Takmela: Parsing arithmetic expression example (1+2+3)

The next step in learning Takmela's algorithm, after tracing 1+2

expr : expr '+' term 
    | term ;

term : 
    NUM
    ;
    
NUM: [0-9]+;

WS skip: [ \r\n\t]*;

1+2+3

Trace appears confusing? This might help

Call start nonterminal
	#0: Called expr/0 at the top level (will process) Processing expr/0 codePos expr → • expr `+` term inputPos 0 Calling: expr/0 with Cont expr/0 ; expr → expr• `+` term ; expr [already processed] Processing expr/0 codePos expr → • term inputPos 0 Calling: term/0 with Cont expr/0 ; expr → term• ; expr [will process] Processing term/0 codePos term → • NUM inputPos 0 Match NUM to 1, matched; inputPos now 1 Reached end of rule, success! term/0 → 1 New continuations: term/0 → expr/0 ; expr → term• ; expr expr/0 → expr/0 ; expr → expr• `+` term ; expr
term/0 → 1, term('1')
Iteration 0
Worklist - successes jS term/0 → 1 木term('1') Worklist - continuations S⤚ term/0 → expr/0 ; expr → term• nJ expr/0 → expr/0 ; expr → expr• `+` term
	#1: JoinS: term/0 → 1 will resume cont: expr/0 ; expr → term• Processing expr/0 codePos expr → term• inputPos 1 Reached end of rule, success! expr/0 → 1
term/0 → 1, term('1') expr/0 → 1, expr(term('1'))
Iteration 1
Worklist - successes jS expr/0 → 1 木expr(term('1')) Worklist - continuations
	#2: JoinS: expr/0 → 1 will resume cont: expr/0 ; expr → expr• `+` term Processing expr/0 codePos expr → expr• `+` term inputPos 1 Match + to +, matched; inputPos now 2 Calling: term/2 with Cont expr/0 ; expr → expr `+` term• ; expr(expr(term('1')), '+') [will process] Processing term/2 codePos term → • NUM inputPos 2 Match NUM to 2, matched; inputPos now 3 Reached end of rule, success! term/2 → 3 New continuations: term/2 → expr/0 ; expr → expr `+` term• ; expr(expr(term('1')), '+')
term/0 → 1, term('1') expr/0 → 1, expr(term('1')) term/2 → 3, term('2')
	#3: JoinS: expr/0 → 1 will resume cont: Root/0 ; Root → expr• ×Didn't reach end of input, not a successful parse
term/0 → 1, term('1') expr/0 → 1, expr(term('1')) term/2 → 3, term('2')
Iteration 2
Worklist - successes jS term/2 → 3 木term('2') Worklist - continuations S⤚ term/2 → expr/0 ; expr → expr `+` term•
	#4: JoinS: term/2 → 3 will resume cont: expr/0 ; expr → expr `+` term• Processing expr/0 codePos expr → expr `+` term• inputPos 3 Reached end of rule, success! expr/0 → 3
term/0 → 1, term('1') expr/0 → 1, expr(term('1')) term/2 → 3, term('2') expr/0 → 3, expr(expr(term('1')),'+',term('2'))
Iteration 3
Worklist - successes jS expr/0 → 3 木expr(expr(term('1')),'+',term('2')) Worklist - continuations
	#5: JoinS: expr/0 → 3 will resume cont: expr/0 ; expr → expr• `+` term Processing expr/0 codePos expr → expr• `+` term inputPos 3 Match + to +, matched; inputPos now 4 Calling: term/4 with Cont expr/0 ; expr → expr `+` term• ; expr(expr(expr(term('1')), '+', term('2')), '+') [will process] Processing term/4 codePos term → • NUM inputPos 4 Match NUM to 3, matched; inputPos now 5 Reached end of rule, success! term/4 → 5 New continuations: term/4 → expr/0 ; expr → expr `+` term• ; expr(expr(expr(term('1')), '+', term('2')), '+')
term/0 → 1, term('1') expr/0 → 1, expr(term('1')) term/2 → 3, term('2') expr/0 → 3, expr(expr(term('1')),'+',term('2')) term/4 → 5, term('3')
	#6: JoinS: expr/0 → 3 will resume cont: Root/0 ; Root → expr• ×Didn't reach end of input, not a successful parse
term/0 → 1, term('1') expr/0 → 1, expr(term('1')) term/2 → 3, term('2') expr/0 → 3, expr(expr(term('1')),'+',term('2')) term/4 → 5, term('3')
Iteration 4
Worklist - successes jS term/4 → 5 木term('3') Worklist - continuations S⤚ term/4 → expr/0 ; expr → expr `+` term•
	#7: JoinS: term/4 → 5 will resume cont: expr/0 ; expr → expr `+` term• Processing expr/0 codePos expr → expr `+` term• inputPos 5 Reached end of rule, success! expr/0 → 5
term/0 → 1, term('1') expr/0 → 1, expr(term('1')) term/2 → 3, term('2') expr/0 → 3, expr(expr(term('1')),'+',term('2')) term/4 → 5, term('3') expr/0 → 5, expr(expr(expr(term('1')),'+',term('2')),'+',term('3'))
Iteration 5
Worklist - successes jS expr/0 → 5 木expr(expr(expr(term('1')),'+',term('2')),'+',term('3')) Worklist - continuations
	#8: JoinS: expr/0 → 5 will resume cont: expr/0 ; expr → expr• `+` term Processing expr/0 codePos expr → expr• `+` term inputPos 5 Match `+` to (eof), fail
term/0 → 1, term('1') expr/0 → 1, expr(term('1')) term/2 → 3, term('2') expr/0 → 3, expr(expr(term('1')),'+',term('2')) term/4 → 5, term('3') expr/0 → 5, expr(expr(expr(term('1')),'+',term('2')),'+',term('3'))
	#9: JoinS: expr/0 → 5 will resume cont: Root/0 ; Root → expr• ✓Reached end of input, successful parse!
term/0 → 1, term('1') expr/0 → 1, expr(term('1')) term/2 → 3, term('2') expr/0 → 3, expr(expr(term('1')),'+',term('2')) term/4 → 5, term('3') expr/0 → 5, expr(expr(expr(term('1')),'+',term('2')),'+',term('3')) Root/0 → 5, Root(expr(expr(expr(term('1')),'+',term('2')),'+',term('3')))✓
Iteration 6
Worklist - successes nJ Root/0 → 5 木Root(expr(expr(expr(term('1')),'+',term('2')),'+',term('3'))) Worklist - continuations
(No new calls or successes that can be further processed)
Iteration 7 [Fixed point reached]