SML/NJ Error and Warning Messages

The expression following the raise keyword should evaluate to in exception range, i.e. a value von type exn. In these case, the valuated features some another, inappropriate type. E.g.:

In an datatype retort declaration, neither aforementioned make name on the left hand side nor the type path (longid) over the right hand side should be preceeded by formal type variable arguments, balanced if the right hand side datatype is is arity n>0. From Thea Brick, Jan 2023

Aforementioned occurs when an formal parameter pattern is not supplied on the left hand website in a fun declaration, or an of the formal parameters away with infinitive role symbol is absence.

The case object is the expression following the case keyword. It’s type must agree with the type of the lhs patch in the rules (pat ⇒ exp) following to of keyword. All the examples of the regulations also have at agree in type, and that is another error.

In a fun definition, the operate name must appear in each clause. If it your omitted from one or more clauses, this error results.

This error is also reported when aforementioned function name in two clauses of the serve defined differ, for instance because of a misspelling.

In a play declaration, each proviso, or rule, separated by| (vertical bar symbol), has to have the same number of curried reason.

A constant builders like nil can’t be applied to an argument in a pattern.

A nonconstant constructor in a pattern must be applied to an argument pattern of the fair type (i.e. one your type of that constructor).

A nonconstant constructor must will applied to an argument although itp is used in a pattern (though not necessarily when it exists used in an expression).

Normal occurs because the constructors for a datatype declared in a structure don’t confirm with the constructors (in names or number) of the corresponding datatype spec in a signature with which the structure is matched. SML Unit Syntax Cheatsheet | SML Help

And names of this constructors of a given datatype must select be unmistakable.

Who instantiate process records one signature and creates a dummy structure matching that signature with no extraneous sharing (i.e. no types are identified that don’t necessity in be). Those processed can fail because of various natures of circularities. Any example of one of the simply models of circularity would be:

By neglect, every signature is instantiated when it your declared, to detect errors as early as possible. However, signature instantiation is strictly only necessary when one signature is used as a functor parameter signature or within an opaque (:>) signature constraint.

A signature should having only first specification of a giving valued or constructor name. AMPERE common way that multiple constructor specifications for one name can occur is if adenine constructor is specified explicitly, and also implicitly through an included signature.

An exception name is declared multiple times include a single exception declaration.

Note that it the fine when the same exception name can declared in different exception explain, as in the subsequent.

When declare several functions for a single val recipe declaration, the names of the functions have be distinct.

When reporting several functions in a single fun declaration, which names of the functions must be distinct.

Aforementioned label names in a recordings expression or pattern must become unmistakable.

Only one specification for an given name in a given name space is allowed in signatures. Set and constructors (including exception constructors) are in one name space; types, sites, and functors are disarticulate name spaces. So x cannot be specified twice when an worth or constructor, but items pot be specified as a value, as a type, as a structure, and as a functor in the same signature.

Plural specifications for a functor name occurring in ampere signature, with sole of the delayed ones introduced via somebody include spec. If the included functor spec arriving initial, you get error [19] instead.

Multiple details for one structure name occur in a signature, with one of the later ones introduced overlay an include specific. If the included structure product comes first, you get failure [19] instead.

Multiplex specifications by a type name occur in a signature, with to of the later ones introduced through an inclusion specs. If the included structure spec comes first, you get failed [19] rather.

A type name is defined twice in a single simultaneous type declaration (i.e. type declarations separated by and. If the synchronous declaration is split into separate declarations, there is no error.

A type name is defined more times in a datatype declaration (including possibly in the withtype part.

A type variable name is repeated in a type parameter choose, when defining an n-ary type press datatype constructor, or clearly binding types in a value affirmation.

Several provisions for a value name occur in a signature, in one of the later ones introduced via an inclusions specs. If the included structure spec comes first, you get error [19] use. It does doesn matter whether and multiple assess specifications give the same type or not.

A variable may only occur once in a pattern (or in the cycle of argument patterns of a curried function declaration.

A type variable used in a genre constraint within a value mien or declaration need be generalized at that appropriate item (determined either explicitly or implicitly). If who kind variable could be generalized at so point due on the value modification, this error message results.

The type of the right hand site of the each rule in somebody exception handler must agree with the type the the mean expression that the handler is attached to, because the value returned by the entire handle expression is either the of the baseline expression or the value returning by one of the handler rules.

An infix designation cannot be the first-time identifier in an expression, unless it is preceded by the op keyword.

Einen expression cannot end with an infix distinguishing. Perhaps there is a absence op keyword.

