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ALED - Ada Line Editor A Line-Oriented File Editor written in Ada by Richard Conn Texas Instruments Advanced Computer Systems Lab Ada Technology Branch 10 December 1984 C O N T E N T S 1. INTRODUCTION...............................................1 2. USING ALED.................................................2 2.1. PRELIMINARIES.........................................4 2.1.1. LINE RANGES....................................4 2.1.2. LINE REFERENCES................................5 2.1.3. STRINGS and LINES..............................5 2.1.4. INPUT LINE EDITOR..............................6 2.1.5. ABORTING COMMANDS..............................6 2.2. COMMANDS..............................................6 2.3. SAMPLE SESSION........................................9 3. SYNOPSIS and COMMENTS.....................................19 Index.....................................................20 ALED - A Line-Oriented File Editor Written in Ada ALED - Ada Line Editor A Line-Oriented File Editor written in Ada by Richard Conn Texas Instruments Advanced Computer Systems Lab Ada Technology Branch 10 December 1984 1. I N T R O D U C T I O N ALED is a relatively simple line-oriented file editor which is written in the Ada (trademark, United States Department of Defense) programming language. It was written to satisfy the following needs: (1) to help the author learn the Ada language by writing a useful program whose scope (at a few thousand lines) is reasonable (2) to help others wanting to learn Ada by providing a "living example" of an editor written in Ada (note that this example is by no means perfect and there is room for improvement) (3) to make a transportable editor, written in Ada, available for use on a variety of machines; efforts were made to use only TEXT_IO for support, so the code should be transportable between all machines that have a validated Ada compiler This document is divided into two parts: (1) an overview on the operation of the editor from the user's perspective and (2) a synopsis of what was learned during its design and comments on the design in general. The version of ALED which has been released to the Ada Repository is the Engineering Development Model (EDM) of ALED. An Advanced Development Model, which was completed some time ago and will never be released, was written to learn the basics of the problem and to prove that the problem could be solved. The EDM is a more elaborate, complete, and better-documented production of the ADM concept. A production model of ALED may be released as some future date, but no obligation is assumed on the part of the author to do so. 1 ALED - A Line-Oriented File Editor Written in Ada 2. U S I N G A L E D ALED was designed and implemented on a Data General MV10000 under the ROLM Ada Development Environment. It is invoked on this system by typing X EDITOR where EDITOR.PR is the name of the file containing the object of ALED after compilation and linking. This invocation results in the following banner being displayed: ALED - Ada Line Editor by Richard Conn, Version 1.0 File Name? The user is expected to enter the name of the file to be edited at this time. A file name must be specified, and one will be created if the file does not exist. If the indicated text file exists, its contents will be read into a doubly-linked list created by ALED and made ready for editing. Input line editing (see the following section on the Input Line Editor) is allowed, so the user can correct any errors he makes while typing the file name. After the indicated file is read in or created, ALED prompts the user with n> where "n" is 0 if there are no lines in the file (the file is empty) or 1 if there are lines in the file. The number in front of the ">" character is the number of the current line. As the user moves through the file, this number will be updated each time the prompt appears. Once this prompt appears, ALED uses single-character commands with command completion and prompting to interface to the user. In response to any one of the single-character commands recognized by ALED, the ALED editor will complete the text of the command, prompt the user for input parameters (allowing him to abort by providing no input in most cases), and then perform the function of the command. ALED is interactive in nature, and the learning curve for ALED is quite short. Built-in summary documentation is provided by means of the H (Help) command; to illustrate, when the letter "h" is typed (case is not significant on letter commands), the