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SpecSyntax.md

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Syntax of Smopeck Spec Language

Top Level Definition

<TopLevelDef> ::= <TypeDef> | <EndpointDef>

Type Definition

<TypeDef> ::= 'type' <TypeName> '=' <TypeExp>
<TypeExp> ::= <TypeName> <BindAs>? <TypeExtension>? <TypeRefinment>? 
            | <Literal> 
            | <TypeExp> '|' <TypeExp>  -- Union type
            | <TypeExp> '&' <TypeExp>  -- intersection type
            | '(' <TypeExp> ')'

<TypeName> ::= r"[A-Z][A-Za-z0-9]*"
<TypeExtension> ::= '{' <TypeBindingList> '}'
<TypeRefinment> ::= '[' <RefineList> ']'

<BindAs> ::= '@' <LowerId>

<TypeBindingList> ::= <TypeBinding> (',' <TypeBinding>)*


<TypeBinding> ::= <BindingKey> ':' <TypeExp>
<BindingKey> ::= r"[a-z][A-Za-z0-9_\-]*"

<Literal> ::= <DQStringLiteral> | <SQStringLiteral> | <BooleanLiteral> | <NumberLiteral> | <RegexLiteral>
<RefineList> ::= <RefineExp> (',' <RefineExp>)*
<RefineExp> ::= '.' <CompOp> <Exp>
<RefineAtom> ::= <RefineVar>('.' <Accessor>)* | <Literal>
<Accessor> ::= (<TypeName> '#')? <BindingKey> | 'get(' <Exp> ')'

Endpoint Definition

<EndpointDef> ::= 'endpoint' <EndpointPath> <Method> <TypeExtension> 
<EndpointPath> ::= Double quoted String Literal
<Method> ::= 'GET' | 'POST' | ...

Conditional Types

You can write conditional type with the following syntax.

<TypeExp> ::= <TypExp> '?' <Exp>

ty ? e is read as "this type accepts a value of ty if the condition e is true, and otherwise this type has no inhabitans".

Optional Fields

Optional fields for objects are written with the following syntax.

<OptionaAssoc> ::= <Field> '?:' <TypeExp>

For example,

Object @ obj{
    intField : Int
    optionalField ?: Object {
        key: String,
        size: Int,
        ord: 'asc' | 'desc'
    }
}

Optinal fields are accessible with the following accessors obj.optionalField?.key. This will introduce monadic computation. In monadic computation, optional failures are ignored.

For example Int[ . > obj.optionalField?.size ] is equal to Int [ . > 10 ] for object { optionalField : { size : 10 }}, and is equal to Int [] if optinalField is not set.

You can set default value for optinal computation with ?> operator. Int [ . > (obj.optinalField?.size + 1) ?> 3 ] is equal to Int [ . > 4 ] if optinalField is not set.