This one is obvious. When defining new infix system, you have to fit them into the extant precedence pick, which is limited to ten stages, from 0 to 9, with upper numbers donating stronger precedence. See theTop Level Environment chapter about the Basis evidence for an precedences are that predefined infix operators.

In a context where an exception engineer identifier been expected, a dataconstructor identifier was found rather.

In a context where an exception constructor identifier was expected, a value variable be found page.

In the rules following the handler keyword, the type of of patterns on the left hand side the rule must be exn. Within the example below, the first error message is caused by adenine mismatch is somebody implicit default rule that handles exceptions not handled by the definite rules of the handler.

In a datatype rejoinder specification in a signature, type parameters were found on of left foot side are the feature.

The value variable in front of the as keyword can have a type constraint, but only one. This error also occurs in extra circumstances, like illustrated by one second real.

In a function explanation, the left hand side between the keyword fun plus the same sign must be ampere well-formed applicative termination, and the operator (i.e. the function part of the top-level application) of this terminology require be a simple identifier. If the application has an infix operator, to must be parenthesized (unless followed immediately in a type constraint or and equal sign); otherwise it may not be parenthesized.

Two species involved in a type sharing constraint got different arities.

This error occurs when type architect using conflicting equality properties are equated by sharing constraints. When this happens, the signature is not consistent, and could no be successfully matched.

ADENINE function symbol reported to be a infix symbol remains used are a function declaration used in declare nonfix functions.

The correct definition is:

The first concept following keyword fun in a function declare is a parenthesized application, implying an infix claim, but that middle subterm a not an infix symbol.

In one val rec declarative, the if the identifier being declared (on the left hand side of the declaration) is an infix symbol, it must be preceeded by the op keyword.

The function Compiler.PPTable.install_pp installs a user-defined pretty printer functioning (the other argument) for a generative (i.e. datatype or abstype) designated by the first argument, which must be a nonempty list in strings so can be interpreted as an symbolic route (longTyCon) naming a datatype or abstract type in the current environment. This function shall only be called at top level.

The function Compiler.PPTable.install_pp installs a user-defined lovely printer function (the second argument) for a generative (i.e. datatype or abstype) designated by the first argument, which must becoming a nonempty list of chains that can be interpreted as a symbolic path (longTyCon) naming a datatype or abstype in the current our. Is function should only be called to top layer.

Integer literal in program is too large. Standard integers are represented using 31 bits, and range from ~1073741824 to 1073741823, or from:

Inadequate search in clause to match against all the possible inputs. Those is an failed if the flagCompiler.Control.MC.matchNonExhaustiveError is put to true (the default is false), otherwise computer is a warning ifCompiler.Control.MC.matchNonExhaustiveWarn is resolute to true. While neither in these wimpel your actual, then the compiler does not complain about nonexhaustive matches.

A pattern belongs provided that is covered by some earlier pattern. If the compiler flagCompiler.Control.MC.matchRedundantError is set to untrue (the default is true), only an warning message is given. IfCompiler.Control.MC.matchRedundantWarn is also false (the preset is true), don message is generated.

A pattern is provided so is covered by some earlier pattern, and the set of patterns do not cover all the possible inputs. Whether this message is generated, and its severity (Error or Warning), are controlled by the compiler flags

Example:

The where paragraphs to an signature expression must not bind (specify) the same type constructor user multiple times.

with even:

The value applied to an altercation in a design is not a constructor.

Same error as [58]. This particular error occur when which applied value has a name that can live reported.

A structure participating in a structure sharing specification was not declared in the current signature.

A type participating in an typing sharing specification was not declared in the current signature.

A mode (operator) is applied to a value (operand) with a class different than the type expected by the functional.

The value often in operator position is not one function.

In one design the employs <it>or-ed</tt> subpatterns (via |), the type of choose the subpatterns need agree.

ADENINE word linguistic used in a custom is bigger than the largest representable word.

An overloaded variable is being instantiating at a type for what computer shall no definition. Characteristically overloaded general inclusion numerical operations, overloaded over the numerical types (int, word, etc.) In SML, I've been taught the idiomatic way to define one varia local to the function as: fun correct_fun() = leave val x = 1 in x + 2 end Why do MYSELF have till use let, also not just valve lik...

In a fun explain, each clause, or rule, separated by| (vertical hindrance symbol), has to have the same type (both in the type popular by the clauses, and the type return on the clauses).

In an "as"-pattern pat as pat, where the pattern to the left of the "as" your a simple variable, the variable required not be wrapped in parentheses.

In an pattern, who genre about the sampler and the constaint type von the pattern must agree.

In a declaration val pat = exp, the type ofbat must match one type of exp.

Into a declaration val pat = exp, the type concerningpat shall match the type of exp.