following display is presented: 2 ALED - A Line-Oriented File Editor Written in Ada 0> help --- Movement Commands --- ----- Enter Lines ----- + Advance N Lines A Append after <line> - Back Up N Lines I Insert before <line> F Find <string> in <range> J Jump to <line> ----- Print Lines ----- N Find Next <string> . Print Current Line ----- Delete Command ----- < Print Next Line D Delete lines in <range> > Print Next Line L List over <range> ---- Help and Exits ---- H This Help Text ---- Substitution ---- Q Quit without Updating S String Substitute X Exit and Update over <range> ---- File Get/Put ---- -- Miscellaneous -- G Get <file> after <line> ? Print Statistics P Put <file> over <range> <Range>: % %,% First or Second Entries -- #-Number, .-Current, C-Current, F-First, L-Last Singular Entries -- A-All, P-Page 0> -- Figure 1: ALED Help Command and Display -- To reiterate, the above display was generated as follows: 1) the prompt "0>" was printed by ALED 2) the user typed the letter "h" 3) the characters "elp" were filled in by ALED after the letter "h" (forming the word "help") 4) the command summary was printed by ALED 5) the prompt "0>" was again printed by ALED, indicating that it is ready for the next command 3 ALED - A Line-Oriented File Editor Written in Ada 2.1. PRELIMINARIES 2.1.1. LINE RANGES Several of the ALED commands, such as List and Find, perform their operations over a range of lines. They prompt the user for this line range with the herald "<range>". Examples of this prompt are: 1) list lines in <range> 2) find <string> over <range> 3) substitute for old <string> new <string> over <range> Whenever the range prompt ("<range>") is presented, the user may enter any of the following responses: Response Meaning -------- ------- A or a All Lines P or p Current Page (next 20 lines) . or C or c Current Line F or f First Line L or l Last Line #,# A pair of line numbers, like "5,8", or relative line references, like "-5,+10" for 5 lines before the current line to 10 lines after the current line, or any combination, like "5,+10" for line 5 to 10 lines after the current line; the only restriction is that the first number must evaluate to be less than the second number s,s A mixture of the symbols for Current Line, First Line, Last Line, and a line number or relative line reference, like ".,L" for current line to the last line, "1,." for line 1 to the current line, "F,." for first line to the current line, "-5,." for five lines before the current line to the current line, etc. 4 ALED - A Line-Oriented File Editor Written in Ada Examples: list lines in <range> A <-- all lines list lines in <range> .,L <-- current to last list lines in <range> 1,5 <-- lines 1 to 5 list lines in <range> -5,+6 <-- 5 lines before the current line to 6 lines after the current line list lines in <range> P <-- next 20 lines list lines in <range> F,L <-- same as All lines 2.1.2. LINE REFERENCES Some commands operate only on a specific line, such as the Append and Insert commands. The user is to indicate a specific line, as opposed to a range of lines, in response to the "<line>" herald printed by these commands; for example: append after <line> insert before <line> Any of the forms indicated above may be used to define this line reference, and the indicated line becomes the first line of the range. For instance, if "A" (all lines) is the response to the herald, then line 1 is the indicated line since all lines references line 1 to the last line. It is usually safer to reference only one line in response to the "<line>" herald (like, "5" or ".") rather than to use a range specification. 2.1.3. STRINGS and LINES Some commands accept a string or a line as input, such as the Substitute and Insert commands. In both cases, the text which is input by the user is simply a group of characters. No quotes or other delimiters are necessary. However, AT LEAST ONE CHARACTER MUST BE INPUT. The response may not simply be a strike at the RETURN key; a space followed by a strike at the RETURN key is the recommended combination. The reason for this restriction is discussed later. When inputting a group of lines via the Append or Insert commands, the lines are prompted for with the herald: n: where "n" is the number of the line that is about to be input. The user may enter characters as he desires in response to this prompt, remembering that blank lines consist of a space followed by the RETURN key. To terminate input, the user enters a single dot (".") followed by RETURN. See the sample session below and experiment with the editor itself for clarification. 