Calder!

Calder has no semicolons. Calder has no statement ordering. Calder uses ! to separate statements, because ! is symmetric, and hence implies commutativity, while ; is not and does not.

programs

Calder programs consist of a single calder expression, which are fairly traditional, except for:

if ... fi

An if/fi expression is composed of multiple statements, separated by !, in any order.

• match expr : describes the subject of the if/fi
• pat -> expr : if pat matches the subject, the value of the if/fi will be the value of expr
• expr <- pat : same as above, mutatis mutandis

(in principle, Calder should check the patterns to provide a most-specific-match-is-taken semantics. in practice, for the current implementation the programmer needs to limit themselves to pairwise disjoint patterns)

val ... lav

A val/lav expression is composed of multiple statements, separated by !, in any order.

• of expr : the value of the val/lav will be the value of expr
• name: expr : name will be bound to expr in any other statements where its value is referenced
• expr ~: name : same as above, mutatis mutandis
• assert expr : an assertion
• echo expr : debug print

(the current Calder implementation neither does a good job of calculating free variables nor of doing the dataflow scheduling. User beware!)

examples

Factorial (along with 95 equivalents, which mobile fmt will explore):

val
  of fac(7)
!
  fac(n): if
    match n
    !
    m+1 -> n*fac(m)
    !
    0 -> 1
  fi
lav

GCD (along with 767 equivalents, which mobile fmt will explore):

val
  of gcd(6*5*11,6*13*5)
!
  gcd(j,k): if
    match (j-k,k-j)
    !
    (_,m+1) -> gcd(j,k-j)
    !
    0,0 -> j
    !
    (m+1,_) -> gcd(j-k,k)
  fi
lav

mobile

• mobile run prog to run prog.calder

• mobile fmt prog will rewrite prog.calder in an arbitrary order

• mobile dot prog will produce prog.dot suitable for input to Graphviz