One of the styles for writing expressions, with operations '''in''' between the operands, as contrasted to ''postfix'' (operations follow operands, as in [RPN]) and ''prefix'' (operations come before operands, as in [Tcl] in general). Infix notation for mathematical expressions is by far the most common, and is in Tcl supported by [expr].

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As of 2006-10-14, [infix] is also the name of a Tcl package (and command defined by this package) that lets programmers write sequences of mathematical formulae in the familiar infix form. A short example:
  package require infix 0.2
  ::infix::core::setup base base numconst expr::ops expr::fun
  proc ngon_corner {num_sides radius} {
     infix {
        n <- num_sides
        r <- radius
     } {
        alpha = acos(-1) / n ;  # acos(-1) = pi
        r*cos(alpha), r*sin(alpha)
     }
  }
  ngon_corner 6 10 ; # Returns "8.66025403784 5.0" - a two element list

A notable feature is that the [little language] implemented by this package is completely configurable (setting it up for [expr]-like operations is what the ::infix::core::setup command does), so you can define new operations, or define the usual ones to do something unusual. A setting that turns +, -, etc. into the operations of the [math::bignum] package is included with the infix package.

The code is available at
  http://abel.math.umu.se/~lars/tcl/infix.tar.gz
(requires tcllib, tcllib 1.8 is sufficient).

A paper on the package (which includes the entire source code, commented and explained) is available at
  http://abel.math.umu.se/~lars/tcl/infix.pdf

-- [Lars H]

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'''Some kind of a user's manual'''

The user commands created by the package are
    :   '''::infix::core::setup''' ''?module ...?''
Creates a command '''infix''' in the namespace it is called from, 
and loads the listed ''module''s of settings for the little language 
of that '''infix''' command. See below for lists of defined modules and 
the syntax of the '''infix''' command.

    :   '''::infix::core::opalias'''  ''name type cmd ?arg ...?''
Define a new operation ''name'' of type 
''type'' that gets implemented by appending the operand(s) to 
the command prefix ''cmd ?arg ...?'', as specified. Any previous 
meaning of the token ''name'' gets overwritten.

The possible ''type''s include:
   binary ''priority'':   A binary, left-associative operation with priority as specified.
   binary ''priority associativity'':   A binary operation with priority and associativity as specified. Possibilities for ''associativity'' include '''right-associative''', '''non-associative''', and '''n-ary'''.
   prefix ''priority'':   A unary prefix operation with priority as specified.
   postfix ''priority'':   A unary postfix operation with priority as specified.
The priorities should be Tcl numbers (non-integers are fine). Higher priority means tighter binding to the operands. In case of equal priority, the associativity setting is used to resolve which operation acts on which operands. The standard modules uses priorities in the range -2 (for ;) to 14 (for factorial), with + at 10, * at 11, and ** (right-associative) at 12.

    :   '''::infix::core::funalias''' ''name numargs cmd ?arg ...?''
Define a new function ''name'' with 
''numargs'' arguments that gets implemented by appending the 
argument(s) to the command prefix ''cmd ?arg ...?'', as specified. 
Any previous meaning of the token ''name'' gets overwritten. 
''numargs'' may be '''any''' (in which case any number of arguments 
are accepted) or an integer.


'''The infix command'''

The '''infix''' command has the syntax
    :   '''infix''' ''symlinks body''
The ''body'' is where the actual expressions in the infix little language 
are written; the infix command returns the value of (the last statement in) 
the body. The ''symlinks'' argument links symbolic names appearing in 
the ''body'' to Tcl variables in the context from which ''infix'' was called.

To Be Continued...

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[[
[Category Package] |
[Category Mathematics]
]]