5 ALED - A Line-Oriented File Editor Written in Ada 2.1.4. INPUT LINE EDITOR The user has the ability to edit his string or line inputs as he enters each character. This is done by striking any one of the three input line editor command characters. The following table summarizes these characters, giving their default values and the functions they perform. Default Value Function ------- -------- ` Delete previous character @ Delete all previous characters and restart input ~ Retype the line or string entered so far These default values may be changed to some other values by editing the source code and changing three constants. It may be of value to replace these defaults with more convenient values, such as the DEL key to delete the previous character, ^U to delete all previous characters, and ^R to retype the line or string. See Part 2 for an explanation of why these defaults were chosen. 2.1.5. ABORTING COMMANDS If the user strikes a command by accident, most commands may be aborted by simply doing the following: 1) not specifying a range of lines (enter a space followed by a RETURN in response to the <range> herald) 2) not specifying a line (enter a space followed by a RETURN in response to the <line> herald) 3) not specifying a file name for the Get and Put commands (enter a space followed by a RETURN) 2.2. COMMANDS The following presents the various commands of ALED. The sample session illustrates their use. COMMAND: . FUNCTION: Print the current line The "." command prints the current line. COMMAND: < FUNCTION: Back up to the last line and print it The "<" command backs up to the last line and prints it. COMMAND: > FUNCTION: Advance to the next line and print it The ">" command advances to the next line and prints it. 6 ALED - A Line-Oriented File Editor Written in Ada COMMAND: + FUNCTION: Advance n lines from the current line The "+" command moves the user an indicated number of lines forward from his current position. COMMAND: - FUNCTION: Back up n lines from the current line The "-" command moves the user an indicated number of lines backward from his current position. COMMAND: ? FUNCTION: Print statistics The "?" command prints the name of the file being edited and the number of lines in the edit buffer. COMMAND: A FUNCTION: Append lines The A command allows the user to enter a group of lines after the indicated line. Lines are entered until the user types a line containing a single dot (".") in the first column followed by a RETURN. The Insert command is like the Append command except that it inserts lines BEFORE the indicated line, where Append appends lines AFTER the indicated line. COMMAND: D FUNCTION: Delete lines The D command deletes all lines over the indicated range of lines. There is no recovery from this command. COMMAND: F FUNCTION: Find the first occurance of a string The F command searches for the indicated string over the indicated range of lines. The first line in the range which contains the string is positioned to and the line is printed. COMMAND: G FUNCTION: Get a File The G command loads the indicated file into the editor buffer after the indicated line. This command can be used to read in a file to be included in the edit buffer for paste operations, where the Put command is the complementary cut operation. COMMAND: H FUNCTION: Print Help Summary The H command prints a summary of the ALED commands to the user. 7 ALED - A Line-Oriented File Editor Written in Ada COMMAND: I FUNCTION: Insert lines The I command allows the user to enter a group of lines before the indicated line. Lines are entered until the user types a line containing a single dot (".") in the first column followed by a RETURN. The Append command is like the Insert command except that it appends lines AFTER the indicated line, where Insert inserts lines BEFORE the indicated line. COMMAND: J FUNCTION: Jump to the indicated line The J command positions the user at the indicated line. The line is not printed. COMMAND: L FUNCTION: List lines over a range The L command lists all lines over the indicated range of lines. COMMAND: N FUNCTION: Find Next occurance of indicated string The N command searches for the indicated string starting at the next line in the file and proceeding to the end of the file. If the user inputs a blank line (a space followed by a RETURN), the last string referenced by an F or N command is searched for again. COMMAND: P FUNCTION: Put a range of lines into a file The P command writes a group of lines from the edit buffer out to a file on disk. This may be used to create desired