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_C_o_m_m_e_n_t_s_ _o_n_ _t_h_e_ _s_y_n_t_a_x_ _f_o_r_ _M_i_r_a_n_d_a_ _s_c_r_i_p_t_s
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
_C_o_n_v_e_n_t_i_o_n_s
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 _o_f_f_s_i_d_e _r_u_l_e (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.
_N_o_t_e_s
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' and `construct' are 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' and `pat' are 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 trailing `wheredefs' is preceded by a
series of alternatives, the scope of the names introduced by the _w_h_e_r_e
IS THE WHOLE `cases' 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).
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