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AAAA LLLLiiiittttttttlllleeee SSSSmmmmaaaallllllllttttaaaallllkkkk UUUUsssseeeerrrr MMMMaaaannnnuuuuaaaallll Timothy A. Budd _1. _I_n_t_r_o_d_u_c_t_i_o_n This manual is intended as an aid in using the Little Smalltalk system. It is not intended to be used as an introduction to the Smalltalk language. Little Smalltalk is largely (with exceptions listed in a later section) a subset of the Smalltalk-80* language described in [.Smalltalk blue.]. A complete description of the classes included in the Little Smalltalk system and the messages they accept is given in Appendix 1. _2. _R_u_n_n_i_n_g _t_h_e _s_y_s_t_e_m The Little Smalltalk system is invoked by typing the command sssstttt. The system is interactive - that is, the user types an expression at the keyboard and the system responds by evaluating the expression and typing the result. For example, typing the expression 3333 ++++ 4444 results in the value 7777 being displayed on the output. Execution is terminated by typing control-D. A sample execution session is shown in Figure 1. % st Little Smalltalk 3 + 4 7 ^D % FFFFiiiigggguuuurrrreeee 1111:::: A Sample Little Smalltalk Session Instance variables for the command level can be created by assigning a value to a new variable name. Thereafter that variable can be used at the command level, although it is not known within the scope of any method. The variable _________________________ * Smalltalk-80 is a trademark of the Xerox Corporation. September 19, 1986 - 2 - ``last'' always contains the value returned by the last expression typed. Figure 2 shows the creation of a vari- able. Note that the assignment arrow is formed as a two character sequence. newvar <- 2 / 3 newvar 0.666667 2 raisedTo: newvar + (4 / 3) 4 last 4 FFFFiiiigggguuuurrrreeee 2222:::: Creating Variables The default behavior is for the value of expressions, with the exception of assignments, to be typed automatically as they are evaluated. This behavior can be modified either by using the -d flag (see Appendix 2), or by passing a mes- sage to the pseudo variable ssssmmmmaaaallllllllttttaaaallllkkkk (see Appendix 1). Class descriptions must be read in from files, they cannot be entered interactively. Class descriptions are entered using a system directive. For example, to include a class description contained in a file named nnnneeeewwwwccccllllaaaassssssss....sssstttt, the following system directive should be issued: )i newclass.st A list of files containing class descriptions can also be given as arguments to the st command. The command %st file1 ... filen is equivalent to the sequence %st Little Smalltalk )i file1 ... )i filen A table of system directives is given in Figure 3. Note that the )e system directive invokes an editor on a file containing class descriptions, and then automatically includes the file when the editor is exited. Classes also respond to the message eeeeddddiiiitttt, which will have the same effect as the )e directive applied to the file containing the class description. Thus the typical debug/edit/debug cycle September 19, 1986 - 3 - _____________________________________________________________ )e filename Edit the named file. The Little Smalltalk system will suspend, leaving the user in an editor for making changes to the named file. Upon leaving the editor the named file will automatically be included, as if the )i directive had been typed. )g filename Search for an entry in the system library area matching the filename. If found, the class descriptions in the library entry are included. This command is useful for including commonly used classes that are not part of the standard prelude, such as classes for statistics applications or graphics. )i filename Include the named file. The file must contain one or more class descriptions. The class descriptions are parsed, and if syntactically legal new instances of class CCCCllllaaaassssssss are added to the Smalltalk system. )l filename Load a previously saved environment from the named file. The current values of all variables are overridden. The file must have been created using the )s