify multiple annotations, the following derived form is provided:

ann "ann" ("ann" )+ in basdec end ⇒ ann "ann" in ann ("ann")+ in basdec end end

Here are the available annotations. In the explanation below, for annotations that take an argument, the first value listed is the default.

- allowFFI {false|true}

  If true, allow _address, _export, _import, and _symbol expressions to appear in source files. See ForeignFunctionInterface.

- allowSuccessorML {false|true}

  Allow or disallow all of the SuccessorML features. This is a proxy for all of the following annotations.

  - allowDoDecls {false|true}

    If true, allow a do exp declaration form.

  - allowExtendedConsts {false|true}

    Allow or disallow all of the extended constants features. This is a proxy for all of the following annotations.

    - allowExtendedNumConsts {false|true}

      If true, allow extended numeric constants.

    - allowExtendedTextConsts {false|true}

      If true, allow extended text constants.

  - allowLineComments {false|true}

    If true, allow line comments beginning with the token (*).

  - allowOptBar {false|true}

    If true, allow a bar to appear before the first match rule of a case, fn, or handle expression, allow a bar to appear before the first function-value binding of a fun declaration, and allow a bar to appear before the first constructor binding or description of a datatype declaration or specification.

  - allowOptSemicolon {false|true}

    If true, allows a semicolon to appear after the last expression in a sequence expression or let body.

  - allowOrPats {false|true}

    If true, allows disjunctive (a.k.a., "or") patterns of the form pat | pat.

  - allowRecordPunExps {false|true}

    If true, allows record punning expressions.

  - allowSigWithtype {false|true}

    If true, allows withtype to modify a datatype specification in a signature.

  - allowVectorExpsAndPats {false|true}

    Allow or disallow vector expressions and vector patterns. This is a proxy for all of the following annotations.

    - allowVectorExps {false|true}

      If true, allow vector expressions.

    - allowVectorPats {false|true}

      If true, allow vector patterns.

- forceUsed

  Force all identifiers in the basis denoted by the body of the ann to be considered used; use in conjunction with warnUnused true.

- nonexhaustiveBind {warn|error|ignore}

  If error or warn, report nonexhaustive patterns in val declarations (i.e., pattern-match failures that raise the Bind exception). An error will abort a compile, while a warning will not.

- nonexhaustiveExnBind {default|ignore}

  If ignore, suppress errors and warnings about nonexhaustive matches in val declarations that arise solely from unmatched exceptions. If default, follow the behavior of nonexhaustiveBind.

- nonexhaustiveExnMatch {default|ignore}

  If ignore, suppress errors and warnings about nonexhaustive matches in fn expressions, case expressions, and fun declarations that arise solely from unmatched exceptions. If default, follow the behavior of nonexhaustiveMatch.

- nonexhaustiveExnRaise {ignore|default}

  If ignore, suppress errors and warnings about nonexhaustive matches in handle expressions that arise solely from unmatched exceptions. If default, follow the behavior of nonexhaustiveRaise.

- nonexhaustiveMatch {warn|error|ignore}

  If error or warn, report nonexhaustive patterns in fn expressions, case expressions, and fun declarations (i.e., pattern-match failures that raise the Match exception). An error will abort a compile, while a warning will not.

- nonexhaustiveRaise {ignore|warn|error}

  If error or warn, report nonexhaustive patterns in handle expressions (i.e., pattern-match failures that implicitly (re)raise the unmatched exception). An error will abort a compile, while a warning will not.

- redundantBind {warn|error|ignore}

  If error or warn, report redundant patterns in val declarations. An error will abort a compile, while a warning will not.

- redundantMatch {warn|error|ignore}

  If error or warn, report redundant patterns in fn expressions, case expressions, and fun declarations. An error will abort a compile, while a warning will not.

- redundantRaise {warn|error|ignore}

  If error or warn, report redundant patterns in handle expressions. An error will abort a compile, while a warning will not.

- resolveScope {strdec|dec|topdec|program}

  Used to control the scope at which overload constraints are resolved to default types (if not otherwise resolved by type inference) and the scope at which unresolved flexible record constraints are reported.

  The syntactic-class argument means to perform resolution checks at the smallest enclosing syntactic form of the given class. The default behavior is to resolve at the smallest enclosing strdec (which is equivalent to the largest enclosing dec). Other useful behaviors are to resolve at the smallest enclosing topdec (which is equivalent to the largest enclosing strdec) and at the smallest enclosing program (which corresponds to a single .sml file and does not correspond to the whole .mlb program).

- sequenceNonUnit {ignore|error|warn}

  If error or warn, report when e1 is not of type unit in the sequence expression (e1; e2). This can be helpful in detecting curried applications that are mistakenly not fully applied. To silence spurious messages, you can use ignore e1.

- valrecConstr {warn|error|ignore}

  If error or warn, report when a val rec (or fun) declaration redefines an identifier that previously had constructor status. An error will abort a compile, while a warning will not.

- warnUnused {false|true}

  Report unused identifiers.

## Next Steps

- MLBasisAnnotationExamples

- WarnUnusedAnomalies