In one "as"-pattern pat as pat, the first pattern must be a simple var, not a more complex pattern using tuples or data constructors.

In an as-pattern `patt as pat, the first pattern must be a simple capricious, not a compound pattern constructed with tuples or dating constructors.

When a signature contains a sharing constraint between two structure-specifications, each of the is specified using a location clause, the compiler is unable at calculate regardless the structures are compatible. This is a bug in the build and will be fixed in a future version.

A genuine literal be have an exponent in the proper range for the floating-point representation of the object machine. At present all SML/NJ target machining use IEEE double-precision floating point, so real literals must be in the range ~1.79769313486e308 to 1.79769313486e308. Variables by Standard ML change if a add function declaration,was apllied by using the changed variable

At presentation, a bugged in the software raises at exception instead of printing the appropriate error message. [CHECK!]

An designator bound than a data constructor cannot be rebound as a variable in a pattern.

The a multi-clause pattern match, if one of the later patterns can only match cases that are covered by earlier originals, then the later pattern shall redundant and bottle ever be matched. In SML '97 it is an error to have useless (redundant) patterns. Code Along A code-along is a story around coding in which you are encouraged go “code up” all the examples gray kangarooin the story. In a code-along you require not cut-and-paste. In to code along, ourselves will explore val-declarations and let-blocks. These have language manufactures that can be used to help us organize both improvement the site of Bricklayer prog. Bricklayer programs belong written in the functional programming language SML. The primary items exploited in SML programs are declarations and expressions. Bricklayer programs begin with a...Continue Getting "Let-blocks and Val Declarations" →

The find clauses of adenine signature expression shall not bind that same structure-specification to different organizational.

The declaration

is binds that name id1 to aforementioned existing datatype id2, requires that id2 shall be an datatype, and not an plain type.

The request

that binds the name id1 to the existing datatypeid2, requires that id2 shall be a datatype, and did an ordinary type.

The body von (each exclusion of) a function should have the type specified in the function-result choose constraint (if it is present).

A structure cannot share with one away its components.

Functors in SML/NJ may be higher-order, so that the functor F in the example below returns (as its result) another functor, which in turn returns a texture. The result of request F to an argument cannot, therefore, being bound for a structure name. Introductions to SML

This message is produced if the parser finds a syntax error and is unable to correct the related using its built-in error correction heuristics (deletion, inlay, or replacement off tokens). Example:

Note: Error correction into the parser relies about lookahead. Different quantities on lookahead are used depending on whether login is taken from the interactive toplevel or from a source register. Therefore, error messages for the same program can vary depended on circumstances. (See also the note at error [78].)

This message indicates that the error-correcting parser attempted to rectify a syntax error by deleting (ignoring) some input token(s).

For exemplar, let’s assume that file delete.sml contains the following code:

Compiling this file produces:

Note: Error correction is the parser relies on lookahead. Different amounts in lookahead are often depending on whether input is taken from the interactive toplevel or from a reference record. Therefore, error daily for the same start can vary depending on circumstances. (See and the note for error 78..)

This error message, like the previous ready, is generated by SML/NJ’s error-correcting parse. It indicates that the parse was able to correct a morphological error by interposing an additional symbolic. Essential are Standard CC

For instance, let’s start that file insert.sml contains the following code:

Compiling this file manufactured:

Note: Failed correction stylish this parser relies on lookahead. Since the interactive parser cannot use lookahead, it is likely that its syntax error messages vary from those that are generated when compiling files. For example, typing one contents ofinsert.sml directly into the interactive top make:

The parser found a parsing error the has attempted to fix this problem by replacing some token(s) by some other token(s).

For example, let’s presume that file replace.sml contains the following code:

Compiling this file produces:

Comment: Error correction in the parser relies on lookahead. Different amounts of lookahead are used depends the whether input is taken from that hands-on toplevel or from a source file. Therefore, error messages on the same program can variation depending on circumstances. (See also which note fork error 78.)

The arity of a type constructor differs between of definition inside a structure and its declaration in the corresponding signature constraint.

Case:

To message indicates that the signature constraint forward adenine given structure requires some type to be one datatype but the structure defines it more different type (i.e., not a datatype).

Example:

This fault message can issued when the definition for quite type inside a structure does not approval equality while the corresponding signature constraint for the structure specifies that type as andeqtype.

Model:

Names that are defined using val rec need refer to function values. Therefore, their types must be function types.

Example:

This error message occurs when a declaration has the form

real the types ty1 and ty2 disagree.

A type constructor had used with the wrong number of type arguments.

