apple-pascal-1.3-manual

IMPLEMENT A TI ON keyword; it is possible that only one block of this pagemay be produced if the IMPLEMENTATION keyword occurs in the firstblock of the page. Valid data in each page of a textfile end with a CR(ASCII 13) followed by at least one NULL (ASCII 0).The ten characters immediately following the IMPLEMENTATION keywordcontain special unit information. All ten characters are ASCII spaces,except for an E in the ninth position required by the Pascal Compiler andLIBRARY programs to terminate the interface text. AP may occur, insteadof a space, in the second of the ten character positions to signify to thePascal Compiler that the unit requires the PASCALIO standard ProgramUnit. The fourth position will be occupied by an L if the unit requires theLONGINTIO standard Program Unit. These items-IMPLEMENTATION, P,L, and E-are all considered tokens by the Compiler; thus, their order issignificant, but their spacing and case are not.Interface text is not stripped of nonprinting characters or comments.Leaving the comments in the interface text produces more completeinternal program documentation at the expense of increased codefile length.IBy the Way: The interface text of Program Unit segments is used onlyduring compilation. Thus it can be removed from completed codefiles thatwill only be executed. The effect is a reduction in codefile size.The TEXT AD DR array of the segment dictionary contains pointers to thestarting address of the interface text for each segment. The pointers specifyblock numbers, relative to the start of the codefile. The field is 0 forsegments that are not Program Unit code segments, as well as Program Unitsegments that do not have an interface part.Code PartsThe code part of a code segment consists ofo Code for a group of up to 254 procedures;o A procedure dictionary, containing information about the procedures.Figure 2-6 is a diagram of the code part of a code segment. Each code partcontains the code for the highest level procedure in the segment, as well asthe code for each of the non-SEGMENT procedures and functions withinthe segment. The code of the highest level procedure, which is generatedlast, appears highest in the code part.IV-30Chapter 2: Disk Files