directive (below). )r filename Read the named file. The file must contain Smalltalk statements, as would be typed at the keyboard. The effect is just as if the lines of the file had been typed at the keyboard. The file cannot contain class descriptions. )s filename Save the current state in the named file. The values of all variables are saved, and can later be reloaded using the )l directive (above). )!string Execute the remainder of the line following the exclamation point as a Unix* command. Nothing is done with the output of the command, nor is the returning status of the command recorded. _____________________________________________________________ |||||||||||||||||||||||||||||||||||||||||||||| |||||||||||||||||||||||||||||||||||||||||||||| FFFFiiiigggguuuurrrreeee 3333:::: System Directives September 19, 1986 - 4 - involves repeated uses of the )e directive or the eeeeddddiiiitttt mes- sage until a desired outcome is achieved. The editor invoked by the )e directive can be changed by setting the EDITOR variable in the users environment. _3. _D_i_f_f_e_r_e_n_c_e_s _b_e_t_w_e_e_n _L_i_t_t_l_e _S_m_a_l_l_t_a_l_k _a_n_d _t_h_e _S_m_a_l_l_t_a_l_k- _8_0 _s_y_s_t_e_m This section describes the differences between the language accepted by the Little Smalltalk system and the language described in [.Smalltalk blue.]. The principal reasons for these changes are as follows: size Classes which are largely unnecessary, or which could be easily simulated by other classes (e.g. Associa- tion, SortedCollection) have been eliminated in the interest of keeping the size of the standard library as small as possible. Similarly, indexed instance variables are not supported, since to do so would increase the size of every object in the system, and they can be easily simulated in those classes in which they are important (see below). portability Classes which depend upon particular hardware (e.g. BitBlt) are not included as part of the Little Smalltalk system. The basic system assumes nothing more than ascii terminals. representation The need for a textual representation for class descriptions required some small additions to the syn- tax for class methods (see Appendix 3). Similarly, the fact that classes and subclasses can be separately parsed, in either order, forced some changes in the scoping rules for instance variables. The following sections describe these changes in more detail. _3._1. _N_o _B_r_o_w_s_e_r The Smalltalk-80 Programming Environment described in [.Smalltalk orange.] is not included as part of the Little Smalltalk system. The Little Smalltalk system is designed to be little, easily portable, and to rely on nothing more than basic terminal capabilities. _3._2. _I_n_t_e_r_n_a_l _R_e_p_r_e_s_e_n_t_a_t_i_o_n _D_i_f_f_e_r_e_n_t The internal representations of objects, including processes, interpreters, and bytecodes, is entirely dif- ferent in the Little Smalltalk system from the Smalltalk-80 system described in [.Smalltalk blue.]. _________________________ * Unix is a trademark of Bell Laboratories. September 19, 1986 - 5 - _3._3. _F_e_w_e_r _C_l_a_s_s_e_s Many of the classes described in [.Smalltalk blue.] are not included as part of the Little Smalltalk basic system. Some of these are not necessary because of the decision not to include the editor, browser, and so on as part of the basic system. Others are omitted in the interest of keeping the standard library of classes small. A complete list of included classes for the Little Smalltalk system is given in Appendix 1. _3._4. _N_o _C_l_a_s_s _P_r_o_t_o_c_o_l Protocol for all classes is defined as part of class CCCCllllaaaassssssss. It is not possible to redefine class protocol as part of a class description, only instance protocol. The notion of metaclasses is not supported. _3._5. _C_a_s_c_a_d_e_s _D_i_f_f_e_r_e_n_t The semantics of cascades has been simplified and gen- eralized. The result of a cascaded expression is always the result of the expression to the left of the first semicolon, which is also the receiver for each subsequent continuation. Continuations can include multiple messages. A rather non- sensical, but illustrative, example is the following: 2 + 3 ; - 7 + 3 ; * 4 The result of this expression is 5 (the value yielded by 2 + 3). 