== CIVL IR ==

=== Language principles ===

* CIVL-IR is a subset of CIVL-C.  A CIVL-IR program is a CIVL-C program, and has the same semantics.

=== Grammar ===

{{{
program: typedef* vardecl* fundef+ ;
block: '{' typedef* vardecl* fundef* statement* '}' ;
statement: block | basicStmt ;
basicStmt:  (ID ':')? (simpleStmt | chooseStmt | gotoStmt) ;
gotoStmt: 'goto' ID ;
simpleStmt: (guardedStmt | primitiveStmt) gotoStmt? ;
guardedStmt: 'when' expr 'do' primitiveStmt ;
chooseStmt: 'begin choose' simpleStmt+ 'end choose' ;
typedef: 'type' ID '=' typeName ';' ;
vardecl: 'var' varopts? ID ':' typeName ';' ;
varopts: '[' varopt+ ']' ;
varopt: 'input' | 'output' ;
fundef:  'fun' funopts? ID '(' paramlist ')' (':' typeName)? conclause* block ;
funopts: '[' funopt+ ']' ;
conclause : 'assigns' expr ';' 
          | 'requires' expr ';'
          | 'ensures' expr ';'
          ...
}}}


=== Types ===
* `$bool` : boolean type ($true and $false, unrelated to integers)
* `$char` : character type (Unicode characters, unrelated to integers)
* `$int` : mathematical integers
* `$real` : mathematical reals
* `$float<e,f>` : IEEE floating-point numbers e=significand bits, f=exponent bits
* `$herbrand<T>` : Herbrand type of non-Herbrand numeric type T
* `$proc` : process type
* `$bundle`: bundle type for sequence of any type (same as seq<T>?)
* `$heap` : heap type, for dynamic allocation
* `$range` : regular sequence of integers
* `$domain` : tuple of ranges
* `$mem` : set of memory locations
* `enum tag` : enumerated type
* `struct tag` : structured type, can also be used for "tuples"
* `union tag` : union type
* `T[]` : array of T
* `void *` : pointer to anything
* `T *` : pointer to T
* `T(T1, ..., Tn)` : function (aka procedure) consuming T1, ..., Tn and returning T
* `$seq<T>` : sequence of T
* `$set<T>` : set of T
* `$map<T1,T2>` : map from T1 to T2
* `$rel<T1, ..., Tn>` : relation,  set of n-tuples

Notes
* Sequences, sets, maps, and relations are immutable.   An assignment using objects of this type creates a new copy of the object, just as with primitive types like `int`.
* The main difference between the array type and the sequence type is that elements of an array are addressable, i.e., one can form a pointer such as `&a[i]`.  This is not possible with sequences, sets, maps, or relations---there is no way to have a pointer to any component of such a type.
* The difference between the function type and map type: a function is really a procedure in the language, so it can modify the state as well as return a value.    This is like the C notion of "function".   A map is a logical partial function: it is defined on some subset of the domain type, it will always "return" the same value on a given input, and reading it cannot modify the state.

Questions
* how to allocate an array
* how to initialize a variable (what are initial values?)
* how to go between sequences and arrays
* can you make types values? (reification)