external files or it may be used to cut a section out of the edit buffer and paste it in (via the Get command) elsewhere. COMMAND: Q FUNCTION: Quit editor and do not update file The Q command allows the user to exit the editor without changing the original file on the disk. COMMAND: S FUNCTION: Substitute strings The S command substitutes one string for another over the indicated range of lines. All occurrances of the old string are replaced by the new string over this range. COMMAND: X FUNCTION: Exit the editor and update the file The X command exits the editor and updates the file on the disk. 8 ALED - A Line-Oriented File Editor Written in Ada 2.3. SAMPLE SESSION The following is a sample session which illustrates the operation of ALED. Comments are placed out to the side, prefixed by "<--". ALED - Ada Line Editor by Richard Conn, Version 1.0 File Name? t.txt <-- File name is selected New File <-- File does not already exist 0 Lines in File Type H for Help 0> help <-- Help Command --- Movement Commands --- ----- Enter Lines ----- + Advance N Lines A Append after <line> - Back Up N Lines I Insert before <line> F Find <string> in <range> J Jump to <line> ----- Print Lines ----- N Find Next <string> . Print Current Line ----- Delete Command ----- < Print Next Line D Delete lines in <range> > Print Next Line L List over <range> ---- Help and Exits ---- H This Help Text ---- Substitution ---- Q Quit without Updating S String Substitute X Exit and Update over <range> ---- File Get/Put ---- -- Miscellaneous -- G Get <file> after <line> ? Print Statistics P Put <file> over <range> <Range>: % %,% First or Second Entries -- #-Number, .-Current, C-Current, F-First, L-Last Singular Entries -- A-All, P-Page 0> append after <line> . <-- Append Lines into buffer Enter Lines (.<RETURN> to Stop) 1: This is a test and demonstration of ALED 2: This is a very short test, but all commands 3: should be exercised by it 4: Note that all commands are single characters; 5: the editor fills in the prompt with each 6: single character input at the command prompt "n>" 7: A single dot in a line terminates input 8: . <-- Input is complete 9 ALED - A Line-Oriented File Editor Written in Ada 7> list lines in <range> all <-- List all lines 1: This is a test and demonstration of ALED 2: This is a very short test, but all commands 3: should be exercised by it 4: Note that all commands are single characters; 5: the editor fills in the prompt with each 6: single character input at the command prompt "n>" 7: A single dot in a line terminates input 7> list lines in <range> 1,4 <-- List range of lines 1: This is a test and demonstration of ALED 2: This is a very short test, but all commands 3: should be exercised by it 4: Note that all commands are single characters; 4> list lines in <range> -1,+2 <-- List range of lines 3: should be exercised by it 4: Note that all commands are single characters; 5: the editor fills in the prompt with each 6: single character input at the command prompt "n>" 6> list lines in <range> 1 <-- List first line 1: This is a test and demonstration of ALED 1> list lines in <range> p <-- List current page 1: This is a test and demonstration of ALED 2: This is a very short test, but all commands 3: should be exercised by it 4: Note that all commands are single characters; 5: the editor fills in the prompt with each 6: single character input at the command prompt "n>" 7: A single dot in a line terminates input 7> list lines in <range> a <-- List all lines 1: This is a test and demonstration of ALED 2: This is a very short test, but all commands 3: should be exercised by it 4: Note that all commands are single characters; 5: the editor fills in the prompt with each 6: single character input at the command prompt "n>" 7: A single dot in a line terminates input 7> y - Error <-- Invalid Commands 7> _ - Error 7> - back up N lines <line count> 3 <-- Backup 3 lines 4> . <-- Print current line 4: Note that all commands are single characters; 4> + advance N lines <line count> 1 <-- Advance 1 line 5> . <-- Print current line 5: the editor fills in the prompt with each 10 ALED - A Line-Oriented File Editor Written in Ada 5> substitute for old <string> test <-- substitute new <string> xx over <range> a 1: This is a xx and demonstration of ALED <-- affected 2: This is a very short xx, but all commands <-- lines 7> substitute for old <string> xx <-- change back new <string> test over <range> 2 2: This is a very short test, but all commands 3> find <string> xx <-- look for "xx" over <range> a 1: This is a xx and demonstration of ALED 1> substitute for old <string> xx <-- change it new <string> test over <range> . 