5 is also the receiver for the message - 7, and that result (-2) is in turn the receiver for the message + 3. This last result is thrown away. 5 is then again used as the receiver for the message * 4, the result of which is also thrown away. _3._6. _I_n_s_t_a_n_c_e _V_a_r_i_a_b_l_e _N_a_m_e _S_c_o_p_e In the language described in [.Smalltalk blue.], an instance variable is known not only to the class protocol in which it is declared, but is also valid in methods defined for any subclasses of that class. In the Little Smalltalk system an instance variable can be referenced only within the protocol for the class in which it is declared. _3._7. _I_n_d_e_x_e_d _I_n_s_t_a_n_c_e _V_a_r_i_a_b_l_e_s Implicitly defined indexed instance variables are not supported. In any class for which these are desired they can be easily simulated by including an additional instance variable, containing an Array, and including the following methods: September 19, 1986 - 6 - Class Whatever | indexVars | [ new: size indexVars <- Array new: size | at: location |^ indexVars at: location | at: location put: value indexVars at: location put: value ... The message new: can be used with any class, with an effect similar to new. That is, if a new instance of the class is created by sending the message new: to the class variable, the message is immediately passed on to the new instance, and the result returned is used as the result of the creation message. _3._8. _N_o _P_o_o_l _V_a_r_i_a_b_l_e_s The concepts of pool variables, global variables, or class variables are not supported. In their place there is a new pseudo-variable, ssssmmmmaaaallllllllttttaaaallllkkkk, which responds to the mes- sages aaaatttt:::: and aaaatttt::::ppppuuuutttt::::. The keys for this collection can be arbitrary. Although this facility is available, its use is often a sign of poor program design, and should be avoided. _3._9. _N_o _A_s_s_o_c_i_a_t_i_o_n_s The class Dictionary stores keys and values separately, rather than as instances of Association. The class Associa- tion, and all messages referring to Associations have been removed. _3._1_0. _G_e_n_e_r_a_t_o_r_s _i_n _p_l_a_c_e _o_f _S_t_r_e_a_m_s The notion of stream has been replaced by the slightly different notion of _g_e_n_e_r_a_t_o_r_s, in particular the use of the messages _f_i_r_s_t and _n_e_x_t in subclasses of CCCCoooolllllllleeeeccccttttiiiioooonnnn. Exter- nal files are supported by an explicit class FFFFiiiilllleeee. _3._1_1. _P_r_i_m_i_t_i_v_e_s _D_i_f_f_e_r_e_n_t Both the syntax and the use of primitives has been changed. Primitives provide an interface between the Smalltalk world and the underlying system, permitting the execution of operations that cannot be specified in Smalltalk. In Little Smalltalk, primitives cannot fail and September 19, 1986 - 7 - must return a value (although they may, in error situations, print an error message and return nnnniiiillll). The syntax for primitives has been altered to permit the specification of primitives with an arbitrary number of arguments. The for- mat for a primitive call is as follows: <primitive nnnnuuuummmmbbbbeeeerrrr _a_r_g_u_m_e_n_t_l_i_s_t > Where nnnnuuuummmmbbbbeeeerrrr is the number of the primitive to be executed (which must be a value between 1 and 255), and _a_r_g_u_m_e_n_t_l_i_s_t is a list of Smalltalk primary expressions (see Appendix 2). Appendix 4 lists the meanings of each of the currently recognized primitive numbers. _3._1_2. _B_y_t_e _A_r_r_a_y_s A new syntax has been created for defining an array composed entirely of unsigned integers in the range 0-255. These arrays are given a very tight encoding. The syntax is a pound sign, followed by a left square brace, followed by a sequence of numbers in the range 0 to 255, followed by a right square brace. #[ _n_u_m_b_e_r_s ] Byte Arrays are used extensively internally. _3._1_3. _N_e_w _P_s_e_u_d_o _V_a_r_i_a_b_l_e_s In addition to the pseudo variable ssssmmmmaaaallllllllttttaaaallllkkkk already mentioned, another pseudo