%%%%%%%%%%
% move_t %
%%%%%%%%%%

move_t = cluster is create, parse, unparse, get_from, get_to, equal
    % Overview: A move provides an immutable representation for a 
    %           single piece movement.
    rep = struct[from,to:place_t]
    % Abstraction function: 
    %     A(r) represents a move on a board supported 
    %     by the place_t type, from the place r.from to the 
    %     place r.to.

    % Rep invariant: true


    create = proc(from, to: place_t) returns (cvt)
	% effects:	Returns the move from "from" to "to".
	return(rep${from:from,to:to})
	end create
    
    parse = proc(s: string) returns (cvt) signals (invalid)
	% effects:	Returns the move represented in the form "a1-b2" 
	%    		by s. the column letter can be either an upper 
	%		case or lower case letter Signals invalid if the 
	%		format is not valid for a move.
	if (string$size(s) = 5) & (string$fetch(s,3) = '-') then
	    begin
		from : place_t := place_t$parse(string$substr(s,1,2))
	    	to : place_t := place_t$parse(string$substr(s,4,2))
		return(rep${from:from,to:to})
		end 
	    resignal invalid
	    end
	    signal invalid
	end parse
    
    unparse = proc(m: cvt) returns (string)
	% effects:	Returns the textual representation of the move, 
	%		i.e., "a1-b2", the column character will be a 
	%		lowercase letter. 
	from_str : string := place_t$unparse(m.from)
	to_str : string := place_t$unparse(m.to)
	return((from_str || "-") || to_str)
	end unparse
    
    get_from = proc(m: cvt) returns (place_t)
	% effects:	Returns the place to be moved from.
	return(m.from)
	end get_from
    
    get_to = proc(m: cvt) returns (place_t)
	% effects:	Returns the place to be moved to.
	return(m.to)
	end get_to
    
    equal = proc(m1,m2:cvt) returns(bool)
	% effects:	Returns true if m1 and m2 represent the same 
	%		chess move.
	return((m1.from = m2.from) & (m1.to = m2.to))
	end equal
    
    end move_t