Created
June 5, 2019 09:36
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masala parser calculation sample
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| import { C, F, N, Streams } from '@masala/parser' | |
| /* | |
| Implementing general solution : | |
| E -> T E' | |
| E' -> + TE' | eps | |
| T -> F T' | |
| T' -> * FT' | eps | |
| F -> DAY | ( E ) | |
| E== expr | |
| T == subExpr | |
| E'== optPlusExpr | |
| T' == optMultExpr | |
| F == terminal | |
| expr -> subExpr optPlusExpr' | |
| optPlusExpr -> ( + then subExpr then F.lazy(optPlusExpr) ).opt() | |
| subExpr -> terminal then optMultExpr | |
| optMultExpr -> ( * then terminal then F.lazy(optMultExpr) ).opt() | |
| F -> F.try( '(' then expr then ')' ).or(N.litteral) | |
| */ | |
| const MULT = Symbol('MULT') | |
| const PLUS = Symbol('PLUS') | |
| function text() { | |
| return F.not(anyOperation().or(C.charIn('()'))) | |
| .rep() | |
| .map(v => parseInt(v.join('').trim(), 10)) | |
| } | |
| function blank() { | |
| return C.char(' ') | |
| .rep() | |
| .returns(' ') | |
| } | |
| function anyOperation() { | |
| return C.string('*') | |
| .returns(MULT) | |
| .or(C.string('+').returns(PLUS)) | |
| } | |
| function andOperation() { | |
| return C.string('*').returns(MULT) | |
| } | |
| function plusOperation() { | |
| return C.string('+').returns(PLUS) | |
| } | |
| function parenthesis(par) { | |
| return C.char(' ') | |
| .optrep() | |
| .drop() | |
| .then(C.char(par)) | |
| } | |
| function parenthesisExpr() { | |
| return parenthesis('(') | |
| .then(blank().opt()) | |
| .drop() | |
| .then(F.lazy(expr)) | |
| .then( | |
| parenthesis(')') | |
| .then(blank().opt()) | |
| .drop() | |
| ) | |
| } | |
| function expr() { | |
| return subExpr() | |
| .then(optionalPlusExpr()) | |
| .map(v => { | |
| const left = v.at(0) as any | |
| const right = v.at(1) as any | |
| return left + right.orElse(0) | |
| }) | |
| } | |
| function optionalPlusExpr() { | |
| return plusExpr().opt() | |
| } | |
| function plusExpr() { | |
| return plusOperation() | |
| .drop() | |
| .then(subExpr()) | |
| .then(F.lazy(optionalPlusExpr)) | |
| .map(v => { | |
| const left = v.at(0) as any | |
| const right = v.at(1) as any | |
| return left + right.orElse(0) | |
| }) | |
| } | |
| function subExpr() { | |
| return terminal() | |
| .then(optionalMultExpr()) | |
| .map(v => { | |
| const left = v.at(0) as any | |
| const right = v.at(1) as any | |
| return left * right.orElse(1) | |
| }) | |
| } | |
| function optionalMultExpr() { | |
| return multExpr().opt() | |
| } | |
| function multExpr() { | |
| return andOperation() | |
| .drop() | |
| .then(terminal()) | |
| .then(F.lazy(optionalMultExpr)) | |
| .map(v => { | |
| const left = v.at(0) as any | |
| const right = v.at(1) as any | |
| return left * right.orElse(1) | |
| }) | |
| } | |
| function terminal() { | |
| return F.try(parenthesisExpr()).or(text()) | |
| } | |
| function combinator() { | |
| return expr().then(F.eos().drop()) | |
| } | |
| const input = '2 + 3 * ( ( 4 + 10) + ( 4) ) + 1 * -3' | |
| const stream = Streams.ofString(input) | |
| const parsing = combinator().parse(stream) | |
| console.log(input + '=' + JSON.stringify(parsing.value, null, 2)) |
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