variable, sssseeeellllffffPPPPrrrroooocccceeeessssssss, has beed added to the Little Smalltalk system. sssseeeellllffffPPPPrrrroooocccceeeessssssss returns the currently executing process, which can then be passed as an argument to a semaphore, or be used as a receiver for a message valid for class PPPPrrrroooocccceeeessssssss. Like sssseeeellllffff and ssssuuuuppppeeeerrrr, sssseeeellllffffPPPPrrrroooocccceeeessssssss cannot be used at the command level. _3._1_4. _N_o _D_e_p_e_n_d_e_n_c_y The notion of dependency, and automatic dependency updating, is not included in Little Smalltalk. September 19, 1986 _A_p_p_e_n_d_i_x _1 _C_l_a_s_s _D_e_s_c_r_i_p_t_i_o_n_s The messages accepted by the classes included in the Little Smalltalk standard library are described in the fol- lowing pages. A list of the classes defined, where indenta- tion is used to imply subclassing, is given below: Object UndefinedObject Symbol Boolean True False Magnitude Char Number Integer Float Radian Point Random Collection Bag Set KeyedCollection Dictionary Smalltalk File SequenceableCollection Interval LinkedList Semaphore File ArrayedCollection Array ByteArray String Block Class Process In the descriptions of each message the following notes may occur: _d Indicates the effect of the message differs slightly from that given in [.Smalltalk blue.]. _n Indicates the message is not included as part of the language defined in [.Smalltalk blue.]. _r Indicates the protocol for the message overrides a pro- tocol given in some superclass. Only where the logical September 19, 1986 effect of this overriding is important is the message given a second time; some messages, such as copy, are overridden in many classes but are not described in the documentation because the logical effect remains the same. September 19, 1986 _A_p_p_e_n_d_i_x _2 _M_a_n _P_a_g_e A Unix man page for the st command is given on the fol- lowing page. September 19, 1986 _A_p_p_e_n_d_i_x _3 _S_y_n_t_a_x _C_h_a_r_t_s Syntax charts for the language accepted by the Little Smalltalk system are described on the following pages. The following is an example class description: Class Set :Collection | dict | [ new dict <- Dictionary new | add: newElement dict at: newElement ifAbsent: [dict at: newElement put: 1] | remove: oldElement ifAbsent: exceptionBlock dict removeKey: oldElement ifAbsent: exceptionBlock | size |^ dict size | occurrencesOf: anElement |^ dict at: anElement ifAbsent: [0] | first dict first. |^ dict currentKey | next dict next. |^ dict currentKey ] September 19, 1986 _A_p_p_e_n_d_i_x _4 _P_r_i_m_i_t_i_v_e _N_u_m_b_e_r_s The following chart gives the function performed by each primitive in the Little Smalltalk system. _I_n_f_o_r_m_a_t_i_o_n _a_b_o_u_t _o_b_j_e_c_t_s 0 (not used ) 1 class of an object 2 superobject of an object 3 test if class responds to new 4 size of object 5 hash value 6 test if two built-in objects are of the same type 7 object equality testing ( == ) 8 various switch toggles 9 numerical generality testing _I_n_t_e_g_e_r _m_a_n_i_p_u_l_a_t_i_o_n 10 integer addition (both args must be integer) 11 integer subtraction 12 integer < test 13 integer > test 14 integer <_ test 15 integer >_ test 16 integer = test 17 integer ~= test 18 integer multiplication 19 integer // _B_i_t _m_a_n_i_p_u_l_a_t_i_o_n _a_n_d _o_t_h_e_r _i_n_t_e_g_e_r _v_a_l_u_e_d _f_u_n_c_t_i_o_n_s 20 gcd: September 19, 1986 21 bitAt: 22 bitOr: 23 bitAnd: 24 bitXor: 25 bitShift: 26 radix: 27 not used 28 integer quo: 29 integer rem: _O_t_h_e_r _i_n_t_e_g_e_r _f_u_n_c_t_i_o_n_s 30 doPrimitive:withArguments: 31 not used 32 convert random integer to random float 33 bitInvert 34 highBit 35 randomNumber (argument is seed ) 36 asCharacter 37 asString 38 factorial 39 asFloat _C_h_a_r_a_c_t_e_r _m_a_n_i_p_u_l_a_t_i_o_n 40 not used 41. not used 42 character < test 43 character > test 44 character <_ test 45 character >_ test September 19, 1986 46 character = test 47 character ~= test 48 not used 49 not used _C_h_a_r_a_c_t_e_r _u_n_a_r_y _f_u_n_c_t_i_o_n_s 50 digitValue 51 isVowel 52 isLetter 53 isLowerCase 54 isUpperCase 55 isSeparator 56 isAlphaNumeric 57 caseShift 58 asString 59 