! Copyright (C) 2009 Philipp Brüschweiler
! See http://factorcode.org/license.txt for BSD license.
USING: help.syntax help.markup math math.functions prettyprint locals sequences ;
IN: infix

HELP: \infix[[
{ $syntax "infix[[ ... ]]" }
{ $description "Parses the infix code inside the brackets, converts it to stack code and executes it." }
{ $examples
    { $example
        "USING: infix prettyprint ;"
        "IN: scratchpad"
        "infix[[ 8+2*3 ]] ."
        "14"
    } $nl
    { $link postpone: \infix[[ } " isn't that useful by itself, as it can only access literal numbers and no variables. It is designed to be used together with locals; for example with " { $link postpone: \:: } " :"
    { $example
        "USING: infix locals math.functions prettyprint ;"
        "IN: scratchpad"
        ":: quadratic-equation ( a b c -- z- z+ )"
        "    infix[[ (-b-sqrt(b*b-4*a*c)) / (2*a) ]]"
        "    infix[[ (-b+sqrt(b*b-4*a*c)) / (2*a) ]] ;"
        "1 0 -1 quadratic-equation . ."
        "1.0\n-1.0"
    }
} ;

ARTICLE: "infix" "Infix notation"
"The " { $vocab-link "infix" } " vocabulary implements support for infix notation in Factor source code."
{ $subsections
    postpone: \infix[[
    postpone: \INFIX::
}
"The usual infix math operators are supported:"
{ $list
    { $link + }
    { $link - }
    { $link * }
    { $link / }
    { { $snippet "**" } ", which is the infix operator for " { $link ^ } "." }
    { { $snippet "%" } ", which is the infix operator for " { $link mod } "." }
}
"The standard precedence rules apply: Grouping with parentheses before " { $snippet "*" } ", " { $snippet "/" } "and " { $snippet "%" } " before " { $snippet "+" } " and " { $snippet "-" } "."
{ $example
    "USE: infix"
    "infix[[ 5-40/10*2 ]] ."
    "-3"
}
$nl
"You can call Factor words in infix expressions just as you would in C. There are some restrictions on which words are legal to use though:"
{ $list
    "The word must return exactly one value."
    "The word name must consist of the letters a-z, A-Z, _ or 0-9, and the first character can't be a number."
}
{ $example
    "USING: infix locals math.functions ;"
    ":: binary_entropy ( p -- h )"
    "    infix[[ -(p*log(p) + (1-p)*log(1-p)) / log(2) ]] ;"
    "infix[[ binary_entropy( sqrt(0.25) ) ]] ."
    "1.0"
}
$nl
"You can access " { $vocab-link "sequences" } " inside infix expressions with the familiar " { $snippet "seq[index]" } " notation."
{ $example
    "USING: arrays locals infix ;"
    "let[ { 1 2 3 4 } :> myarr infix[[ myarr[4/2]*3 ]] ] ."
    "9"
}
$nl
"You can create sub-" { $vocab-link "sequences" } " inside infix expressions using " { $snippet "seq[from:to]" } " notation."
{ $example
    "USING: arrays locals infix ;"
    "let[ \"foobar\" :> s infix[[ s[0:3] ]] ] ."
    "\"foo\""
}
$nl
"Additionally, you can step through " { $vocab-link "sequences" } " with " { $snippet "seq[from:to:step]" } " notation."
{ $example
    "USING: arrays locals infix ;"
    "let[ \"reverse\" :> s infix[[ s[::-1] ]] ] ."
    "\"esrever\""
}
{ $example
    "USING: arrays locals infix ;"
    "let[ \"0123456789\" :> s infix[[ s[::2] ]] ] ."
    "\"02468\""
}
;

ABOUT: "infix"