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diff --git a/miralib/manual/25 b/miralib/manual/25 new file mode 100644 index 0000000..6e0cef9 --- /dev/null +++ b/miralib/manual/25 @@ -0,0 +1,80 @@ +_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). + |