1: This is a test and demonstration of ALED 2> find <string> test <-- look for first over <range> a 1: This is a test and demonstration of ALED 1> next Occurrance of <string> <-- look for next 2: This is a very short test, but all commands 2> list lines in <range> L <-- look at last line 7: A single dot in a line terminates input 7> append after <line> L <-- append lines Enter Lines (.<RETURN> to Stop) 8: This is yet another test 9: These lines are being appended to the 10: end of the file. 11: I am inserting several instances of 12: the word test 13: so that there will be something to search for 14: in further tests of the Next Occurrance command 15: . <-- end input 14> find <string> test <-- search for "test" over <range> a 1: This is a test and demonstration of ALED 1> next Occurrance of <string> <-- search again 2: This is a very short test, but all commands 2> next Occurrance of <string> <-- and again 8: This is yet another test 8> next Occurrance of <string> <-- and again 12: the word test 11 ALED - A Line-Oriented File Editor Written in Ada 12> next Occurrance of <string> <-- and again 14: in further tests of the Next Occurrance command 14> next Occurrance of <string> <-- and again 14: in further tests of the Next Occurrance command 14> substitute for old <string> test <-- change string new <string> xxxxxxx over <range> a 1: This is a xxxxxxx and demonstration of ALED 2: This is a very short xxxxxxx, but all commands 8: This is yet another xxxxxxx 12: the word xxxxxxx 14: in further xxxxxxxs of the Next Occurrance command 14> substitute for old <string> xxxxxxx <-- change back new <string> test over <range> a 1: This is a test and demonstration of ALED 2: This is a very short test, but all commands 8: This is yet another test 12: the word test 14: in further tests of the Next Occurrance command 14> substitute for old <string> test new <string> "test" over <range> 12 12: the word "test" 13> jump to <line> 1 <-- Jump command 1> jump to <line> L <-- Jump to last line 14> jump to <line> 1 <-- Jump to first line 1> list lines in <range> p 1: This is a test and demonstration of ALED 2: This is a very short test, but all commands 3: should be exercised by it 4: Note that all commands are single characters; 5: the editor fills in the prompt with each 6: single character input at the command prompt "n>" 7: A single dot in a line terminates input 8: This is yet another test 9: These lines are being appended to the 10: end of the file. 11: I am inserting several instances of 12: the word "test" 13: so that there will be something to search for 14: in further tests of the Next Occurrance command 14> put <file> q.txt <-- Write lines out over <range> 11,L <-- Limit range 14> get <file> q.txt <-- Read back in after line 1 after <line> 1 12 ALED - A Line-Oriented File Editor Written in Ada 1> list lines in <range> a <-- look at results 1: This is a test and demonstration of ALED 2: I am inserting several instances of 3: the word "test" 4: so that there will be something to search for 5: in further tests of the Next Occurrance command 6: This is a very short test, but all commands 7: should be exercised by it 8: Note that all commands are single characters; 9: the editor fills in the prompt with each 10: single character input at the command prompt "n>" 11: A single dot in a line terminates input 12: This is yet another test 13: These lines are being appended to the 14: end of the file. 15: I am inserting several instances of 16: the word "test" 17: so that there will be something to search for 18: in further tests of the Next Occurrance command 18> get <file> q.txt <-- read lines back in after <line> 7 7> list lines in <range> p <-- list page of lines 7: should be exercised by it 8: I am inserting several instances of 9: the word "test" 10: so that there will be something to search for 11: in further tests of the Next Occurrance command 12: Note that all commands are single characters; 13: the editor fills in the prompt with each 14: single character input at the command prompt "n>" 15: A single dot in a line terminates input 16: This is yet another test 17: These lines are being appended to the 18: end of the file. 19: I am inserting several instances of 20: the word "test" 21: so that there will be something to search for 22: in further tests of the Next Occurrance command 22> insert before <line> 16 <-- insert line Enter Lines (.