asciiValue _F_l_o_a_t_i_n_g _p_o_i_n_t _m_a_n_i_p_u_l_a_t_i_o_n 60 floating point addition (both args must be float) 61 floating point subtraction 62 floating point < test 63 floating point > test 64 floating point <_ test 65 floating point >_ test 66 floating point = test 67 floating point ~= test 68 floating point multiplication 69 floating point division September 19, 1986 _O_t_h_e_r _f_l_o_a_t_i_n_g _p_o_i_n_t _o_p_e_r_a_t_i_o_n_s 70 ln 71 sqrt 72 floor 73 ceiling 74 not used 75 integerPart 76 fractionalPart 77 gamma 78 asString 79 exp _O_t_h_e_r _n_u_m_e_r_i_c_a_l _f_u_n_c_t_i_o_n_s 80 normalize number to be within 0 and 2J. 81 sin 82 cos 83 not used 84 arcSin 85 arcCos 86 arcTan 87 not used 88 raisedTo: 89 radix: _S_y_m_b_o_l _C_o_m_m_a_n_d_s 90. not used 91 symbol comparison, returns true or false. 92 printString 93 asString September 19, 1986 94 print (used internally) 95 not used 96 not used 97 build a new class, arguments are class name, superclass name, instance variables, messages, methods, context size. 98 insert an object into class dictionary, first argument is symbol, second argument is class definition 99 find an object in class dictionary. argument is sym- bol. _S_t_r_i_n_g _o_p_e_r_a_t_i_o_n_s 100 string length 101 string compare, case important - return -1, 0 or 1. 102 string compare, case not important 103 string catenation 104 string at: 105 string at:put: 106 copyFrom:length: 107 copy (new string with same chars) 108 asSymbol 109 string printString _A_r_r_a_y _m_a_n_i_p_u_l_a_t_i_o_n 110 build an untyped object of given size, argument is integer size. 111 index variable get (first argument is object, second is index) 112 index variable put (first argument is object, second is index, third argument is expression) 113 object grow (returns a new object with same instance variable values as first argument, but with second argument tacked on end as new instance variable) 114 build an instance of AAAArrrrrrrraaaayyyy of the given size. September 19, 1986 115 new string of given size 116 ByteArray new: 117 ByteArray size 118 ByteArray at: 119 ByteArray at:put: _O_u_t_p_u_t _a_n_d _e_r_r_o_r _m_e_s_s_a_g_e_s 120 print string with no return 121 print string with return 122 general error - first argument is receiver, second is error string 123 print string on error output (with return) 124 not used 125 unix system call 126 print a string at a specific point on the terminal 127 block return without surrounding context 128 reference count less than zero, first argument is guilty object 129 does not respond error, first argument is receiver, second is message. _F_i_l_e _o_p_e_r_a_t_i_o_n_s 130 file open, first argument is name, second argument is mode 131 file read 132 file write 133 set file mode, first argument is file, second is mode indicator (anInteger) 134 compute file size in bytes 135 file set location (at:) second argument is location (anInteger) 136 return current file offset in bytes September 19, 1986 137 not used 138 not used 139 not used _P_r_o_c_e_s_s _m_a_n_a_g_e_m_e_n_t 140 block execute (trapped by interpreter) 141 new process (withArguments:) 142 terminate a process 143 perform:withArguments: (trapped by interpreter) 144. not used 145 set state 146 return state 148 start atomic action 149 end atomic action _O_p_e_r_a_t_i_o_n_s _o_n _c_l_a_s_s_e_s 150 class edit 151 superclass of a class 152 class name (a Symbol) 153 new instance of a class 154 list all commands class responds to 155 respondsTo: , second argument is a symbol 156 class view (drop into editor, but no include) 157 class list 158 variables (returns an array of symbols) 159 not used _D_a_t_e _a_n_d _T_i_m_e 160 current date and time as string 161 seconds time counter September 19, 1986 162 clear the screen _P_l_o_t(_3) _i_n_t_e_r_f_a_c_e 170 clear the screen 171 move the cursor (move(x,y)) 172 draw a line (cont(x,y)) 173 draw a point (point(x,y)) 174 draw a circle (circle(x,y,r)) 175 draw an arc (arc(x,y,x0,y0,x1,y1)) 176 establish the coordinate space (space(a,b,c,d)) 177 draw a line (line(a,b,c,d)) 178 print a label (label(s)) 179 establish a line type (linemod(s)) September 19, 1986