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language:controlflow [2019/04/18 14:22]
rajit
language:controlflow [2022/05/13 08:45]
rajit
Line 11: Line 11:
 An example of the loop construct in ACT is shown below: An example of the loop construct in ACT is shown below:
  
-<code>+<code act>
 ( i : 10 : bool x[i..i]; ) ( i : 10 : bool x[i..i]; )
 </code> </code>
Line 20: Line 20:
 range ''0..9''. The body of the loop is the statement ''bool x[i..i];''. The effect of this statement is the same as range ''0..9''. The body of the loop is the statement ''bool x[i..i];''. The effect of this statement is the same as
  
-<code>+<code act>
 bool x[0..0]; bool x[0..0];
 bool x[1..1]; bool x[1..1];
Line 31: Line 31:
 is shown below: is shown below:
  
-<code>+<code act>
 register r[1..8]; register r[1..8];
 (i : 1..8 : r[i](in[i],out[i],control); ) (i : 1..8 : r[i](in[i],out[i],control); )
Line 48: Line 48:
 command language. command language.
  
-<code>+<code act>
 pint i; pint i;
 i=0; i=0;
Line 65: Line 65:
  
 In production rule bodies, the loop In production rule bodies, the loop
-<code>+<code act>
 (&i:3: x[i]) (&i:3: x[i])
 </code> </code>
 expands to expands to
-<code>+<code act>
 x[0] & x[1] & x[2] x[0] & x[1] & x[2]
 </code> </code>
Line 78: Line 78:
  
 ===== Selections ===== ===== Selections =====
 +
 +Conditional execution is supported by the selection statement. The
 +syntax of a selection statement is:
 +
 +<code act>
 +[ boolean_expression -> body 
 +[] boolean_expression -> body
 +..
 +]
 +</code>
 +The last Boolean expression in the conditional can be the keyword
 +''else'', which is short-hand for 'all other guards are false.'
 +
 +Any one body whose corresponding Boolean expression is true is
 +executed. For instance, we can create 32 registers with
 +something special for register 0 as follows:
 +
 +<code act>
 +(i : 32 : 
 +    [ i = 0 -> r0(in[i],out[i],control);
 +   [] else -> r[i](in[i],out[i],control);
 +    ]
 +)
 +</code>
 +
 +Boolean expressions can be constructed from Boolean variables, the
 +constants ''true'' and ''false'', and the Boolean operators
 +''&'', ''|'', and ''~'' denoting the and, or, and negation
 +operations respectively.  Numeric expressions can be compared using
 +''<'', ''< ='', ''>'', ''>='', ''='', and ''!='' for
 +the operators less than, less than or equal to, greater than, greater
 +than or equal to, equal to, and not equal to respectively.
 +
 +===== Recursion =====
 +
 +Type definitions can be recursive. For instance, the following
 +definition can be used to create a tree structure.
 +
 +<code act>
 +template<pint N>
 +defproc tree (bool a[N])
 +{
 +  [ N = 1 -> leaf l(a[0]);
 + [] N > 1 -> tree<N/2> t0(a[0..N/2-1]);
 +             tree<N-N/2> t1(a[N/2..N-1]);
 +  ]
 +}
 +</code>
 +