<RETURN> to Stop) 16: testtesttesttest 17: . <-- end input 17> < <-- backup 16: testtesttesttest 16> < 15: A single dot in a line terminates input 15> > 16: testtesttesttest 13 ALED - A Line-Oriented File Editor Written in Ada 16> > 17: This is yet another test 17> < 16: testtesttesttest 16> . 16: testtesttesttest 16> substitute for old <string> test <-- substitute new <string> xxxx over <range> . 16: xxxxtesttesttest <-- observe progress of 16: xxxxxxxxtesttest <-- substitute command 16: xxxxxxxxxxxxtest 16: xxxxxxxxxxxxxxxx 17> < 16: xxxxxxxxxxxxxxxx 16> substitute for old <string> xxxx <-- and again new <string> test over <range> . 16: testxxxxxxxxxxxx 16: testtestxxxxxxxx 16: testtesttestxxxx 16: testtesttesttest 17> jump to <line> 1 1> ? <-- statistics Edit File Name: t.txt 23 Lines in File 1> jump to <line> L <-- verify line count 23> jump to <line> 1 1> list lines in <range> . 1: This is a test and demonstration of ALED 1> . 1: This is a test and demonstration of ALED 14 ALED - A Line-Oriented File Editor Written in Ada 1> list lines in <range> p 1: This is a test and demonstration of ALED 2: I am inserting several instances of 3: the word "test" 4: so that there will be something to search for 5: in further tests of the Next Occurrance command 6: This is a very short test, but all commands 7: should be exercised by it 8: I am inserting several instances of 9: the word "test" 10: so that there will be something to search for 11: in further tests of the Next Occurrance command 12: Note that all commands are single characters; 13: the editor fills in the prompt with each 14: single character input at the command prompt "n>" 15: A single dot in a line terminates input 16: testtesttesttest 17: This is yet another test 18: These lines are being appended to the 19: end of the file. 20: I am inserting several instances of 21: the word "test" 21> delete lines in <range> 8,11 <-- delete lines 8> jump to <line> 1 1> list lines in <range> p 1: This is a test and demonstration of ALED 2: I am inserting several instances of 3: the word "test" 4: so that there will be something to search for 5: in further tests of the Next Occurrance command 6: This is a very short test, but all commands 7: should be exercised by it 8: Note that all commands are single characters; 9: the editor fills in the prompt with each 10: single character input at the command prompt "n>" 11: A single dot in a line terminates input 12: testtesttesttest 13: This is yet another test 14: These lines are being appended to the 15: end of the file. 16: I am inserting several instances of 17: the word "test" 18: so that there will be something to search for 19: in further tests of the Next Occurrance command 19> delete lines in <range> 2,5 <-- delete more lines 15 ALED - A Line-Oriented File Editor Written in Ada 2> list lines in <range> a 1: This is a test and demonstration of ALED 2: This is a very short test, but all commands 3: should be exercised by it 4: Note that all commands are single characters; 5: the editor fills in the prompt with each 6: single character input at the command prompt "n>" 7: A single dot in a line terminates input 8: testtesttesttest 9: This is yet another test 10: These lines are being appended to the 11: end of the file. 12: I am inserting several instances of 13: the word "test" 14: so that there will be something to search for 15: in further tests of the Next Occurrance command 15> Exit and update file (Y/N)? n 15> quit without File Update (Y/N)? n 15> Exit and update file (Y/N)? y -) type t.txt <-- final file This is a test and demonstration of ALED This is a very short test, but all commands should be exercised by it Note that all commands are single characters; the editor fills in the prompt with each single character input at the command prompt "n>" A single dot in a line terminates input testtesttesttest This is yet another test These lines are being appended to the end of the file. I am inserting several instances of the word "test" so that there will be something to search for in further tests of the Next Occurrance command -) type q.txt <-- Q.TXT file I am inserting several instances of the word "test" so that there will be something to search for in further tests of the Next Occurrance command -) del q.txt -) x editor ALED - Ada Line Editor by Richard Conn, Version 1.0 File Name? t.txt <-- reedit file 15 Lines in File Type H for Help 16 ALED - A Line-Oriented File Editor Written in Ada 1> list lines in <range> a 1: This is a test and demonstration of ALED 2: This is a very short test, but all commands 3: should be exercised by it 4: Note that all commands are single characters; 5: the editor fills in the