79 lines
2.7 KiB
Factor
79 lines
2.7 KiB
Factor
! Copyright (C) 2009 Philipp Brüschweiler
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! See http://factorcode.org/license.txt for BSD license.
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USING: help.syntax help.markup math prettyprint locals sequences ;
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IN: infix
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HELP: [infix
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{ $syntax "[infix ... infix]" }
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{ $description "Parses the infix code inside the brackets, converts it to stack code and executes it." }
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{ $examples
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{ $example
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"USING: infix prettyprint ;"
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"IN: scratchpad"
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"[infix 8+2*3 infix] ."
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"14"
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} $nl
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{ $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: :: } " :"
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{ $example
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"USING: infix locals math.functions prettyprint ;"
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"IN: scratchpad"
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":: quadratic-equation ( a b c -- z- z+ )"
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" [infix (-b-sqrt(b*b-4*a*c)) / (2*a) infix]"
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" [infix (-b+sqrt(b*b-4*a*c)) / (2*a) infix] ;"
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"1 0 -1 quadratic-equation . ."
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"1.0\n-1.0"
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}
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} ;
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ARTICLE: "infix" "Infix notation"
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"The " { $vocab-link "infix" } " vocabulary implements support for infix notation in Factor source code."
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{ $subsections
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POSTPONE: [infix
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}
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$nl
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"The usual infix math operators are supported:"
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{ $list
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{ $link + }
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{ $link - }
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{ $link * }
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{ $link / }
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{ { $snippet "%" } ", which is the infix operator for " { $link mod } "." }
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}
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"The standard precedence rules apply: Grouping with parentheses before " { $snippet "*" } ", " { $snippet "/" } "and " { $snippet "%" } " before " { $snippet "+" } " and " { $snippet "-" } "."
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{ $example
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"USE: infix"
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"[infix 5-40/10*2 infix] ."
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"-3"
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}
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$nl
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"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:"
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{ $list
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"The word must return exactly one value."
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"The word name must consist of the letters a-z, A-Z, _ or 0-9, and the first character can't be a number."
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}
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{ $example
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"USING: infix locals math.functions ;"
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":: binary_entropy ( p -- h )"
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" [infix -(p*log(p) + (1-p)*log(1-p)) / log(2) infix] ;"
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"[infix binary_entropy( sqrt(0.25) ) infix] ."
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"1.0"
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}
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$nl
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"You can access " { $vocab-link "sequences" } " inside infix expressions with the familiar " { $snippet "arr[index]" } " notation."
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{ $example
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"USING: arrays locals infix ;"
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"[let { 1 2 3 4 } :> myarr [infix myarr[4/2]*3 infix] ] ."
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"9"
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}
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"Please note: in Factor " { $emphasis "fixnums are sequences too." } " If you are not careful with sequence accesses you may introduce subtle bugs:"
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{ $example
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"USING: arrays infix locals ;"
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":: add-2nd-elements ( x y -- res )"
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" [infix x[1] + y[1] infix] ;"
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"{ 1 2 3 } { 0 1 2 3 } add-2nd-elements ."
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"3"
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}
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;
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ABOUT: "infix"
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