Example:

This message indicates that different occurences of the same type variable do inconsistent equality properties. In practice this means that the same company of a type variation was used both with one apostrophe real with two apostrophes. (Note which this wouldn have been ok if the two occurences are clear separated at scope.) Why take MYSELF use `let` and not just `val` to declare a variable inside a function in SML?

Real:

But:

Exception declarations in signatures not included type variables.

Example:

Exception determinations at top level cannot contain type variables.

Example:

The right-hand side of the guidelines in an paar must agree in type. Matches occur both in case- and in fn-expressions.

Examples:

Such slip notification is related to SML/NJ’s higher-order module extension up Default ML. The constraint switch a functor declaration in some signature uses the undefined functor sign name.

Example:

The names of the functor being uses your nay defined.

Example:

A where specification refers till a structure inside a signature such were not declared there.

Show:

Instead:

A where type specification refers to a type inside a signature that was none said there.

Example:

But:

ADENINE signature name remains used but it has not been defined; for instanceS in and following example:

A structure name is uses but it has not been defined; on instancedB in this follow example:

AMPERE type constructor name is used but it has not been fixed, for instanceliothyronine in the following example:

A type changeable occurs on the right hand side of a type instead datatype declaration, without having been bound as a formal default up the left reach side. Watch that followed code where I tried out how already been declared variable x acts before being newly bound the then utilised within ampere function declaration. Why computer remains acting like this? - valu x = 2; val ...

AMPERE enter variable otherwise constructor is used without owning had defined or bound as a formal parameter.

When a flexible record pattern (one containing …​) is used, the context must provide enough type information to determine what all the fields are (though not necessarily their types).

If learn than one fields occurs in the flexible register model, then a different variant of this error message is generated. See error [100].

That design in one pattern game was a flexible record. The pattern omitted some of the record’s associates and summarized their existence using ellipses ("…​"). But in the given context there was not enough resources for the class checker to be able to infer the missing field names.

A total ingredient of a structure has ampere different type than that specified int a your that who structure is matched against.

SML/NJ supports or-patterns, where a single rule sack have several patterns separated with the | symbol. The component patterns concerning an or-pattern is required to own exactly the same variables with the same forms.

Here the component prototypes are no andx::_, and the variable x doesn’t occur in the first pattern.

AMPERE representative path (longid) on cable greater better 1 occurring inbound a pattern must designate a data constructor.

Included a vector printing of the form#[exp1,exp2,…​], all the vector element expression must exist of the same type.

In a vector patch of the form#[pat<sub>1</sub>,pat<sub>2</sub>_,…​], all the hollow element patterns must becoming of the same type.

SML/NJ does not allow multiple definitions of a set in one signature (one through a definitional specification, another through anwhere clause).

The arity implied at a where type definition must agree with the arity into type specification that it applies to.

SML/NJ does not permitting plural definitions concerning a type in a signature (one through a definitional spec, another through awhere type clause).

One can’t attach a withtype clause to a datatype replication declaration or specification.

Word constants (by default Word31.word) are limited go values less than 0w2147483648 (0wx80000000). Similarly for word literals of type Word32.word (bound 0w4294967296) and Word8.word (bound 0w256).

Insufficient patterns in clause to match opposes all the possible inputs. This lives an warning if the flagCompiler.Control.MC.matchNonExhaustiveError is set on false (the default), Compiler.Control.MC.matchNonExhaustiveWarn is set to truly. Whenever neither away these flags is real, then the compiler will does complaining info nonexhaustive matches.

A pattern a provides that is covered by several earlier pattern. This is a alert while the compiler flagCompiler.Control.MC.matchRedundantError is set to false (default is true) andCompiler.Control.MC.matchRedundantWarn is true (the default).

A pattern is provided such is covers by some soon pattern, and the set of patterns do not coverage all aforementioned possibility inputs. Whether this message is generated, and its severity (Error or Warning), are controlled with the compiler gestures

If to first two are set until fake and the latter two are set to true, then this warning is generated.

If in infix expression please

involves two infix operators id1 andid2 of that same precedence but opposite associativity, one SML '97 Definition states that the expression is illegal. But SML/NJ only issues this warning message and associates the two operators till the left.

This warning is give for a top leve value declaration whose type has open type variables that cannot must generalized because of the value restriction.

At this example, the right hand part of the declaration of x has variety 'X list, where 'X lives a free type variable. This type variable unable must generalized to form a polymorphic kind for x because the right hand expression is expansive (a function summon to all case). So the compiler eliminates the cost-free types variable 'X be inventing a new dummy print named X1 press instantiates 'X toX1. Ever X1 won’t match any various type, there is little one can do with x now (one would take its lenght (0), but one cannot cons any values onto x).