prompt with each 6: single character input at the command prompt "n>" 7: A single dot in a line terminates input 8: testtesttesttest 9: This is yet another test 10: These lines are being appended to the 11: end of the file. 12: I am inserting several instances of 13: the word "test" 14: so that there will be something to search for 15: in further tests of the Next Occurrance command 15> delete lines in <range> 8 8> quit without File Update (Y/N)? y <-- demo QUIT -) x editor ALED - Ada Line Editor by Richard Conn, Version 1.0 File Name? t.txt <-- reedit file 15 Lines in File Type H for Help 1> list lines in <range> a 1: This is a test and demonstration of ALED 2: This is a very short test, but all commands 3: should be exercised by it 4: Note that all commands are single characters; 5: the editor fills in the prompt with each 6: single character input at the command prompt "n>" 7: A single dot in a line terminates input 8: testtesttesttest 9: This is yet another test 10: These lines are being appended to the 11: end of the file. 12: I am inserting several instances of 13: the word "test" 14: so that there will be something to search for 15: in further tests of the Next Occurrance command 15> delete lines in <range> 8 <-- remove line from file 8> Exit and update file (Y/N)? y <-- demo EXIT 17 ALED - A Line-Oriented File Editor Written in Ada -) type t.txt <-- show result This is a test and demonstration of ALED This is a very short test, but all commands should be exercised by it Note that all commands are single characters; the editor fills in the prompt with each single character input at the command prompt "n>" A single dot in a line terminates input This is yet another test These lines are being appended to the end of the file. I am inserting several instances of the word "test" so that there will be something to search for in further tests of the Next Occurrance command 18 ALED - A Line-Oriented File Editor Written in Ada 3. S Y N O P S I S a n d C O M M E N T S In summary, the following items were learned from this experience: 1. Ada is feasible; the editor ran with reasonable speed 2. The Ada code was fairly efficient; EDITOR used only TEXT_IO for support, and, after a 58K initial overhead, the growth of code was approximately 9 words/line of code 3. Standardization under TEXT_IO needs some work; some simple, fundamental items, such as an input line editor available under GET_LINE, are missing (this is why I had to write my own input line editor) and GET does not return or pass every possible character (the DEL character does not pass thru the GET routine in my TEXT_IO package, for instance); do all GET routines allow single-character input? 4. Generics are useful and work well; software components libraries will be quite beneficial in reducing programming overhead once they have been developed 5. Exceptions are very, very useful; note their use throughout the code and how they are fundamental to the design (note the BEGIN/END in the main loop) 6. Ada code can be written to be quite readable and maintainable; I feel that I have successfully done this with ALED (assuming that knowledge of the generic package in LIST.ADA is known) 19 ALED - A Line-Oriented File Editor Written in Ada I n d e x + + Command, 7 - - Command, 7 < < Command, 6 > > Command, 6 ? ? Command, 7 A A Command, 7 Aborting Commands, 6 Ada, 1 Advance Line, 6 Advance N Lines, 7 Advanced Development Model, 1 ALED Aborting Commands, 6 ADM, 1 Advanced Development Model, 1 EDM, 1 Engineering Development Model, 1 Help Command, 3 Input Line Editor, 6 Line Input, 5 Line Ranges, 4 Line References, 5 Prompt, 2 Purpose, 1 String Input, 5 Append Lines, 7 B Back Up Line, 6 Back Up N Lines, 7 C Command +, 7 -, 7 ., 6 <, 6 >, 6 ?, 7 A, 7 D, 7 F, 7 20 ALED - A Line-Oriented File Editor Written in Ada G, 7 H, 7 I, 8 J, 8 L, 8 N, 8 P, 8 Q, 8 S, 8 X, 8 COMMANDS, 6 D D Command, 7 Delete Lines, 7 Dot Command, 6 E Engineering Development Model, 1 Exit, 8 F F Command, 7 File Get, 7 Put, 8 Find Next String, 8 Find String, 7 G G Command, 7 Get File, 7 H H Command, 7 Help, 3, 7 I I Command, 8 Input Line Editor, 6 Insert Lines, 8 INTRODUCTION, 1 J J Command, 8 Jump to Line, 8 L L Command, 8 Line Range Specification, 4 Line Reference Specification, 5 List Lines, 8 21 ALED - A Line-Oriented File Editor Written in Ada N N Command, 8 Next String, 8 P P Command, 8 PRELIMINARIES, 4 Print Current Line, 6 Print Statistics, 7 Put File, 8 Q Q Command, 8 Quit, 8 S S Command, 8 SAMPLE SESSION, 9 Substitute Strings, 8 SYNOPSIS and COMMENTS, 19 U USING ALED, 2 X X Command, 8 22