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6 <TITLE>Compound Statements</TITLE>
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14 <H4><U><I>Loglan 82, A micro-manual of the programming language
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15 - Basic constructs and facilities</I></U></H4>
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17 <H1><IMG ALIGN=MIDDLE SRC="gifs/logo2.gif"> 2) Compound Statements
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22 Compound statements in LOGLAN-82 are built up from simple statements
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23 (like assignment statement e.g. x:=y+0.5, call statement e.g.
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24 call P(7,x+5) etc.) by means of conditional, iteration and case
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27 The syntax of conditional statement is as follows:
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29 <IMG SRC="gifs/cs01.gif">
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31 where "<B>else</B> part" may be omitted:
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33 <IMG SRC="gifs/cs02.gif">
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35 The semantics of conditional statement is standard. The keyword
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36 <B>fi</B> allows to nest conditional statements without appearence
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37 of "dangling <B>else</B>" ambiguity.
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41 <IMG SRC="gifs/cs03.gif">
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43 The statements in a sequence of statements are separated with
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44 semicolons (semicolon may end a sequence , and then, the last
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45 statement in the sequence is the empty statement).
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47 The short circuit control forms are realized in LOGLAN-82 by the
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48 conditional statements with <B>orif</B> (or <B>andif</B>) list.
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49 A conditional statement with <B>orif</B> list has the form:
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51 <IMG SRC="gifs/cs04.gif">
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53 and corresponds somehow to a conditional statement:
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55 <IMG SRC="gifs/cs05.gif">
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57 The above conditional statement (without orif list) selects for
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58 execution one of two sequences of statements, depending on the
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59 truth value of the boolean expression:
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61 <IMG SRC="gifs/cs06.gif">
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63 which is always evaluated till the end. For the execution of the
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64 conditional statement with <B>orif</B> list the specified conditons
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65 wb1,...,wbk are evaluated in succession, until the first one evaluates
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66 to true. Then the rest of the sequence wb1,...,wbk is abandoned
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67 and "<B>then</B> part" is executed. If none of the conditions
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68 wb1,...,wbk evaluates to true "<B>else</B> part" is
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71 Conditional statements with <B>orif</B> list facilitate to program
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72 those conditions, which evaluation to the end may raise a run-time
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77 The execution of the statement:
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79 <IMG SRC="gifs/cs07.gif">
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81 where the value of i is greater than n, and A is an array with
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82 upper bound n, will raise the run-time error. Then the user can
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85 <IMG SRC="gifs/cs08.gif">
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87 what allows to avoid this run-time error and probably agrees with
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90 Conditional statement with andif list has the form:
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92 <IMG SRC="gifs/cs09.gif">
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94 For the execution of this kind of statements, the conditions wb1,...,wbk
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95 are evaluated in succession, until the first one evaluates to
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96 false; then "<B>else</B> part" (if any) is executed.
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97 Otherwise "<B>then</B> part" is executed.
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99 Iteration statement in LOGLAN-82 has the form:
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101 <IMG SRC="gifs/cs10.gif">
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103 An iteration statement specifies repeated execution of the sequence
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104 of statements and terminates with the execution of the simple
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105 statement <B>exit</B>
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109 <IMG SRC="gifs/cs11.gif">
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111 If two iteration statements are nested, then double <B>exit</B>
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112 in the inner one terminates both of them.
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116 <IMG SRC="gifs/cs12.gif">
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118 In the example above simultaneous assignment statements are illustrated
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119 (e.g. r,x:=0) and comments, which begin with a left parenthesis
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120 immediately followed by an asterisk and end with an asterisk immediately
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121 followed by a right parenthesis.
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123 Triple <B>exit</B> terminates three nested iteration statements,
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124 four <B>exit</B> terminates four nested iteration statements etc.
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126 The iteration statement with <B>while</B> condition:
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128 <IMG SRC="gifs/cs13.gif">
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132 <IMG SRC="gifs/cs14.gif">
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134 The iteration statements with controlled variables (for statements)
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137 <IMG SRC="gifs/cs15.gif">
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141 <IMG SRC="gifs/cs16.gif">
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143 The type of the controlled variable j must be discrete. The value
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144 of this variable in the case of the for statement with to is increased,
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145 and in the case of the <B>for</B> statement with <B>downto</B>
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146 is decreased. The discrete range begins with the value of wa1
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147 and changes with the step equal to the value of wa2. The execution
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148 of the <B>for</B> statement with to terminates when the value
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149 of j for the first time becomes greater than the value of wa3
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150 (with downto when the value of j for the first time becomes less
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151 than the value of wa3). After the for statement termination the
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152 value of its controlled variable is determined and equal to the
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153 first value exceeding the specified discrete range.
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155 The values of expressions wa1, wa2 and wa3 are evaluated once,
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156 upon entry to the iteration statement. Default value of wa2 is
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157 equal 1 (when the keyword step and expression wa2 are omitted).
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159 <B>For</B> or <B>while</B> statements may be combined with exit
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164 <IMG SRC="gifs/cs17.gif">
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166 The above iteration statement terminates either for the least
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167 j, 1<=j<=n, such that x=A(j) or for j=n+1 when x=/=A(j),
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170 To enhance the user's comfort, the simple statement <B>repeat</B>
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171 is provided. It may appear in an iteration statement and causes
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172 the current iteration to be finished and the next one to be continued
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173 (something like jump to CONTINUE in Fortran's DO statements).
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177 <IMG SRC="gifs/cs18.gif">
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179 Just as <B>exit</B>, <B>repeat</B> may appear in <B>for</B> statement
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180 or <B>while</B> statement. Then the next iteration begins with
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181 either the evaluation of a new value of the controlled variable
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182 (<B>for</B> statement) or <B>with</B> the evaluation of the condition
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185 Case statement in LOGLAN-82 has the form:
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187 <IMG SRC="gifs/cs19.gif">
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189 where WA is an expression , L1,...,Lk are constants and I1,...,
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190 Ik,I are sequences of statements.
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192 A <B>case</B> statement selects for execution a sequence of statements
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193 Ij, 1<=j<=k, where the value of WA equals Lj. The choice
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194 <B>otherwise</B> covers all values (possibly none) not given in
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195 the previous choices. The execution of a <B>case</B> statement
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196 chooses one and only one alternative (since the choices are to
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197 be exhaustive and mutually exclusive). <HR>
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207 Last update 02/07/95
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211 Comments, suggestions and critiques are welcome to : <A HREF="mailto:linfo062@crisv2.univ-pau.fr">linfo062@crisv2.univ-pau.fr</A>
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