Comments on the syntax for Miranda scripts

The syntax equations given express the syntax of Miranda scripts insofar as this can be done by a context free grammar. It therefore does not attempt to express the scope rules, nor the requirement that a script be well-typed, both of which are context sensitive restrictions on the syntax given here. The formal definition of Miranda [in preparation] will deal with these matters and also give a denotational semantics for the language.

Nevertheless, if the syntax is read in conjunction with the informal description of the language (see other manual sections and referenced papers) it should be found fairly informative, especially if the reader has some previous exposure to this style of language.

Key to abbreviations in syntax:-

    >    alt=alternative            decl=declaration    def=definition
    >    e1=operator_expression     exp=expression      fnform=function_form
    >    libdir=library_directive   pat=pattern         qualifs=qualifiers
    >    rhs=right_hand_side        sig=signature       spec=specification
    >    tdef=type_definition       tform=typeform      var=variable
    >    whdefs=where_defs

Conventions

We use a variant of BNF, in which non-terminals are represented by lower case words, := is used as the production symbol, and alternative productions are written on successive lines. (These departures from convention are adopted because ::=' and|` are concrete symbols of the language.)

For any non-terminal x,

    x*      means zero or more occurrences of x
    x?      means the presence of x is optional
    x-list  means one or more x's (separated by commas if >1)
    x(;)    means that  x  is  followed by an optional semicolon and
    is subject to the offside rule (see section on Layout),  so  that  every
    token  of  x  must lie below or to the right of the first.  Provided the
    layout makes it clear where x terminates, the trailing semicolon may  be
    omitted.

Notes

The syntax of the library directives (denoted by the non-terminal libdir) is given in a separate manual entry.

Ambiguities in the syntax for type' andconstructare resolved by noting that->' is less binding than $typename' or$constructor` and that all three are right associative.

In connection with the productions for argtype, note that type such as [num,bool]' is an abbreviation for[(num,bool)]` and represents the type of a list of tuples - the Miranda system itself never uses this abbreviation when printing a type, but accepts it in user scripts. (Use of this abbreviation is not recommended - it will probably be removed from the syntax at the next release.)

Ambiguities in the syntax for fnform' andpatare resolved by taking into account the relative binding powers of the infix operators involved. Specifically that:is right associative and less binding than+`, which is left associative, and that $constructor, $var have a higher binding power than either of these, and are right associative.

The productions given for cases correctly describe the concrete syntax of these entities, including the way the offside rule is applied to them. This concrete syntax is in one sense misleading, however. Namely in that if a lastcase' with a trailingwheredefsis preceded by a series of alternatives, the scope of the names introduced by the where IS THE WHOLEcases' IN WHICH IT OCCURS, AND NOT JUST THE lastcase.

Note that for compatibility with earlier versions of Miranda the use of the keyword if is optional.

The ambiguities in the syntax given for e1 are resolved by taking into account the relative binding powers of the operators (see manual section on Operators).

The syntax of identifier, IDENTIFIER, literal, literal1, numeral, nat, infix, infix1, prefix, prefix1, and typevar are given under Lexical Syntax (see next manual section).