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Diffstat (limited to 'ipl/progs/parsex.icn')
| -rw-r--r-- | ipl/progs/parsex.icn | 167 |
1 files changed, 167 insertions, 0 deletions
diff --git a/ipl/progs/parsex.icn b/ipl/progs/parsex.icn new file mode 100644 index 0000000..f5efee9 --- /dev/null +++ b/ipl/progs/parsex.icn @@ -0,0 +1,167 @@ +############################################################################ +# +# File: parsex.icn +# +# Subject: Program to parse arithmetic expressions +# +# Author: Cheyenne Wills +# +# Date: June 10, 1988 +# +############################################################################ +# +# This file is in the public domain. +# +############################################################################ +# +# Adapted from C code written by Allen I. Holub published in the +# Feb 1987 issue of Dr. Dobb's Journal. +# +# General purpose expression analyzer. Can evaluate any expression +# consisting of number and the following operators (listed according +# to precedence level): +# +# () - ! 'str'str' +# * / & +# + - +# < <= > >= == != +# && || +# +# All operators associate left to right unless () are present. +# The top - is a unary minus. +# +# +# <expr> ::= <term> <expr1> +# <expr1> ::= && <term> <expr1> +# ::= || <term> <expr1> +# ::= epsilon +# +# <term> ::= <fact> <term1> +# <term1> ::= < <fact> <term1> +# ::= <= <fact> <term1> +# ::= > <fact> <term1> +# ::= >= <fact> <term1> +# ::= == <fact> <term1> +# ::= != <fact> <term1> +# ::= epsilon +# +# <fact> ::= <part> <fact1> +# <fact1> ::= + <part> <fact1> +# ::= - <part> <fact1> +# ::= - <part> <fact1> +# ::= epsilon +# +# <part> ::= <const> <part1> +# <part1> ::= * <const> <part1> +# ::= / <const> <part1> +# ::= % <const> <part1> +# ::= epsilon +# +# <const> ::= ( <expr> ) +# ::= - ( <expr> ) +# ::= - <const> +# ::= ! <const> +# ::= 's1's2' # compares s1 with s2 0 if ~= else 1 +# ::= NUMBER # number is a lose term any('0123456789.Ee') +# +############################################################################ + +procedure main() + local line + + writes("->") + while line := read() do { + write(parse(line)) + writes("->") + } +end + +procedure parse(exp) + return exp ? expr() +end + +procedure expr(exp) + local lvalue + + lvalue := term() + repeat { + tab(many(' \t')) + if ="&&" then lvalue := iand(term(),lvalue) + else if ="||" then lvalue := ior(term(),lvalue) + else break + } + return lvalue +end + +procedure term() + local lvalue + + lvalue := fact() + repeat { + tab(many(' \t')) + if ="<=" then lvalue := if lvalue <= fact() then 1 else 0 + else if ="<" then lvalue := if lvalue < fact() then 1 else 0 + else if =">=" then lvalue := if lvalue >= fact() then 1 else 0 + else if =">" then lvalue := if lvalue > fact() then 1 else 0 + else if ="==" then lvalue := if lvalue = fact() then 1 else 0 + else if ="!=" then lvalue := if lvalue ~= fact() then 1 else 0 + else break + } + return lvalue +end + +procedure fact() + local lvalue + + lvalue := part() + repeat { + tab(many(' \t')) + if ="+" then lvalue +:= part() + else if ="-" then lvalue -:= part() + else break + } + return lvalue +end + +procedure part() + local lvalue + + lvalue := const() + repeat { + tab(many(' \t')) + if ="*" then lvalue *:= part() + else if ="%" then lvalue %:= part() + else if ="/" then lvalue /:= part() + else break + } + return lvalue +end + +procedure const() + local sign, logical, rval, s1, s2 + + tab(many(' \t')) + + if ="-" then sign := -1 else sign := 1 + if ="!" then logical := 1 else logical := &null + if ="(" then { + rval := expr() + if not match(")") then { + write(&subject) + write(right("",&pos-1,"_"),"^ Mis-matched parenthesis") + } + else move(1) + } + else if ="'" then { + s1 := tab(upto('\'')) + move(1) + s2 := tab(upto('\'')) + move(1) + rval := if s1 === s2 then 1 else 0 + } + else { + rval := tab(many('0123456789.eE')) + } + if \logical then { return if rval = 0 then 1 else 0 } + else return rval * sign +end |